MongoDB Server Parameters for a Self-Managed Deployment

Note

Starting in MongoDB 8.0, LDAP authentication and authorization is deprecated. LDAP is available and will continue to operate without changes throughout the lifetime of MongoDB 8. LDAP will be removed in a future major release.

For details, see LDAP Deprecation.

Synopsis

MongoDB provides a number of configuration options that you can set using:

the setParameter command:
```
db.adminCommand( { setParameter: 1, <parameter>: <value>  } )
```
the setParameter configuration setting:
```
setParameter:
   <parameter1>: <value1>
   ...
```
the --setParameter command-line option for mongod and mongos:
```
mongod --setParameter <parameter>=<value>
mongos --setParameter <parameter>=<value>
```

For additional configuration options, see Self-Managed Configuration File Options, mongod and mongos.

Parameters

Authentication Parameters

allowRolesFromX509Certificates

Available for both mongod and mongos.

Default: true

A boolean flag that allows or disallows the retrieval of authorization roles from client X.509 certificates.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

authenticationMechanisms

Available for both mongod and mongos.

Specifies the list of authentication mechanisms the server accepts. Set this to one or more of the following values. If you specify multiple values, use a comma-separated list and no spaces. For descriptions of the authentication mechanisms, see Authentication on Self-Managed Deployments.

Value	Description
SCRAM-SHA-1	RFC 5802 standard Salted Challenge Response Authentication Mechanism using the SHA-1 hash function.
SCRAM-SHA-256	RFC 7677 standard Salted Challenge Response Authentication Mechanism using the SHA-256 hash function.
MONGODB-X509	MongoDB TLS/SSL certificate authentication.
GSSAPI (Kerberos)	External authentication using Kerberos. This mechanism is available only in MongoDB Enterprise.
PLAIN (LDAP SASL)	External authentication using LDAP. You can also use `PLAIN` for authenticating in-database users. `PLAIN` transmits passwords in plain text. This mechanism is available only in MongoDB Enterprise.
MONGODB-OIDC	OpenID Connect is an authentication layer built on top of OAuth2. This mechanism is available only in MongoDB Enterprise.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to specify both PLAIN and SCRAM-SHA-256 as the authentication mechanisms, use the following command:

mongod --setParameter authenticationMechanisms=PLAIN,SCRAM-SHA-256 --auth

authFailedDelayMs

Available for both mongod and mongos.

Default: 0

Note

Enterprise Feature

Available in MongoDB Enterprise only.

The number of milliseconds to wait before informing clients that their authentication attempt has failed. This parameter may be in the range 0 to 5000, inclusive.

Setting this parameter makes brute-force login attacks on a database more time-consuming. However, clients waiting for a response from the MongoDB server still consume server resources, and this may adversely impact benign login attempts if the server is denying access to many other clients simultaneously.

awsSTSRetryCount

Changed in version 7.0: (Also starting in 6.0.7 and 5.0.18)

In previous versions, AWS IAM authentication retried only when the server returned an HTTP 500 error.

Available for both mongod and mongos.

Type: integer

Default: 2

For MongoDB deployments using AWS IAM credentials or AWS IAM environment variables.

Maximum number of AWS IAM authentication retries after a connection failure.

The following example sets awsSTSRetryCount to 15 retries:

mongod --setParameter awsSTSRetryCount=15

Alternatively, the following examples uses the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, awsSTSRetryCount: 15 } )

clusterAuthMode

Available for both mongod and mongos.

Set the clusterAuthMode to either sendX509 or x509. Useful during rolling upgrade to use x509 for membership authentication to minimize downtime.

For more information about TLS/SSL and MongoDB, see Configure mongod and mongos for TLS/SSL on Self-Managed Deployments and TLS/SSL Configuration for Clients .

This parameter is only available at runtime. To set the parameter, use the setParameter command.

db.adminCommand( { setParameter: 1, clusterAuthMode: "sendX509" } )

enableLocalhostAuthBypass

Available for both mongod and mongos.

Default: true

Specify 0 or false to disable localhost authentication bypass. Enabled by default.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

See Localhost Exception in Self-Managed Deployments for more information.

enforceUserClusterSeparation

Available for both mongod and mongos.

Set to false to disable the O/OU/DC check when clusterAuthMode is keyFile in your configuration file. This allows clients possessing member certificates to authenticate as users stored in the $external database. The server won't start if clusterAuthMode isn't keyFile in your configuration file.

To set the enforceUserClusterSeparation parameter to false, run the following command during startup:

mongod --setParameter enforceUserClusterSeparation=false

JWKSMinimumQuiescePeriodSecs

Available for both mongod and mongos.

Default: 60 seconds (1 minute)

Specifies the minimum time period that must pass between subsequent fetches of a given IdP's JWKSetURI endpoint. If an RSA public key is changed multiple times within the quiesce period, that key may not work as expected for up to a minute unless the quiesce period is manually reduced. If this parameter is set to zero, there is no quiesce period and the key can be refreshed repeatedly.

This parameter is available at both startup and runtime. To set the parameter, use the setParameter setting.

KeysRotationIntervalSec

Available for both mongod and mongos.

Default: 7776000 seconds (90 days)

Specifies the number of seconds for which an HMAC signing key is valid before rotating to the next one. This parameter is intended primarily to facilitate authentication testing.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

ldapConnectionPoolHostRefreshIntervalMillis

Available for mongod only.

Default: 60000

The number of milliseconds in-between health checks of the pooled LDAP connections.

You can only set ldapConnectionPoolHostRefreshIntervalMillis during start-up, and cannot change this setting with the setParameter database command.

ldapConnectionPoolIdleHostTimeoutSecs

Available for mongod only.

Default: 300

The maximum number of seconds that the pooled connections to an LDAP server can remain idle before being closed.

You can only set ldapConnectionPoolIdleHostTimeoutSecs during start-up, and cannot change this setting with the setParameter database command.

ldapConnectionPoolMaximumConnectionsInProgressPerHost

Available for mongod only.

Changed starting in MongoDB versions 5.0.9 and 6.0.0 Changed default value to 2. In previous versions, the default is unset.

Default: 2

The maximum number of in-progress connect operations to each LDAP server.

You can only set ldapConnectionPoolMaximumConnectionsInProgressPerHost during start-up, and cannot change this setting with the setParameter database command.

ldapConnectionPoolMaximumConnectionsPerHost

Available for mongod only.

Changed starting in MongoDB versions 5.0.9 and 6.0.0 Changed default value to 2147483647. In previous versions, the default is unset.

Default: 2147483647

The maximum number of connections to keep open to each LDAP server.

You can only set ldapConnectionPoolMaximumConnectionsPerHost during start-up, and cannot change this setting during run time with the setParameter database command.

ldapConnectionPoolMinimumConnectionsPerHost

Available for mongod only.

Default: 1

The minimum number of connections to keep open to each LDAP server.

You can only set ldapConnectionPoolMinimumConnectionsPerHost during start-up, and cannot change this setting during run time with the setParameter database command.

ldapConnectionPoolUseLatencyForHostPriority

Available for mongod only.

Default: true

A boolean that determines whether the LDAP connection pool (see ldapUseConnectionPool) should use latency of the LDAP servers to determine the connection order (from lowest latency to highest).

You can only set ldapConnectionPoolUseLatencyForHostPriority during start-up, and cannot change this setting during run time with the setParameter database command.

ldapForceMultiThreadMode

Available for both mongod and mongos.

Default: false

Enables the performance of concurrent LDAP operations.

Note

Only if you are certain that your instance of libldap is safe to use in this mode, enable this flag. You may experience crashes of the MongoDB process if the libldap version you are using is not thread safe.

You must use ldapForceMultiThreadMode to use LDAP connection pool. To enable LDAP connection pool, set ldapForceMultiThreadMode and ldapUseConnectionPool to true.

Tip

If you have any concerns regarding your MongoDB version, OS version or libldap version, please contact MongoDB Support.

ldapQueryPassword

Available for mongod only.

Type: string

The password used to bind to an LDAP server. You must use ldapQueryUser with this parameter.

If not set, mongod or mongos does not attempt to bind to the LDAP server.

ldapQueryUser

Available for mongod only.

Type: string

The user that binds to an LDAP server. You must use ldapQueryPassword with this parameter.

If not set, mongod or mongos does not attempt to bind to the LDAP server.

ldapRetryCount

New in version 6.1.

Available for mongod only.

Type: integer

Default: 0

For MongoDB deployments using LDAP Authorization on Self-Managed Deployments.

Number of operation retries by the server LDAP manager after a network error.

For example, the following sets ldapRetryCount to 3 seconds:

mongod --ldapRetryCount=3

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, ldapRetryCount: 3 } )

ldapShouldRefreshUserCacheEntries

New in version 5.2.

Available for mongod only.

Type: boolean

Default: true

For MongoDB deployments using LDAP Authorization on Self-Managed Deployments.

Starting in MongoDB 5.2, the update interval for cached user information retrieved from an LDAP server depends on ldapShouldRefreshUserCacheEntries:

If true, use ldapUserCacheRefreshInterval.
If false, use ldapUserCacheInvalidationInterval.

You can only set ldapShouldRefreshUserCacheEntries during startup in the configuration file or with the --setParameter option on the command line. For example, the following disables ldapShouldRefreshUserCacheEntries:

mongod --setParameter ldapShouldRefreshUserCacheEntries=false

ldapUseConnectionPool

Available for both mongod and mongos.

Specifies whether MongoDB should use connection pooling when connecting to the LDAP server for authentication/authorization.

MongoDB uses the following default values:

true on Windows.
true on Linux where MongoDB Enterprise binaries are linked against libldap_r.
false on Linux where MongoDB Enterprise binaries are linked against libldap.

You can only set ldapUseConnectionPool during start-up, and cannot change this setting with the setParameter database command.

ldapUserCacheInvalidationInterval

Changed in version 5.2.

Available for mongod only.

Default: 30 seconds

Note

Starting in MongoDB 5.2, the update interval for cached user information retrieved from an LDAP server depends on ldapShouldRefreshUserCacheEntries:

If true, use ldapUserCacheRefreshInterval.
If false, use ldapUserCacheInvalidationInterval.

For use with MongoDB deployments using LDAP Authorization on Self-Managed Deployments.

The interval (in seconds) that the mongod instance waits between external user cache flushes. After MongoDB flushes the external user cache, MongoDB reacquires authorization data from the LDAP server the next time an LDAP-authorized user issues an operation.

Increasing the value specified increases the amount of time MongoDB and the LDAP server can be out of sync, but reduces the load on the LDAP server. Conversely, decreasing the value specified decreases the time MongoDB and the LDAP server can be out of sync while increasing the load on the LDAP server.

ldapUserCacheRefreshInterval

New in version 5.2.

Available for mongod only.

Type: integer

Default: 30 seconds

Note

Starting in MongoDB 5.2, the update interval for cached user information retrieved from an LDAP server depends on ldapShouldRefreshUserCacheEntries:

If true, use ldapUserCacheRefreshInterval.
If false, use ldapUserCacheInvalidationInterval.

For MongoDB deployments using LDAP Authorization on Self-Managed Deployments.

The interval in seconds that mongod waits before refreshing the cached user information from the LDAP server.

The maximum interval is 86,400 seconds (24 hours).

For example, the following sets ldapUserCacheRefreshInterval to 4000 seconds:

mongod --setParameter ldapUserCacheRefreshInterval=4000

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, ldapUserCacheRefreshInterval: 4000 } )

ldapUserCacheStalenessInterval

New in version 5.2.

Available for mongod only.

Type: integer

Default: 90 seconds

For MongoDB deployments using LDAP Authorization on Self-Managed Deployments.

The interval in seconds that mongod retains the cached LDAP user information after the last cache refresh.

If more than ldapUserCacheStalenessInterval seconds elapse without a successful refresh of the user information from the LDAP server, then mongod:

Invalidates the cached LDAP user information.
Is unable to authenticate new sessions for LDAP users until mongod connects to the LDAP server and authorizes the LDAP user.
Authorizes any existing sessions that use previously authenticated LDAP users if mongod is unable to connect to the LDAP server. When mongod reconnects to the LDAP server, mongod ensures the LDAP users are correctly authorized.

The maximum interval is 86,400 seconds (24 hours).

For example, the following sets ldapUserCacheStalenessInterval to 4000 seconds:

mongod --setParameter ldapUserCacheStalenessInterval=4000

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, ldapUserCacheStalenessInterval: 4000 } )

maxValidateMemoryUsageMB

Available for mongod only.

New in version 5.0.

Default: 200

The maximum memory usage limit in megabytes for the validate command. If the limit is exceeded, validate returns as many results as possible and warns that not all corruption might be reported because of the limit.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

ocspEnabled

Available for both mongod and mongos.

Available on Linux and macOS.

Default: true

The flag that enables or disables OCSP.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following disables OCSP:

mongod --setParameter ocspEnabled=false ...

Starting in MongoDB 6.0, if ocspEnabled is set to true during initial sync, all nodes must be able to reach the OCSP responder.

If a member fails in the STARTUP2 state, set tlsOCSPVerifyTimeoutSecs to a value that is less than 5.

ocspStaplingRefreshPeriodSecs

Available for both mongod and mongos.

Available on Linux.

The number of seconds to wait before refreshing the stapled OCSP status response. Specify a number greater than or equal to 1.

You can only set ocspStaplingRefreshPeriodSecs during startup in the configuration file or with the --setParameter option on the command line. For example, the following sets the parameter to 3600 seconds:

mongod --setParameter ocspStaplingRefreshPeriodSecs=3600 ...

Starting in MongoDB 5.0, the rotateCertificates command and db.rotateCertificates() method will also refresh any stapled OCSP responses.

Tip

ocspEnabled
tlsOCSPStaplingTimeoutSecs
tlsOCSPVerifyTimeoutSecs

oidcIdentityProviders

Available for mongod only.

Changed in version 8.0: (Also available in 7.3 and 7.0)

Use this parameter to specify identity provider (IDP) configurations when using OpenID Connect Authentication.

oidcIdentityProviders accepts an array of zero or more identity provider (IDP) configurations. An empty array (default) indicates no OpenID Connect support is enabled.

When more than one IDP is defined, oidcIdentityProviders uses the matchPattern field to select an IDP. Array order determines the priority and the first IDP is always selected.

Starting in MongoDB 8.0, when multiple identity providers (IDP) are defined, the oidcIdentityProviders parameter accepts duplicate issuer values as long as the audience value is unique for each issuer. This is also available in versions 7.3 and 7.0.

oidcIdentityProviders Fields

Field

Necessity

Type

Description

issuer

Required

string

The issuer URI of the IdP that the server should accept tokens from. This must match the iss field in any JWT used for authentication.

If you specify an unreachable issuer URI, MongoDB:

Logs a warning.
Continues server startup, which allows you to update the issuer URI.
Reattempts issuer contact. If MongoDB reaches the issuer URI and validates the access token, authentication succeeds. If the issuer URI remains unreachable, authentication fails.

Changed in version 8.0: (Also available in 7.3 and 7.0)

authNamePrefix

Required

string

Unique prefix applied to each generated UserName and RoleName used in authorization. authNamePrefix can only contain the following characters:

alphanumeric characters (combination of a to z and 0 to 9)
hyphens (-)
underscores (_)

matchPattern

Conditional

string

Regex pattern used to determine which IdP should be used. matchPattern matches against usernames. Array order determines the priority and the first IdP is always selected.

matchPattern is required in some configurations, depending on how the user sets supportsHumanFlows:

When only one IdP has supportsHumanFlows set to true (the default), matchPatterns is optional.
When multiple IdP's have supportsHumanFlows set to true (the default), each of these requires matchPatterns.
matchPatterns is optional for any IdP where supportsHumanFlows is set to false.

This is not a security mechanism. matchPattern serves only as an advisory to clients. MongoDB accepts tokens issued by the IdP whose principal names do not match this pattern.

clientId

Conditional

string

ID provided by the IdP to identify the client that receives the access tokens.

Required when supportsHumanFlows is set to true (the default).

audience

Required

string

Specifies the application or service that the access token is intended for.

Starting in MongoDB 7.0, only one audience oidcIdentityProviders field can be specified for OIDC access tokens. audience fields with empty arrays or arrays of multiple strings are invalid.

When more than one IdP is defined, this must be a unique value for each configuration that shares an issuer.

requestScopes

Optional

array[ string ]

Permissions and access levels that MongoDB requests from the IdP.

IMPORTANT: By default, clients such as Compass and mongosh request the oidc and offline_access scopes from the IdP. If the IdP supports neither oidc nor offline_access, the client doesn't request them. If the IdP supports oidc but not offline_access, you must re-authenticate frequently.

principalName

Optional

string

The claim to be extracted from the access token containing MongoDB user identifiers.

The default value is sub (stands for subject).

useAuthorizationClaim

Optional

boolean

Determines if the authorizationClaim is required. The default value is true.

If the useAuthorizationClaim field is set to true, the server requires an authorizationClaim for the identity provider's config. This is the default behavior.

If the useAuthorizationClaim field is set to false, the authorizationClaim field is optional (and ignored if provided). Instead, the server does the following:

Searches the token for a claim whose name is listed in the principalNameClaim field. This is typically named sub. For example:
sub: "spencer.jackson@example.com"
Constructs the internal username by concatenating the authNamePrefix, a forward slash (/), and the contents of the claim identified by principalNameClaim within the access token. For example, with a authNamePrefix field value of "mdbinc", the internal username is:
mdbinc/spencer.jackson@example.com
Looks for the user with this username and authorizes the client with the roles:
```
{ user: "mdbinc/spencer.jackson@example.com",
  db: "$external" }
```

New in version 7.2: (Also available in 7.0.5)

authorizationClaim

Conditional

string

Required, unless useAuthorizationClaim is set to false.

Claim extracted from access token that contains MongoDB role names.

logClaims

Optional

array[ string ]

List of access token claims to include in log and audit messages upon authentication completion.

JWKSPollSecs

Optional

integer

Frequency, in seconds, to request an updated JSON Web Key Set (JWKS) from the IdP. A setting of 0 disables polling.

When more than one IdP is defined, this must be the same value for each configuration that shares an issuer.

supportsHumanFlows

Optional

bool

Whether the OIDC provider supports human or machine workflows. This affects the clientId and matchPattern fields.

You may find it useful to set this field to false with machine workload IdP's to allow them to omit the clientId when it's unneeded.

Default: true.

New in version 7.2.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

opensslCipherConfig

Available for both mongod and mongos.

Available on Linux only

With the use of native TLS/SSL libraries, the parameter opensslCipherConfig is supported for Linux/BSD and no longer supported in Windows and macOS.

Specify the cipher string for OpenSSL when using TLS/SSL encryption. For a list of cipher strings, see https://www.openssl.org/docs/man1.1.1/man1/ciphers.html. Multiple cipher strings can be provided as a colon-separated list.

Note

This parameter is only for use with TLS 1.2 or earlier. To specify cipher suites for use with TLS 1.3, use the opensslCipherSuiteConfig parameter.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

The use of TLS options is preferred over SSL options. The TLS options have the same functionality as the SSL options. The following example configures a mongod with a opensslCipherConfig cipher string of 'HIGH:!EXPORT:!aNULL@STRENGTH':

mongod --setParameter opensslCipherConfig='HIGH:!EXPORT:!aNULL@STRENGTH' --tlsMode requireTLS --tlsCertificateKeyFile Certs/server.pem

opensslCipherSuiteConfig

Available for both mongod and mongos.

New in version 5.0.

Available on Linux only

Specify the list of supported cipher suites OpenSSL should permit when using TLS 1.3 encryption.

For a list of cipher suites for use with TLS 1.3, see https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_set_cipher_list.html. Multiple cipher suites can be provided as a colon-separated list.

Note

This parameter is only for use with TLS 1.3. To specify cipher strings for use with TLS 1.2 or earlier, use the opensslCipherConfig parameter.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following configures a mongod with a opensslCipherSuiteConfig cipher suite of 'TLS_AES_256_GCM_SHA384' for use with TLS 1.3:

mongod --setParameter opensslCipherSuiteConfig='TLS_AES_256_GCM_SHA384' --tlsMode requireTLS --tlsCertificateKeyFile Certs/server.pem

opensslDiffieHellmanParameters

Available for both mongod and mongos.

Available on Linux only

Specify the path to the PEM file that contains the OpenSSL Diffie-Hellman parameters when using TLS 1.2 or previous. Specifying the OpenSSL Diffie-Hellman parameters enables support for Ephemeral Diffie-Hellman (DHE) cipher suites during TLS/SSL encryption.

This parameter is not supported for use with TLS 1.3.

Ephemeral Diffie-Hellman (DHE) cipher suites (and Ephemeral Elliptic Curve Diffie-Hellman (ECDHE) cipher suites) provide Forward Secrecy. Forward Secrecy cipher suites create an ephemeral session key that is protected by the server's private key but never transmitted. This ensures that even if a server's private key is compromised, you cannot decrypt past sessions with the compromised key.

Note

If opensslDiffieHellmanParameters is unset but ECDHE is enabled, MongoDB enables DHE using the ffdhe3072 Diffie-Hellman parameter, as defined in RFC-7919#appendix-A.2. The ffdhe3072 is a strong parameter (specifically, size is greater than 1024). Strong parameters are not supported with Java 6 and 7 unless extended support has been purchased from Oracle.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

If for performance reasons, you need to disable support for DHE cipher suites, use the opensslCipherConfig parameter:

mongod --setParameter opensslCipherConfig='HIGH:!EXPORT:!aNULL:!DHE:!kDHE@STRENGTH' ...

pessimisticConnectivityCheckForAcceptedConnections

Available on Linux only

Type: boolean

Default: false

When set to true, instructs the server to check the connectivity of accepted connections before processing them and to immediately discard connections that the client terminates.

Consider enabling this parameter on smaller instance types. You can use it when you want to trade a small amount of latency on new connection establishment for reduced server work when processing new connections that have already been closed on the client side.

saslauthdPath

Available for both mongod and mongos.

Note

Available only in MongoDB Enterprise (except MongoDB Enterprise for Windows).

Specify the path to the Unix Domain Socket of the saslauthd instance to use for proxy authentication.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

saslHostName

Available for both mongod and mongos.

saslHostName overrides MongoDB's default hostname detection for the purpose of configuring SASL and Kerberos authentication.

saslHostName does not affect the hostname of the mongod or mongos instance for any purpose beyond the configuration of SASL and Kerberos.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Note

saslHostName supports Kerberos authentication and is only included in MongoDB Enterprise. For more information, see the following:

saslServiceName

Available for both mongod and mongos.

Allows users to override the default Kerberos service name component of the Kerberos principal name, on a per-instance basis. If unspecified, the default value is mongodb.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

saslServiceName is only available in MongoDB Enterprise.

Important

Ensure that your driver supports alternate service names.

scramIterationCount

Available for both mongod and mongos.

Default: 10000

Changes the number of hashing iterations used for all new SCRAM-SHA-1 passwords. More iterations increase the amount of time required for clients to authenticate to MongoDB, but makes passwords less susceptible to brute-force attempts. The default value is ideal for most common use cases and requirements.

If you modify this value, it does not change the iteration count for existing passwords. The scramIterationCount value must be 5000 or greater.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the scramIterationCount to 12000.

mongod --setParameter scramIterationCount=12000

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, scramIterationCount: 12000 } )

Tip

scramSHA256IterationCount

Available for both mongod and mongos.

Default: 15000

Changes the number of hashing iterations used for all new SCRAM-SHA-256 passwords. More iterations increase the amount of time required for clients to authenticate to MongoDB, but makes passwords less susceptible to brute-force attempts. The default value is ideal for most common use cases and requirements.

If you modify this value, it does not change iteration count for existing passwords. The scramSHA256IterationCount value must be 5000 or greater.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the scramSHA256IterationCount to 20000.

mongod --setParameter scramSHA256IterationCount=20000

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, scramSHA256IterationCount: 20000 } )

Tip

sslMode

Available for both mongod and mongos.

Set the net.ssl.mode to either preferSSL or requireSSL. Useful during rolling upgrade to TLS/SSL to minimize downtime.

For more information about TLS/SSL and MongoDB, see Configure mongod and mongos for TLS/SSL on Self-Managed Deployments and TLS/SSL Configuration for Clients .

This parameter is only available at runtime. To set the parameter, use the setParameter command.

db.adminCommand( { setParameter: 1, sslMode: "preferSSL" } )

Tip

tlsMode

tlsClusterAuthX509Override

Available for both mongod and mongos.

New in version 7.0.

Overrides the clusterAuthX509 configuration options.

setParameter:
   tlsClusterAuthX509Override: "{ attributes: 'O=MongoDB, OU=MongoDB Server' }"

The parameter supports attributes and extensionValue overrides.

When the server authenticates connections from members, it analyzes the X.509 certificate to determine whether it belongs to a cluster member. If the server uses the attributes setting or the attributes field on the tlsClusterAuthX509Override parameter, it checks the Distinguished Name (DN) values of the certificate. If the extensionValue setting or the extensionValue field of the tlsClusterAuthX509Override parameter is set, it checks the extension values of the certificate. If it finds a match, it authorizes the connection as a peer.

Use this parameter to rotate certificates when the new certificates have different attributes or extension values.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

tlsMode

Available for both mongod and mongos.

Set to either:

preferTLS
requireTLS

The tlsMode parameter is useful during rolling upgrade to TLS/SSL to minimize downtime.

This parameter is only available at runtime. To set the parameter, use the setParameter command.

db.adminCommand( { setParameter: 1, tlsMode: "preferTLS" } )

For more information about TLS/SSL and MongoDB, see Configure mongod and mongos for TLS/SSL on Self-Managed Deployments and TLS/SSL Configuration for Clients .

Tip

sslMode

tlsOCSPStaplingTimeoutSecs

Available for both mongod and mongos.

Available for Linux.

The maximum number of seconds the mongod / mongos instance should wait to receive the OCSP status response for its certificates.

Specify an integer greater than or equal to (>=) 1. If unset, tlsOCSPStaplingTimeoutSecs uses the tlsOCSPVerifyTimeoutSecs value.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following sets the tlsOCSPStaplingTimeoutSecs to 20 seconds:

mongod --setParameter tlsOCSPStaplingTimeoutSecs=20 ...

Tip

ocspEnabled
ocspStaplingRefreshPeriodSecs
tlsOCSPVerifyTimeoutSecs

tlsOCSPVerifyTimeoutSecs

Available for both mongod and mongos.

Available for Linux and Windows.

Default: 5

The maximum number of seconds that the mongod / mongos should wait for the OCSP response when verifying server certificates.

Specify an integer greater than or equal to (>=) 1.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following sets the tlsOCSPVerifyTimeoutSecs to 20 seconds:

mongod --setParameter tlsOCSPVerifyTimeoutSecs=20 ...

Tip

ocspEnabled
ocspStaplingRefreshPeriodSecs
tlsOCSPStaplingTimeoutSecs

tlsUseSystemCA

Available for mongod only.

Type: boolean

Default: false

Specifies whether MongoDB loads TLS certificates that are already available to the operating system's certificate authority.

Important

When starting a mongod instance with TLS/SSL enabled, you must specify a value for the --tlsCAFile flag, the net.tls.CAFile configuration option, or the tlsUseSystemCA parameter.

--tlsCAFile, tls.CAFile, and tlsUseSystemCA are all mutually exclusive.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set tlsUseSystemCA to true:

mongod --setParameter tlsUseSystemCA=true

For more information about TLS/SSL and MongoDB, see Configure mongod and mongos for TLS/SSL on Self-Managed Deployments and TLS/SSL Configuration for Clients .

tlsWithholdClientCertificate

Available for both mongod and mongos.

Default: false

A TLS certificate is set for a mongod or mongos either by the --tlsClusterFile option or by the --tlsCertificateKeyFile option when --tlsClusterFile is not set. If the TLS certificate is set, by default, the instance sends the certificate when initiating intra-cluster communications with other mongod or mongos instances in the deployment. Set tlsWithholdClientCertificate to 1 or true to direct the instance to withhold sending its TLS certificate during these communications. Use this option with --tlsAllowConnectionsWithoutCertificates (to allow inbound connections without certificates) on all members of the deployment. tlsWithholdClientCertificate is mutually exclusive with --clusterAuthMode x509.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

tlsX509ClusterAuthDNOverride

Available for both mongod and mongos.

An alternative Distinguished Name (DN) that the instance can also use to identify members of the deployment.

For a MongoDB deployment that uses X.509 certificates for clusterAuthMode, deployment members identify each other using X.509 certificates ( net.tls.clusterFile, if specified, and net.tls.certificateKeyFile) during intra-cluster communications. For members of the same deployment, the DN from their certificates must have the same Organization attributes (O's), the Organizational Unit attributes (OU's), and the Domain Components (DC's).

If tlsX509ClusterAuthDNOverride is set for a member, the member can also use the override value when comparing the DN components (O's, OU's, and DC's) of the presented certificates. That is the member checks the presented certificates against its net.tls.clusterFile/net.tls.certificateKeyFile. If the DN does not match, the member checks the presented certificate against the tlsX509ClusterAuthDNOverride value.

Note

If set, you must set this parameter on all members of the deployment.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

You can use this parameter for a rolling update of certificates to new certificates that contain a new DN value. See Rotate X.509 Certificates without clusterAuthX509 Attributes on Self-Managed Clusters.

For more information about membership certificate requirements, see Member Certificate Requirements for details.

tlsX509ExpirationWarningThresholdDays

Available for both mongod and mongos.

Default : 30

mongod / mongos logs a warning on connection if the presented X.509 certificate expires within 30 days of the mongod/mongos system clock. Use the tlsX509ExpirationWarningThresholdDays parameter to control the certificate expiration warning threshold:

Increase the parameter value to trigger warnings farther ahead of the certificate expiration date.
Decrease the parameter value to trigger warnings closer to the certificate expiration date.
Set the parameter to 0 to disable the warning.

This parameter has a minimum value of 0.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For more information on X.509 certificate validity, see RFC 5280 4.1.2.5.

userCacheInvalidationIntervalSecs

Available for mongos only.

Default: 30

On a mongos instance, specifies the interval (in seconds) at which the mongos instance checks to determine whether the in-memory cache of user objects has stale data, and if so, clears the cache. If there are no changes to user objects, mongos will not clear the cache.

This parameter has a minimum value of 1 second and a maximum value of 86400 seconds (24 hours).

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

General Parameters

allowDiskUseByDefault

Available for mongod only.

Default: True

Starting in MongoDB 6.0, pipeline stages that require more than 100 megabytes of memory to execute write temporary files to disk by default. These temporary files last for the duration of the pipeline execution and can influence storage space on your instance. In earlier versions of MongoDB, you must pass { allowDiskUse: true } to individual find and aggregate commands to enable this behavior.

Individual find and aggregate commands can override the allowDiskUseByDefault parameter by either:

Using { allowDiskUse: true } to allow writing temporary files out to disk when allowDiskUseByDefault is set to false
Using { allowDiskUse: false } to prohibit writing temporary files out to disk when allowDiskUseByDefault is set to true

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

mongod --setParameter allowDiskUseByDefault=false

allowDiskUseByDefault only works on mongod not mongos. mongos never writes temporary files to disk. Use the setParameter command in a mongosh session that is connected to a running mongod to change the value of the parameter while the server is running:

db.adminCommand(
  {
      setParameter: 1,
      allowDiskUseByDefault: false
  }
)

connPoolMaxConnsPerHost

Available for both mongod and mongos.

Default: 200

Sets the maximum size of the legacy connection pools for outgoing connections to other mongod instances in the global connection pool. The size of a pool does not prevent the creation of additional connections, but does prevent a connection pool from retaining connections in excess of the value of connPoolMaxConnsPerHost.

Note

The parameter is separate from the connections in TaskExecutor pools. See ShardingTaskExecutorPoolMaxSize.

Only adjust this setting if your driver does not pool connections and you're using authentication in the context of a sharded cluster.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter connPoolMaxConnsPerHost=250

connPoolMaxInUseConnsPerHost

Available for both mongod and mongos.

Sets the maximum number of in-use connections at any given time for for outgoing connections to other mongod instances in the legacy global connection pool.

By default, the parameter is unset.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter connPoolMaxInUseConnsPerHost=100

Tip

connPoolMaxConnsPerHost

cursorTimeoutMillis

Available for both mongod and mongos.

Default: 600000 (10 minutes)

Sets the expiration threshold in milliseconds for idle cursors before MongoDB removes them; specifically, MongoDB removes cursors that have been idle for the specified cursorTimeoutMillis.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the cursorTimeoutMillis to 300000 milliseconds (5 minutes).

mongod --setParameter cursorTimeoutMillis=300000

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, cursorTimeoutMillis: 300000 } )

Setting cursorTimeoutMillis to less than or equal to 0 results in all cursors being immediately eligible for timeout. Generally, the timeout value should be greater than the average amount of time for a query to return results. Use tools like the cursor.explain() cursor modifier to analyze the average query time and select an appropriate timeout period.

Warning

MongoDB cleans up orphaned cursors after the cursorTimeoutMillis threshold only if they are not tied to sessions.

MongoDB cleans up cursors linked to sessions with the localLogicalSessionTimeoutMinutes lifecycle, regardless of the cursorTimeoutMillis value. To handle long idle periods, use Mongo.startSession() and refresh the session using the refreshSessions command. For details, see Refresh a Cursor with refreshSessions.

fassertOnLockTimeoutForStepUpDown

New in version 5.3.

Available for both mongod and mongos.

Default: 15 seconds

Allows a server that receives a request to step up or step down, to terminate if it is unable to comply (for example due to faulty server disks) within the timeout. This enables a cluster to successfully elect a new primary node and thus continue to be available.

fassertOnLockTimeoutForStepUpDown defaults to 15 seconds. To disable nodes from fasserting, set fassertOnLockTimeoutForStepUpDown=0.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example disables nodes from fasserting:

mongod --setParameter fassertOnLockTimeoutForStepUpDown=0

globalConnPoolIdleTimeoutMinutes

Available for both mongod and mongos.

Sets the time limit that connection in the legacy global connection pool can remain idle before being closed.

By default, the parameter is unset.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongos --setParameter globalConnPoolIdleTimeoutMinutes=10

httpVerboseLogging

Available for both mongod and mongos.

Adds more verbose tracing for curl on Linux and macOS. Has no affect on Windows.

By default, the parameter is unset.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

mongos --setParameter httpVerboseLogging=true

indexBuildMinAvailableDiskSpaceMB

New in version 7.1.

Available for mongod only.

Default: 500 MB

Sets the minimum available disk space in megabytes required for index builds.

Must be greater than or equal to 0 MB, and less than or equal to 8 TB. 0 disables the minimum disk space requirement.

A new index build cannot be started and a current index build is cancelled if the available disk space is below indexBuildMinAvailableDiskSpaceMB.

Warning

If you increase indexBuildMinAvailableDiskSpaceMB, ensure your server has enough available disk space. Also, if you set indexBuildMinAvailableDiskSpaceMB too high, you might needlessly prevent index builds when there is enough available disk space and indexBuildMinAvailableDiskSpaceMB could be set lower.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets indexBuildMinAvailableDiskSpaceMB to 650 MB:

db.adminCommand( { setParameter: 1, indexBuildMinAvailableDiskSpaceMB: 650 } )

You can also set indexBuildMinAvailableDiskSpaceMB at startup. For example:

mongod --setParameter indexBuildMinAvailableDiskSpaceMB=650

indexMaxNumGeneratedKeysPerDocument

Available for both mongod and mongos.

New in version 5.3.

Default: 100000

Limits the maximum number of keys generated for a document to prevent out of memory errors. It is possible to raise the limit, but if an operation requires more keys than the indexMaxNumGeneratedKeysPerDocument parameter specifies, the operation will fail.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

ingressAdmissionControllerTicketPoolSize

Available for mongod only.

Default: 1000000

Controls the maximum number of operations admitted concurrently to the ingress queue. The default value of 1000000 represents the numerical equivalent of unbounded, which admits all incoming operations up to the default maximum connections that MongoDB allows.

Increasing this value while there are operations waiting on the queue unblocks as many operations as the new pool size permits. Decreasing this value does not block any currently executing operations, but incoming controllable operations are blocked until there are tickets available.

mongod --setParameter ingressAdmissionControllerTicketPoolSize=100000

Warning

Avoid modifying ingressAdmissionControllerTicketPoolSize unless directed by MongoDB engineers. This setting has major implications across both WiredTiger and MongoDB.

ingressConnectionEstablishmentRateLimiterEnabled

New in version 8.2: (also available in 8.1.1 and 8.0.12)

Available for both mongod and mongos.

Type: boolean

Default: false

Determines whether rate limiting for new connection establishment is enabled. When enabled, MongoDB applies rate limiting to control the number of new connections that can be established per second.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

ingressConnectionEstablishmentRatePerSec

New in version 8.2: (also available in 8.1.1 and 8.0.12)

Available for both mongod and mongos.

Type: int32

Default: disabled

Minimum: 1

Specifies the maximum number of new connections that can be established per second when rate limiting is enabled.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

ingressConnectionEstablishmentBurstCapacitySecs

New in version 8.2: (also available in 8.1.1 and 8.0.12)

Available for both mongod and mongos.

Type: double

Default: disabled

Minimum: 1

Describes how many seconds worth of connection establishments that the server can admit before rate limiting begins. This allows the server to handle temporary bursts of connection requests that exceed the rate limit specified by ingressConnectionEstablishmentRatePerSec.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

ingressConnectionEstablishmentMaxQueueDepth

New in version 8.2: (also available in 8.1.1 and 8.0.12)

Available for both mongod and mongos.

Type: int32

Default: 0 (disabled)

Specifies the maximum number of connection attempts in the connection establishment queue. After the queue reaches this number of connection attempts, the server rejects new connection attempts.

The default value of 0 means that the server rejects all connections that will queue for establishment.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

ingressConnectionEstablishmentRateLimiterBypass

New in version 8.2: (also available in 8.1.1 and 8.0.12)

Available for both mongod and mongos.

Type: string array

Default: []

Provides a list of IP addresses and CIDR ranges that the server must exempt from the connection establishment rate limits. This allows specific trusted clients to bypass rate limiting restrictions.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

maxIndexBuildMemoryUsageMegabytes

Available for mongod only.

Default (absolute): 200
Minimum (absolute): 50
Maximum (percent): 0.8

Limits the amount of memory that simultaneous index builds on one collection may consume for their duration. The specified amount of memory is shared between all indexes built using a single createIndexes command or its shell helper db.collection.createIndexes(). Increasing the limit improves sorting performance when the index build process generates and sorts index keys. The memory consumed by an index build is separate from the WiredTiger cache memory (see cacheSizeGB).

Set this value to 0-0.8 to limit builds to a percentage of memory.
Set this value to 1.0 or greater to limit builds to an absolute number of megabytes.

If this setting allocates less than 50 MB, mongod uses a minimum of 50 MB. If the percentage setting is greater than 0.8, mongod uses a maximum of 80% of available memory.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

maxNumActiveUserIndexBuilds

Available for mongod only.

Type: integer

Default: 3

Sets the maximum number of concurrent index builds allowed on the primary. This is a global limit that applies across all collections.

Increasing the value of maxNumActiveUserIndexBuilds allows additional concurrent index builds at the cost of increased pressure on the WiredTiger cache.

System indexes are not limited to maxNumActiveUserIndexBuilds, however a system index build counts against the limit for user index builds.

After the server reaches maxNumActiveUserIndexBuilds, it blocks additional user index builds until the number of concurrent index builds drops below the maxNumActiveUserIndexBuilds limit. If an index build is blocked, the server logs this message:

Too many index builds running simultaneously, waiting until the
number of active index builds is below the threshold.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following command sets a limit of 4 concurrent index builds:

db.adminCommand( { setParameter: 1, maxNumActiveUserIndexBuilds: 4 } )

Note

notablescan does not allow unbounded queries that use a clustered index because the queries require a full collection scan. For more information, see Collection Scans.

reportOpWriteConcernCountersInServerStatus

Available for mongod only.

Default: false

A boolean flag that determines whether the db.serverStatus() method and serverStatus command return opWriteConcernCounters information. [1]

mongod --setParameter reportOpWriteConcernCountersInServerStatus=true

[1]	Enabling `reportOpWriteConcernCountersInServerStatus` can have a negative performance impact; specifically, when running without TLS.

slowConnectionThresholdMillis

New in version 6.3.

Available for both mongod and mongos.

Default: 100

Sets the time limit in milliseconds to log the establishment of slow server connections.

If a connection takes longer to establish than the slowConnectionThresholdMillis parameter, an event is added to the log with the message msg field set to "Slow connection establishment".

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets slowConnectionThresholdMillis to 250 milliseconds.

mongod --setParameter slowConnectionThresholdMillis=250

Or, if using the setParameter command within mongosh:

db.adminCommand( { setParameter: 1, slowConnectionThresholdMillis: 250 } )

Warning

tcmallocAggressiveMemoryDecommit is deprecated in 8.0. MongoDB 8.0 uses an updated version of tcmalloc that improves memory fragmentation and management. See tcmalloc upgrade for more information. To release memory back to the operating system, consider using tcmallocEnableBackgroundThread instead.

tcmallocEnableBackgroundThread

Available for both mongod and mongos.

New in version 8.0.

Type: boolean

Default: true

If set to true, tcmallocEnableBackgroundThread creates a background thread that periodically releases memory back to the operating system. The value of tcmallocReleaseRate determines the rate, in bytes per second, at which the background thread releases memory.

Note

If tcmallocEnableBackgroundThread is true and tcmallocReleaseRate is 0, MongoDB still releases memory.

For improved memory usage, we recommend using the default value of true. To learn more about improvements to performance and memory management, see Upgraded TCMalloc.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

The following operation sets tcmallocEnableBackgroundThread to false:

mongod --setParameter "tcmallocEnableBackgroundThread=false"

tcmallocReleaseRate

Available for both mongod and mongos.

Changed in version 8.0.

Default: 0

Specifies the TCMalloc release rate in bytes per second. Release rate refers to the rate at which MongoDB releases unused memory to the system. If tcmallocReleaseRate is set to 0 MongoDB doesn't release memory back to the system. Increase this value to return memory faster; decrease it to return memory slower.

Note

If tcmallocEnableBackgroundThread is true and tcmallocReleaseRate is 0, MongoDB still releases memory.

Starting in MongoDB 8.0, the default value of tcmallocReleaseRate is reduced to 0 due to a tcmalloc upgrade that prioritizes CPU performance over memory release.

In earlier versions, MongoDB used an older version of tcmalloc that:

Set the default tcmallocReleaseRate to 1.
Accepted values for tcmallocReleaseRate between 0 and 10, inclusive.

Important

If you run MongoDB on a platform that uses tcmalloc-gperf such as Windows, PPC, or s390x, tcmallocReleaseRate has the same behavior as earlier MongoDB versions.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

To modify the release rate during run time, you can use the setParameter command. For example:

db.adminCommand( { setParameter: 1, tcmallocReleaseRate: 2097152 } )

You can also set tcmallocReleaseRate at startup time; for example:

mongod --setParameter "tcmallocReleaseRate=2097152"

tcpFastOpenClient

Available for both mongod and mongos.

Default: true

Linux Operating System Only

Enables support for outbound TCP Fast Open (TFO) connections from the mongod/mongos to a client. TFO requires both the client and the mongod/mongos host machine support and enable TFO.

Linux operating systems running Linux Kernel 4.11 or later can support outbound TFO.

Set the value of /proc/sys/net/ipv4/tcp_fastopen to enable outbound TFO connections:

1 to enable only outbound TFO connections.
3 to enable inbound and outbound TFO connections.

This parameter has no effect if the host operating system does not support or is not configured to support TFO connections.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

RFC7413.

tcpFastOpenQueueSize

Available for both mongod and mongos.

Default: 1024

As part of establishing a TCP Fast Open (TFO) connection, the client submits a valid TFO cookie to the mongod/mongos before completion of the standard TCP 3-way handshake. The mongod/mongos keeps a queue of all such pending TFO connections.

The tcpFastOpenQueueSize parameter sets the size of the queue of pending TFO connections. While the queue is full, the mongod/mongos falls back to the normal three-way handshake for incoming client requests and ignores the presence of TFO cookies. Once the queue size falls back below the limit, the mongod/mongos begins accepting new TFO cookies.

Increasing the default queue size may improve the effect of TFO on network performance. However, large queue sizes also increase the risk of server resource exhaustion due to excessive incoming TFO requests.
Decreasing the default queue size may reduce the risk of resource server resource exhaustion due to excessive incoming TFO requests. However, small queue sizes may also reduce the effect of TFO on network performance.
The minimum queue size is 0. A queue of 0 effectively disables TFO.

This parameter has no effect on host operating systems that do not support or are not configured for TFO connections.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

tcpFastOpenServer

Available for both mongod and mongos.

Default: true

Enables support for accepting inbound TCP Fast Open (TFO) connections to the mongod/mongos from a client. TFO requires both the client and mongod/mongos host machine support and enable TFO:

Windows

The following Windows operating systems support TFO:

Microsoft Windows Server 2016 and later.
Microsoft Windows 10 Update 1607 and later.

macOS

macOS 10.11 (El Capitan) and later support TFO.

Linux

Linux operating systems running Linux Kernel 3.7 or later can support inbound TFO.

Set the value of /proc/sys/net/ipv4/tcp_fastopen to enable inbound TFO connections:

Set to 2 to enable only inbound TFO connections.
Set to 3 to enable inbound and outbound TFO connections.

This parameter has no effect if the host operating system does not support or is not configured to support TFO connections.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

RFC7413.

ttlMonitorEnabled

Available for mongod only.

Default: true

To support TTL Indexes, mongod instances have a background thread that is responsible for deleting documents from collections with TTL indexes.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

To disable this worker thread for a mongod, set ttlMonitorEnabled to false, as in the following operations:

db.adminCommand( { setParameter: 1, ttlMonitorEnabled: false } )

Alternately, you may disable the thread at startup time by starting the mongod instance with the following option:

mongod --setParameter ttlMonitorEnabled=false

Important

Do not run production mongod instances with ttlMonitorEnabled disabled, except under guidance from MongoDB support. Preventing TTL document removal can negatively impact MongoDB internal system operations that depend on TTL Indexes.

watchdogPeriodSeconds

Available for mongod only.

Type: integer

Default: -1 (disabled)

Determines how frequent the Storage Node Watchdog checks the status of the monitored filesystems:

The --dbpath directory
The journal directory inside the --dbpath directory
The directory of --logpath file
The directory of --auditPath file

Valid values for watchdogPeriodSeconds are:

-1 (the default), to disable/pause Storage Node Watchdog, or
An integer greater than or equal to 60.

Note

If a filesystem on a monitored directory becomes unresponsive, it can take a maximum of nearly twice the value of watchdogPeriodSeconds to terminate the mongod.
If any of its monitored directory is a symlink to other volumes, the Storage Node Watchdog does not monitor the symlink target. For example, if the mongod uses storage.directoryPerDB: true (or --directoryperdb) and symlinks a database directory to another volume, the Storage Node Watchdog does not follow the symlink to monitor the target.

To enable Storage Node Watchdog, watchdogPeriodSeconds must be set during startup.

mongod --setParameter watchdogPeriodSeconds=60

You can only enable the Storage Node Watchdog at startup. However, once enabled, you can pause the Storage Node Watchdog or change the watchdogPeriodSeconds during run time.

Once enabled,

To pause the Storage Node Watchdog during run time, set watchdogPeriodSeconds to -1.
```
db.adminCommand( { setParameter: 1, watchdogPeriodSeconds: -1 } )
```
To resume or change the period during run time, set watchdogPeriodSeconds to a number greater than or equal to 60.
```
db.adminCommand( { setParameter: 1, watchdogPeriodSeconds: 120 } )
```

Note

It is an error to set watchdogPeriodSeconds at run time if the Storage Node Watchdog was not enabled at startup time.

Logging Parameters

enableDetailedConnectionHealthMetricLogLines

New in version 7.0.

Available for both mongod and mongos.

Type: boolean

Default: true

Determines whether to enable specific log messages related to cluster connection health metrics. If enableDetailedConnectionHealthMetricLogLines is set to false, the following log messages are turned off, but MongoDB still collects data on the cluster connection health metrics:

Log Message	Description
Accepted TLS connection from peer	Indicates that the server successfully parsed the peer certificate during the TLS handshake with an accepted ingress connection.
Ingress TLS handshake complete	Indicates that the TLS handshake with an ingress connection is complete.
Hello completed	Indicates that the initial connection handshake completed on an incoming client connection. MongoDB displays the log message only with the first `hello` command.
Auth metrics report	Specifies the completion of a step in the authentication conversation.
Received first command on ingress connection since session start or auth handshake	Indicates that an ingress connection received the first command that is not part of the handshake.
Slow network response send time	Indicates that the time spent, in milliseconds, to send the response back to the client over an ingress connection takes more time than the duration defined by the `slowMS` server parameter.
Completed client-side verification of OCSP request	If the peer doesn't include an OCSP response to the TLS handshake when an egress TLS connection is established, the server must send an OCSP request to the certificate authority. MongoDB writes this log message when the certificate authority receives the OCSP response.
Slow connection establishment	Indicates that the time taken to send a response back to the client over an ingress connection takes longer than the threshold specified with the `slowConnectionThresholdMillis` parameter. MongoDB also emits this log message when the connection establishment times out.
Operation timed out while waiting to acquire connection	Indicates that an operation timed out while waiting to acquire an egress connection.
Acquired connection for remote operation and completed writing to wire	Indicates that the server took one millisecond or longer to write an outgoing request on an egress connection, counting from the instant when the connection establishes.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

logComponentVerbosity

Available for both mongod and mongos.

Default: 0

Sets the verbosity levels of various components for log messages. The verbosity level determines the amount of Informational and Debug messages MongoDB outputs. [2]

The verbosity level can range from 0 to 5:

0 is the MongoDB's default log verbosity level, to include Informational messages.
1 to 5 increases the verbosity level to include Debug messages.

For a component, you can also specify -1 to inherit the parent's verbosity level.

To specify the verbosity level, use a document similar to the following:

{
  verbosity: <int>,
  <component1>: { verbosity: <int> },
  <component2>: {
     verbosity: <int>,
     <component3>: { verbosity: <int> }
  },
  ...
}

For the components, you can specify just the <component>: <int> in the document, unless you are setting both the parent verbosity level and that of the child component(s) as well:

{
  verbosity: <int>,
  <component1>: <int> ,
  <component2>: {
     verbosity: <int>,
     <component3>: <int>
  }
  ...
}

The top-level verbosity field corresponds to systemLog.verbosity which sets the default level for all components. The default value of systemLog.verbosity is 0.

The components correspond to the following settings:

Unless explicitly set, the component has the verbosity level of its parent. For example, storage is the parent of storage.journal. That is, if you specify a storage verbosity level, this level also applies to:

storage.journal components unless you specify the verbosity level for storage.journal.
storage.recovery components unless you specify the verbosity level for storage.recovery.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the default verbosity level to 1, the query to 2, the storage to 2, and the storage.journal to 1.

db.adminCommand( {
   setParameter: 1,
   logComponentVerbosity: {
      verbosity: 1,
      query: { verbosity: 2 },
      storage: {
         verbosity: 2,
         journal: {
            verbosity: 1
         }
      }
   }
} )

You can also set parameter logComponentVerbosity at startup time, passing the verbosity level document as a string.

mongod --setParameter "logComponentVerbosity={command: 3}"

mongosh also provides the db.setLogLevel() to set the log level for a single component. For various ways to set the log verbosity level, see Configure Log Verbosity Levels.

[2]	Starting in version 4.2, MongoDB includes the Debug verbosity level (1-5) in the log messages. For example, if the verbosity level is 2, MongoDB logs `D2`. In previous versions, MongoDB log messages only specified `D` for Debug level.

logLevel

Available for both mongod and mongos.

Default: 0 (informational)

Specify an integer between 0 and 5 signifying the verbosity of the logging, where 5 is the most verbose. [3]

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets the logLevel to 2:

db.adminCommand( { setParameter: 1, logLevel: 2 } )

Tip

[3]	Starting in version 4.2, MongoDB includes the Debug verbosity level (1-5) in the log messages. For example, if the verbosity level is 2, MongoDB logs `D2`. In previous versions, MongoDB log messages only specified `D` for Debug level.

maxLogSizeKB

Available for both mongod and mongos.

Type: non-negative integer

Default: 10

Specifies the maximum size, in kilobytes, for an individual attribute field in a log entry; attributes exceeding this limit are truncated.

Truncated attribute fields print field content up to the maxLogSizeKB limit and excise field content past that limit, retaining valid JSON formatting. Log entries that contain truncated attributes append a truncated object to the end of the log entry.

See log message truncation for more information.

A value of 0 disables truncation entirely. Negative values for this parameter are not valid.

Warning

Using a large value, or disabling truncation with a value of 0, may adversely affect system performance and negatively impact database operations.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets the maximum log line size to 20 kilobytes:

mongod --setParameter maxLogSizeKB=20

quiet

Available for both mongod and mongos.

Sets quiet logging mode. If 1, mongod will go into a quiet logging mode which will not log the following events/activities:

connection events;
the drop command, the dropIndexes command, the validate command; and
replication synchronization activities.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Consider the following example which sets the quiet parameter to 1:

db.adminCommand( { setParameter: 1, quiet: 1 } )

Tip

systemLog.quiet

redactClientLogData

Available for both mongod and mongos.

Type: boolean

Note

Enterprise Feature

Available in MongoDB Enterprise only.

Configure the mongod or mongos to redact any message accompanying a given log event before logging. This prevents the program from writing potentially sensitive data stored on the database to the diagnostic log. Metadata such as error or operation codes, line numbers, and source file names are still visible in the logs.

Use redactClientLogData in conjunction with Encryption at Rest and TLS/SSL (Transport Encryption) to assist compliance with regulatory requirements.

To enable log redaction at startup, you can either:

Start mongod with the --redactClientLogData option:
```
mongod --redactClientLogData
```
Set the security.redactClientLogData option in the configuration file:
```
security:
   redactClientLogData: true
   ...
```

You can't use the --setParameter option to set redactClientLogData at startup.

To enable log redaction on a running mongod or mongos, use the following command:

db.adminCommand( { setParameter: 1, redactClientLogData : true } )

Tip

security.redactClientLogData

redactEncryptedFields

New in version 6.1.0.

Available for both mongod and mongos.

Type: boolean

Default: true

Configures mongod and mongos to redact field values of encrypted Binary data from all log messages.

If the redactClientLogData parameter or the security.redactClientLogData setting is set to false and redactEncryptedFields is set to true (the default), encrypted fields are redacted from all log messages.
If the redactClientLogData parameter or security.redactClientLogData setting is set to true, all fields are redacted, regardless of the redactEncryptedFields setting.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

suppressNoTLSPeerCertificateWarning

Available for both mongod and mongos.

Type: boolean

Default: false

By default, a mongod or mongos with TLS/SSL enabled and net.ssl.allowConnectionsWithoutCertificates : true lets clients connect without providing a certificate for validation while logging an warning. Set suppressNoTLSPeerCertificateWarning to 1 or true to suppress those warnings.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

The following operation sets suppressNoTLSPeerCertificateWarning to true:

db.adminCommand( { setParameter: 1, suppressNoTLSPeerCertificateWarning: true} )

traceExceptions

Available for both mongod and mongos.

Configures mongod to log full source code stack traces for every database and socket C++ exception, for use with debugging. If true, mongod will log full stack traces.

This parameter is only available at runtime. To set the parameter, use the setParameter command.

Consider the following example which sets the traceExceptions to true:

db.adminCommand( { setParameter: 1, traceExceptions: true } )

Tip

systemLog.traceAllExceptions

Diagnostic Parameters

To facilitate analysis of the MongoDB server behavior by MongoDB engineers, MongoDB logs server statistics to diagnostic files at periodic intervals.

For mongod, the diagnostic data files are stored in the diagnostic.data directory under the mongod instance's --dbpath or storage.dbPath.

For mongos, the diagnostic data files, by default, are stored in a directory under the mongos instance's --logpath or systemLog.path directory. The diagnostic data directory is computed by truncating the logpath's file extension(s) and concatenating diagnostic.data to the remaining name.

For example, if mongos has --logpath /var/log/mongodb/mongos.log.201708015, then the diagnostic data directory is /var/log/mongodb/mongos.diagnostic.data/ directory. To specify a different diagnostic data directory for mongos, set the diagnosticDataCollectionDirectoryPath parameter.

The following parameters support diagnostic data capture (FTDC):

Note

The default values for the diagnostic data capture interval and the maximum sizes are chosen to provide useful data to MongoDB engineers with minimal impact on performance and storage size. Typically, these values will only need modifications as requested by MongoDB engineers for specific diagnostic purposes.

diagnosticDataCollectionDirectoryPath

Available for mongos only.

Type: String

Warning

If Full Time Diagnostic Data Capture (FTDC) is disabled with diagnosticDataCollectionEnabled or if systemLog.destination is set to syslog, you must restart mongos after setting diagnosticDataCollectionDirectoryPath.

Specify the directory for the diagnostic directory for mongos. If the directory does not exist, mongos creates the directory.

If unspecified, the diagnostic data directory is computed by truncating the mongos instance's --logpath or systemLog.path file extension(s) and concatenating diagnostic.data.

For example, if mongos has --logpath /var/log/mongodb/mongos.log.201708015, then the diagnostic data directory is /var/log/mongodb/mongos.diagnostic.data/.

If the mongos cannot create the specified directory, the diagnostic data capture is disabled for that instance. mongos may not be able to create the specified directory if a file with the same name already exists in the path or if the process does not have permissions to create the directory.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

diagnosticDataCollectionDirectorySizeMB

Available for both mongod and mongos.

Type: integer

Default: 250 (500 in sharded clusters)

Specifies the maximum size, in megabytes, of the diagnostic.data directory. If directory size exceeds this number, the oldest diagnostic files in the directory are automatically deleted based on the timestamp in the file name.

Changed in version 8.0: diagnosticDataCollectionDirectorySizeMB has a default value of 400 MB for mongos and mongod instances used in sharded clusters. mongod instances used in replica set or as standalone servers have a default value of 200 MB.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the maximum size of the directory to 250 megabytes:

mongod --setParameter diagnosticDataCollectionDirectorySizeMB=250

The minimum value for diagnosticDataCollectionDirectorySizeMB is 10 megabytes. diagnosticDataCollectionDirectorySizeMB must be greater than maximum diagnostic file size diagnosticDataCollectionFileSizeMB.

diagnosticDataCollectionEnabled

Available for both mongod and mongos.

Type: boolean

Default: true

Determines whether to enable the collecting and logging of data for diagnostic purposes. Diagnostic logging is enabled by default.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following disables the diagnostic collection:

mongod --setParameter diagnosticDataCollectionEnabled=false

diagnosticDataCollectionFileSizeMB

Available for both mongod and mongos.

Type: integer

Default: 10

Specifies the maximum size, in megabytes, of each diagnostic file. If the file exceeds the maximum file size, MongoDB creates a new file.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the maximum size of each diagnostic file to 20 megabytes:

mongod --setParameter diagnosticDataCollectionFileSizeMB=20

The minimum value for diagnosticDataCollectionFileSizeMB is 1 megabyte.

diagnosticDataCollectionPeriodMillis

Available for both mongod and mongos.

Type: integer

Default: 1000

Specifies the interval, in milliseconds, at which to collect diagnostic data.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, the following sets the interval to 5000 milliseconds or 5 seconds:

mongod --setParameter diagnosticDataCollectionPeriodMillis=5000

The minimum value for diagnosticDataCollectionPeriodMillis is 100 milliseconds.

Replication and Consistency

allowMultipleArbiters

New in version 5.3.

Available for mongod only.

Type: boolean

Default: false

Specifies whether the replica set allows the use of multiple arbiters.

The use of multiple arbiters is not recommended:

Multiple arbiters prevent the reliable use of the majority write concern. MongoDB counts arbiters in calculating a membership majority, but arbiters do not store data. With the inclusion of multiple arbiters, it's possible for a majority write operation to return success before the write replicates to a majority of data bearing nodes.
Multiple arbiters allow replica sets to accept writes even when the replica set doesn't have sufficient secondaries for data replication.

For more information, see Concerns with Multiple Arbiters.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter allowMultipleArbiters=true

connectTimeoutMs

Available for both mongod and mongos.

Type: integer

Default: 10000

Sets the connection timeout, in milliseconds, for the replica set monitor.

This parameter is only available at startup. If you set this parameter, it must be greater than or equal to 500.

The following example sets connectTimeoutMs for a mongod instance to 700 milliseconds:

mongod --setParameter connectTimeoutMs=700

createRollbackDataFiles

Available for mongod only.

Type: boolean

Default: true

Flag that determines whether MongoDB creates rollback files that contains documents affected during a rollback.

By default, createRollbackDataFiles is true and MongoDB creates the rollback files.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets createRollbackDataFiles to false so that the rollback files are not created:

mongod --setParameter createRollbackDataFiles=false

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, createRollbackDataFiles: false } )

For more information, see Collect Rollback Data.

disableSplitHorizonIPCheck

New in version 5.0.0.

Available for both mongod and mongos.

Type: boolean

Default: false

To configure cluster nodes for split horizon DNS, use host names instead of IP addresses.

Starting in MongoDB v5.0, replSetInitiate and replSetReconfig reject configurations that use IP addresses instead of hostnames.

Use disableSplitHorizonIPCheck to modify nodes that cannot be updated to use host names. The parameter only applies to the configuration commands.

mongod and mongos do not rely on disableSplitHorizonIPCheck for validation at startup. Legacy mongod and mongos instances that use IP addresses instead of host names can start after an upgrade.

Instances that are configured with IP addresses log a warning to use host names instead of IP addresses.

To allow configuration changes using IP addresses, set disableSplitHorizonIPCheck=true using the command line:

/usr/local/bin/mongod  --setParameter disableSplitHorizonIPCheck=true -f /etc/mongod.conf

This parameter is only available at startup. To set the parameter, use the setParameter setting.

setParameter:
   disableSplitHorizonIPCheck: true

enableFlowControl

Available for both mongod and mongos.

Type: boolean

Default: true

Enables or disables the mechanism that controls the rate at which the primary applies its writes with the goal of keeping the secondary members' majority committed lag under a configurable maximum value.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

enableOverrideClusterChainingSetting

New in version 5.0.2.

Available for both mongod and mongos.

Type: boolean

Default: false

If enableOverrideClusterChainingSetting is true, replica set secondary members can replicate data from other secondary members even if settings.chainingAllowed is false.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the enableOverrideClusterChainingSetting for a mongod instance to true:

mongod --setParameter enableOverrideClusterChainingSetting=true

flowControlTargetLagSeconds

Available for both mongod and mongos.

Type: integer

Default: 10

The target maximum majority committed lag when running with flow control. When flow control is enabled, the mechanism attempts to keep the majority committed lag under the specified seconds. The parameter has no effect if flow control is disabled.

The specified value must be greater than 0.

In general, the default settings should suffice; however, if modifying from the default value, decreasing, rather than increasing, the value may prove to be more useful.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

flowControlWarnThresholdSeconds

Available for both mongod and mongos.

Type: integer

Default: 10

The amount of time to wait to log a warning once the flow control mechanism detects the majority commit point has not moved.

The specified value must be greater than or equal to 0, with 0 to disable warnings.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

heartBeatFrequencyMs

Available for both mongod and mongos.

Type: integer

Default: 10000

When replicaSetMonitorProtocol is set to 'sdam', heartBeatFrequencyMs determines how long, in milliseconds, to wait between hello requests.

When replicaSetMonitorProtocol is set to 'streamable', heartBeatFrequencyMs determines how long, in milliseconds, to wait between hello round trip time (RTT) measurements. RTT measurements are used in server selection.

This parameter is only available at startup. If you set this parameter, it must be greater than or equal to 500.

The following example sets heartBeatFrequencyMs in a mongod instance to 700 milliseconds:

mongod --setParameter heartBeatFrequencyMs=700

initialSyncIndexBuildMemoryPercentage

New in version 8.2.

Available for mongod only.

Type: double

Default: 10.0

The percentage of system memory that MongoDB allocates for index builds during initial sync. The amount of system memory used is bound by the values of initialSyncIndexBuildMemoryMinMB and initialSyncIndexBuildMemoryMaxMB.

You can specify a value between 0.0 and 80.0, inclusive.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the initialSyncIndexBuildMemoryPercentage for a mongod instance to 40%:

mongod --setParameter initialSyncIndexBuildMemoryPercentage=40

initialSyncIndexBuildMemoryMaxMB

New in version 8.2.

Available for mongod only.

Type: integer

Default: 16384

The maximum amount of system memory, in megabytes, that MongoDB can use for index builds during initial sync.

You can specify a value between 50 and 10000000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the initialSyncIndexBuildMemoryMaxMB for a mongod instance to 20000 MB:

mongod --setParameter initialSyncIndexBuildMemoryMaxMB=20000

initialSyncIndexBuildMemoryMinMB

New in version 8.2.

Available for mongod only.

Type: Integer

Default: 200

The minimum amount of system memory, in megabytes, that MongoDB can use for index builds during initial sync.

You can specify a value between 50 and 10000000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the initialSyncIndexBuildMemoryMinMB for a mongod instance to 60 MB:

mongod --setParameter initialSyncIndexBuildMemoryMinMB=60

initialSyncMethod

New in version 5.2.

Available for mongod only.

Type: String

Default: logical

Available only in MongoDB Enterprise.

Method used for initial sync.

Set to logical to use logical initial sync. Set to fileCopyBased to use file copy based initial sync.

This parameter only affects the sync method for the member on which it is specified. Setting this parameter on a single replica set member does not affect the sync method of any other replica set members.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

initialSyncSourceReadPreference

Available for mongod only.

Type: String

The preferred source for performing initial sync. Specify one of the following read preference modes:

primary
primaryPreferred (Default for voting replica set members)
secondary
secondaryPreferred
nearest (Default for newly added or non-voting replica set members)

If the replica set has disabled chaining, the default initialSyncSourceReadPreference read preference mode is primary.

You cannot specify a tag set or maxStalenessSeconds to initialSyncSourceReadPreference.

If the mongod cannot find a sync source based on the specified read preference, it logs an error and restarts the initial sync process. The mongod exits with an error if it cannot complete the initial sync process after 10 attempts. For more information on sync source selection, see Initial Sync Source Selection.

initialSyncSourceReadPreference takes precedence over the replica set's settings.chainingAllowed setting when selecting an initial sync source. After a replica set member successfully completes initial sync, it defers to the value of chainingAllowed when selecting a replication sync source.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

initialSyncTransientErrorRetryPeriodSeconds

Available for both mongod and mongos.

Type: integer

Default: 86400

The amount of time in seconds a secondary performing initial sync attempts to resume the process if interrupted by a transient network error. The default value is equivalent to 24 hours.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

localLogicalSessionTimeoutMinutes

Available for both mongod and mongos.

Type: integer

Default: 30

Warning

For testing purposes only

This parameter is intended for testing purposes only and not for production use.

The time in minutes that a session remains active after its most recent use. Sessions that have not received a new read/write operation from the client or been refreshed with refreshSessions within this threshold are cleared from the cache. State associated with an expired session may be cleaned up by the server at any time.

This parameter applies only to the instance on which it is set. To set this parameter on replica sets and sharded clusters, you must specify the same value on every member; otherwise, sessions will not function properly.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the localLogicalSessionTimeoutMinutes for a test mongod instance to 20 minutes:

mongod --setParameter localLogicalSessionTimeoutMinutes=20

localThresholdMs

Available for both mongod and mongos.

Type: integer

Default: 15

Defines the length of the latency window used in server selection in milliseconds.

This parameter is only available at startup. If you set this parameter, it must be greater than or equal to 0.

The following example sets localThresholdMs for a mongod instance to 20 milliseconds:

mongod --setParameter localThresholdMs=20

logicalSessionRefreshMillis

Available for both mongod and mongos.

Type: integer

Default: 300000 (5 minutes)

The interval (in milliseconds) at which the cache refreshes its logical session records against the main session store.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the logicalSessionRefreshMillis for a mongod instance to 10 minutes:

mongod --setParameter logicalSessionRefreshMillis=600000

maxAcceptableLogicalClockDriftSecs

Available for both mongod and mongos.

Type: integer

Default: 31536000 (1 year)

The maximum amount by which the current cluster time can be advanced; specifically, maxAcceptableLogicalClockDriftSecs is the maximum difference between the new value of the cluster time and the current cluster time. Cluster time is a logical time used for ordering of operations.

You cannot advance the cluster time to a new value if the new cluster time differs from the current cluster time by more than maxAcceptableLogicalClockDriftSecs.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the maxAcceptableLogicalClockDriftSecs for a mongod instance to 15 minutes:

mongod --setParameter maxAcceptableLogicalClockDriftSecs=900

maxNumSyncSourceChangesPerHour

Available for both mongod and mongos.

New in version 5.0.

Type: integer

Default: 3

Sync sources are evaluated each time a sync source is updated and each time a node fetches a batch of oplog entries. If there are more than maxNumSyncSourceChangesPerHour source changes in an hour, the node temporarily stops re-evaluating that sync source. If this parameter is set with a high value, the node may make unnecessary source changes.

This parameter will not prevent a node from starting to sync from another node if it doesn't have a sync source. The node will re-evaluate if a sync source becomes invalid. Similarly, if the primary changes and chaining is disabled, the node will update to sync from the new primary.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

maxSessions

Available for both mongod and mongos.

Type: integer

Default: 1000000

The maximum number of sessions that can be cached.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the maxSessions for a mongod instance to 1000:

mongod --setParameter maxSessions=1000

mirrorReads

Available for mongod only.

Type: Document

Default: { samplingRate: 0.01, maxTimeMS: 1000 }

Specifies the settings for mirrored reads for the mongod instance. The settings only take effect when the member is a primary.

The parameter mirrorReads takes a JSON document with the following fields:

Field

Description

samplingRate

The sampling rate used to mirror a subset of operations that support mirroring to a subset of electable (specifically, priority greater than 0) secondaries. That is, the primary mirrors reads to each electable secondary at the specified sampling rate.

Valid values are:

`0.0`	Turns off mirroring.
`1.0`	The primary mirrors all operations that supports mirroring to each electable secondary.
Number between `0.0` and `1.0` (exclusive)	The primary randomly samples each electable secondary at the specified rate to be sent mirrored reads.

For example, given a replica set with a primary and two electable secondaries and a sampling rate of 0.10, the primary mirrors reads to each electable secondary at the sampling rate of 10 percent such that one read may be mirrored to one secondary and not to the other or to both or to neither. That is, if the primary receives 100 operations that can be mirrored, the sampling rate of 0.10 may result in 8 reads being mirrored to one secondary and 13 reads to the other or 10 to each, etc.

The default value is 0.01.

maxTimeMS

The maximum time in milliseconds for the mirrored reads. The default value is 1000.

The maxTimeMS for the mirrored reads is separate from the maxTimeMS of the original read being mirrored.

targetedMirroring

Contains fields to configure how you target specific nodes for cache warming. For more information on targeted mirroring, see Targeted Mirrored Reads.

Includes the following fields:

`tag`	Defaults to an empty `BSONObj`. The replica set tag that you can use to target nodes for mirroring. You can configure a node for targeted mirroring using the following syntax: `tag: { "<tag1>": "<string1>" }` You can only supply one tag. All nodes within the same replica set that have these tags are targeted.
`samplingRate`	Type: Float Range: `0.0` to `1.0` (inclusive) The rate at which targeted reads are mirrored to the host or hosts. A rate of `0.0` means no reads are mirrored, and a rate of `1.0` means all reads are mirrored. Although `samplingRate` defaults to `0.01`, the `targetedMirroring` feature is off by default, since the `tag` field defaults to empty.
`maxTimeMS`	Type: int The maximum time in milliseconds before the mirrored read times out. The minumum value for `maxTimeMS` is `0`. Defaults to `1000`.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

If you specify from the configuration file or on the command line, enclose the mirrorReads document in quotes.

For example, the following sets the mirror reads sampling rate to 0.10 from the command line:

mongod --setParameter mirrorReads='{ samplingRate: 0.10 }'

Or, to specify in a configuration file:

setParameter:
   mirrorReads: '{samplingRate: 0.10}'

Or if using the setParameter command in a mongosh session that is connected to a running mongod, do not enclose the document in quotes:

db.adminCommand( { setParameter: 1, mirrorReads: { samplingRate: 0.10 } } )

mirrorReadsMaxConnPoolSize

New in version 8.2.

Type: int

Default: 4

Controls the maximum number of connections in the mirroring pool. This parameter affects both general and targeted mirrored reads. mirrorReadsMaxConnPoolSize has a minimum value of 1.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

oplogBatchDelayMillis

New in version 6.0.

Available for both mongod and mongos.

Type: integer

Default: 0

The number of milliseconds to delay applying batches of oplog operations on secondary nodes. By default, oplogBatchDelayMillis is 0, meaning oplog batches are applied with no delay. When there is no delay, MongoDB may apply frequent, small oplog batches to secondaries.

Increasing oplogBatchDelayMillis causes MongoDB to apply oplog batches less frequently on secondaries, with each batch containing larger amounts of data. This reduces IOPS on secondaries, but adds latency for writes with write concern "majority".

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, run the following command to set the oplogBatchDelayMillis for a mongod instance to 20 milliseconds:

mongod --setParameter oplogBatchDelayMillis=20

oplogFetcherUsesExhaust

Available for mongod only.

Type: boolean

Default: true

Enables or disables streaming replication. Set the value to true to enable streaming replication.

Set the value to false to disable streaming replication. If disabled, secondaries fetch batches of oplog entries by issuing a request to their sync from source and waiting for a response. This requires a network roundtrip for each batch of oplog entries.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

oplogInitialFindMaxSeconds

Available for mongod only.

Type: integer

Default: 60

Maximum time in seconds for a member of a replica set to wait for the find command to finish during data synchronization.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

periodicNoopIntervalSecs

Available for mongod only.

Type: integer

Default: 10

The duration in seconds between noop writes on each individual node.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Note

To modify this value for a MongoDB Atlas cluster, you must contact Atlas Support.

The following example sets the periodicNoopIntervalSecs to 1 second at startup:

mongod --setParameter periodicNoopIntervalSecs=1

replBatchLimitBytes

Available for both mongod and mongos.

Default: 104857600 (100MB)

Sets the maximum oplog application batch size in bytes.

Values can range from 16777216 (16MB) to 104857600 (100MB) inclusive.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets replBatchLimitBytes to 64 MB to limit the oplog application batch size:

mongod --setParameter replBatchLimitBytes=67108864

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, replBatchLimitBytes: 64 * 1024 * 1024 } )

replicaSetMonitorProtocol

Available for both mongod and mongos.

Type: string

Default: "streamable"

Determines which replica set monitor protocol to use. You can set this parameter to "streamable", which is compliant with Server Discovery and Monitoring (SDAM) specification and allows for constant hello requests. You can also set this parameter to "sdam", which is compliant with SDAM specification.

This parameter is only available at startup.

The following example sets replicaSetMonitorProtocol to "sdam" on a mongod instance:

mongod --setParameter replicaSetMonitorProtocol='sdam'

replWriterMinThreadCount

New in version 5.0.

Available for mongod only.

Type: integer

Default: 0

Minimum number of threads to use to apply replicated operations in parallel. Values can range from 0 to 256 inclusive. You can only set replWriterMinThreadCount at startup and cannot change this setting with the setParameter command.

Parallel application of replication operations uses up to replWriterThreadCount threads. If replWriterMinThreadCount is configured with a value less than replWriterThreadCount, the thread pool will timeout idle threads until the total count of threads in the thread pool is equal to replWriterMinThreadCount.

replWriterMinThreadCount must be configured with a value that is less than or equal to replWriterThreadCount.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

replWriterThreadCount

Available for mongod only.

Type: integer

Default: 16

Maximum number of threads to use to apply replicated operations in parallel. Values can range from 1 to 256 inclusive. However, the maximum number of threads used is capped at twice the number of available cores.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

replWriterMinThreadCount

rollbackTimeLimitSecs

Available for mongod only.

Type: 64-bit integer

Default: 86400 (1 day)

Maximum age of data that can be rolled back. Negative values for this parameter are not valid.

If the time between the end of the to-be-rolledback instance's oplog and the first operation after the common point (the last point where the source node and the to-be-rolledback node had the same data) exceeds this value, the rollback will fail.

To effectively have an unlimited rollback period, set the value to 2147483647 which is the maximum value allowed and equivalent to roughly 68 years.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

TransactionRecordMinimumLifetimeMinutes

Available for mongod only.

Type: integer

Default: 30

The minimum lifetime a transaction record exists in the transactions collection before the record becomes eligible for cleanup.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the TransactionRecordMinimumLifetimeMinutes for a mongod instance to 20 minutes:

mongod --setParameter TransactionRecordMinimumLifetimeMinutes=20

Tip

localLogicalSessionTimeoutMinutes

waitForSecondaryBeforeNoopWriteMS

Available for mongod only.

Type: integer

Default: 10

The length of time (in milliseconds) that a secondary must wait if the afterClusterTime is greater than the last applied time from the oplog. After the waitForSecondaryBeforeNoopWriteMS passes, if the afterClusterTime is still greater than the last applied time, the secondary makes a no-op write to advance the last applied time.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets the waitForSecondaryBeforeNoopWriteMS to 20 milliseconds:

mongod --setParameter waitForSecondaryBeforeNoopWriteMS=20

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, waitForSecondaryBeforeNoopWriteMS: 20 } )

Sharding Parameters

analyzeShardKeyCharacteristicsDefaultSampleSize

New in version 7.0.

Available for mongod only.

Type: integer

Default: 10000000

If sampleRate and sampleSize are not set when you run analyzeShardKey, specifies the number of documents to sample when calculating shard key characteristics metrics. Must be greater than 0.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets analyzeShardKeyCharacteristicsDefaultSampleSize to 10000 at startup:

mongod --setParameter analyzeShardKeyCharacteristicsDefaultSampleSize=10000

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, analyzeShardKeyCharacteristicsDefaultSampleSize: 10000 } )

analyzeShardKeyMonotonicityCorrelationCoefficientThreshold

New in version 7.0.

Available for mongod only.

Type: double

Default: 0.7

Specifies the RecordId correlation coefficient threshold used to determine if a shard key is monotonically changing in insertion order. Must be greater than 0 and less than or equal to 1.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets analyzeShardKeyMonotonicityCorrelationCoefficientThreshold to 1 at startup:

mongod --setParameter analyzeShardKeyMonotonicityCorrelationCoefficientThreshold=1

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, analyzeShardKeyMonotonicityCorrelationCoefficientThreshold: 1 } )

analyzeShardKeyNumMostCommonValues

New in version 7.0.

Available for mongod only.

Type: integer

Default: 5

Specifies the number of most common shard key values to return. If the collection contains fewer unique shard keys than this value, analyzeShardKeyNumMostCommonValues returns that number of most common values. Must be greater than 0 and less than or equal to 1000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets analyzeShardKeyNumMostCommonValues to 3 at startup:

mongod --setParameter analyzeShardKeyNumMostCommonValues=3

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, analyzeShardKeyNumMostCommonValues: 3 } )

analyzeShardKeyNumRanges

New in version 7.0.

Available for mongod only.

Type: integer

Default: 100

Specifies the number of ranges to partition the shard key space into when calculating the hotness of shard key ranges. Must be greater than 0 and less than or equal to 10000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets analyzeShardKeyNumRanges to 50 at startup:

mongod --setParameter analyzeShardKeyNumRanges=50

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, analyzeShardKeyNumRanges: 50 } )

analyzeShardKeyNumSamplesPerRange

New in version 7.0.

Available for mongod only.

Type: Non-negative integer

Default: 10

The number of documents to sample per shard key range. Must be a value greater than zero and less than or equal to 10000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets analyzeShardKeyNumSamplesPerRange to 50 at startup:

mongod --setParameter analyzeShardKeyNumSamplesPerRange=50

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, analyzeShardKeyNumSamplesPerRange: 50 } )

autoMergerIntervalSecs

New in version 7.0.

Available for mongod only.

Type: integer

Default: 3600

When AutoMerger is enabled, specifies the amount of time between automerging rounds, in seconds. The default value is 3600 seconds, or one hour.

autoMergerIntervalSecs can only be set on config servers.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets autoMergerIntervalSecs to 7200 seconds, or two hours, at startup:

mongod --setParameter autoMergerIntervalSecs=7200

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, autoMergerIntervalSecs: 7200 } )

autoMergerThrottlingMS

New in version 7.0.

Available for mongod only.

Type: integer

Default: 15000

When AutoMerger is enabled, specifies the minimum amount time between merges initiated by the AutoMerger on the same collection, in milliseconds.

autoMergerThrottlingMS can only be set on config servers.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets autoMergerThrottlingMS to 60000 milliseconds, or one minute, at startup:

mongod --setParameter autoMergerThrottlingMS=60000

During run time, you can set or modify the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, autoMergerThrottlingMS: 60000 } )

balancerMigrationsThrottlingMs

New in version 7.0: (Also available starting in 6.3.1, 6.0.6, 5.0.18)

Available for mongod only.

Type: integer

Default: 1000

Specifies the minimum amount of time between two consecutive balancing rounds. This allows you to throttle the balancing rate. This parameter only takes effect on config server nodes.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets balancerMigrationsThrottlingMs to 2000 milliseconds at startup:

mongod --setParameter balancerMigrationsThrottlingMs=2000

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, balancerMigrationsThrottlingMs: 2000 } )

catalogCacheCollectionMaxEntries

New in version 8.1: (also available starting in 8.0.10, 7.0.22)

Type: integer

Default: 10000

Available for both mongod and mongos.

Maximum number of entries allowed in the catalog cache for collections.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

catalogCacheDatabaseMaxEntries

New in version 8.1: (also available starting in 8.0.10, 7.0.22)

Type: integer

Default: 10000

Available for both mongod and mongos.

Maximum number of entries allowed in the catalog cache for databases.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

chunkDefragmentationThrottlingMS

New in version 5.3.

Available for both mongod and mongos.

Type: integer

Default: 0

Specifies the minimum time period (in milliseconds) between consecutive split and merge commands run by the balancer when the chunks in a sharded collection are defragmented. chunkDefragmentationThrottlingMS limits the rate of split and merge commands.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets chunkDefragmentationThrottlingMS to 10 milliseconds:

mongod --setParameter chunkDefragmentationThrottlingMS=10

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, chunkDefragmentationThrottlingMS: 10 } )

disableResumableRangeDeleter

Available for mongod only.

Type: boolean

Default: false

If set on a shard's primary, specifies if MongoDB pauses range deletion on the shard. If set to true, MongoDB pauses cleanup of ranges containing orphaned documents. The shard can continue to donate chunks to other shards, but the shard does not remove donated documents until you set this parameter to false. This shard can continue to receive chunks from other shards as long as it does not have a pending range deletion task in the config.rangeDeletions collection that overlaps with the incoming chunk's range.

When disableResumableRangeDeleter is true, chunk migrations fail if orphaned documents exist on the recipient shard's primary in the same range as the incoming chunks.

The parameter has no effect on the mongod if it is not the shard's primary.

Important

If you set disableResumableRangeDeleter parameter to true, ensure that you apply it consistently for all members in the shard's replica set. In the event of a failover, this setting's value on the new primary dictates the behavior of the range deleter.

Starting in MongoDB 8.2, you can set disableResumableRangeDeleter during both startup and run time.

To set disableResumableRangeDeleter at startup, use the following command:

mongod --setParameter disableResumableRangeDeleter=false

To set disableResumableRangeDeleter during run time, use the following command:

db.adminCommand( { setParameter: 1, disableResumableRangeDeleter: false } )

enableFinerGrainedCatalogCacheRefresh

Note

Deprecated in 8.0

Starting in MongoDB 8.0, the parameter is deprecated and doesn't cause any changes or errors.

Available for both mongod and mongos.

Type: boolean

Default: true

This parameter allows the catalog cache to be refreshed only if the shard needs to be refreshed. If disabled, any stale chunk will cause the entire chunk distribution for a collection to be considered stale and force all routers who contact the shard to refresh their shard catalog cache.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter enableFinerGrainedCatalogCacheRefresh=true
mongos --setParameter enableFinerGrainedCatalogCacheRefresh=true

Tip

enableShardedIndexConsistencyCheck

Available for mongod only.

Type: boolean

Default: true

If set on the config server's primary, enables or disables the index consistency check for sharded collections. The parameter has no effect on the mongod if it is not the config server's primary.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets enableShardedIndexConsistencyCheck to false for a config server primary:

mongod --setParameter enableShardedIndexConsistencyCheck=false

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, enableShardedIndexConsistencyCheck: false } )

Tip

shardedIndexConsistencyCheckIntervalMS parameter
shardedIndexConsistency metrics returned by the serverStatus command.

findChunksOnConfigTimeoutMS

New in version 5.0.

Available for both mongod and mongos.

Type: Non-negative integer

Default: 900000

The timeout in milliseconds for find operations on chunks.

If there is a large number of chunks in the cluster and chunk loading fails with the error ExceededTimeLimit, increase the parameter value:

mongod --setParameter findChunksOnConfigTimeoutMS=1000000

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

findShardsOnConfigTimeoutMS

Available for both mongod and mongos.

New in version 8.3.

Type: Non-negative integer

Default: 10000 milliseconds

The timeout in milliseconds for find operations against the config.shards namespace.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets findShardsOnConfigTimeoutMS to 15000 milliseconds during runtime:

db.adminCommand( { setParameter: 1, findShardsOnConfigTimeoutMS: 15000 } )

The following example sets findShardsOnConfigTimeoutMS to 15000 milliseconds at startup:

mongos --setParameter findShardsOnConfigTimeoutMS=15000

loadRoutingTableOnStartup

Available for mongos only.

Type: boolean

Default: true

Configures a mongos instance to preload the routing table for a sharded cluster on startup. With this setting enabled, the mongos caches the cluster-wide routing table for each sharded collection as part of its startup procedure, before it begins accepting client connections.

Without this setting enabled, the mongos only loads a routing table as needed for incoming client connections, and only loads the specific routing table for the namespace of a given request.

A mongos instance with the loadRoutingTableOnStartup parameter enabled may experience longer startup times, but will result in faster servicing of initial client connections once started.

loadRoutingTableOnStartup is enabled by default.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

maxCatchUpPercentageBeforeBlockingWrites

New in version 5.0.

Available for mongod only.

Type: integer

Default: 10

For moveChunk and moveRange operations, specifies the maximum percentage of untrasferred data allowed by the migration protocol (expressed in percentage of the total chunk size) to transition from the catchup phase to the commit phase.

Setting a higher catchup percentage can decrease the amount of time it takes for the migration to complete at the cost of increased latency during concurrent upsert and delete operations.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Starting in MongoDB 7.1 (and 7.0.1), you can set the parameter during runtime.

For example, to set the maximum percentage to 20, you can issue the following during startup:

mongod --setParameter maxCatchUpPercentageBeforeBlockingWrites=20

Starting in MongoDB 7.1 (and 7.0.1), you can set the parameter during runtime with the setParameter command:

db.adminCommand( { setParameter: 1, maxCatchUpPercentageBeforeBlockingWrites: 20} )

Tip

Live Migration Protocol

maxTimeMSForHedgedReads: Important
Starting in MongoDB 8.1, hedged reads are removed and this parameter has no effect.

metadataRefreshInTransactionMaxWaitBehindCritSecMS

Deprecated

Note

Starting in MongoDB 8.1, the old metadataRefreshInTransactionMaxWaitBehindCritSecMS parameter is renamed metadataRefreshInTransactionMaxWaitMS. You can continue to use metadataRefreshInTransactionMaxWaitBehindCritSecMS as the parameter name, but it is deprecated and will be removed in a future MongoDB release.

New in version 5.2: (Also available starting in 5.1.0, 5.0.4)

Changed in version 8.1.

Available for mongod only.

Type: integer

Default: 500

Limits the time a shard waits for a critical section within a transaction.

When a query accesses a shard, a chunk migration or DDL operation may already hold the critical section for the collection. If the query finds the critical section is taken, the shard waits until the critical section has been released. When the shard returns control to mongos, mongos retries the query. However, if a multi-shard transaction interacts with an operation that takes the critical section on multiple shards, the interaction can result in a distributed deadlock.

metadataRefreshInTransactionMaxWaitBehindCritSecMS limits the maximum time a shard waits within a transaction for the critical section to be released.

To reduce the maximum wait time for the critical section within a transaction, lower the value of metadataRefreshInTransactionMaxWaitBehindCritSecMS.

Warning

If metadataRefreshInTransactionMaxWaitBehindCritSecMS is too low, mongos could use all of its retry attempts and return an error.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set metadataRefreshInTransactionMaxWaitBehindCritSecMS to 400 milliseconds:

db.adminCommand( { setParameter: 1, metadataRefreshInTransactionMaxWaitBehindCritSecMS: 400 } )

metadataRefreshInTransactionMaxWaitMS

Changed in version 8.1.

Available for mongod only.

Type: integer

Default: 500

Limits the time a shard waits for a critical section within a transaction.

Note

metadataRefreshInTransactionMaxWaitMS limits the maximum time a shard waits within a transaction for the critical section to be released.

To reduce the maximum wait time for the critical section within a transaction, lower the value of metadataRefreshInTransactionMaxWaitMS.

Warning

If metadataRefreshInTransactionMaxWaitMS is too low, mongos could use all of its retry attempts and return an error.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set metadataRefreshInTransactionMaxWaitMS to 400 milliseconds:

db.adminCommand( { setParameter: 1, metadataRefreshInTransactionMaxWaitMS: 400 } )

migrateCloneInsertionBatchDelayMS

Available for mongod only.

Type: Non-negative integer

Default: 0

Time in milliseconds to wait between batches of insertions during cloning step of the migration process. This wait is in addition to the secondaryThrottle.

The default value of 0 indicates no additional wait.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the migrateCloneInsertionBatchDelayMS to 200 milliseconds:

mongod --setParameter migrateCloneInsertionBatchDelayMS=200

The parameter may also be set using the setParameter command:

db.adminCommand( { setParameter: 1, migrateCloneInsertionBatchDelayMS: 200 } )

migrateCloneInsertionBatchSize

Available for mongod only.

Type: Non-negative integer

Default: 0

The maximum number of documents to insert in a single batch during the cloning step of the migration process.

The default value of 0 indicates no maximum number of documents per batch. However, in practice, this results in batches that contain up to 16 MB of documents.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the migrateCloneInsertionBatchSize to 100 documents:

mongod --setParameter migrateCloneInsertionBatchSize=100

The parameter may also be set using the setParameter command:

db.adminCommand( { setParameter: 1, migrateCloneInsertionBatchSize: 100 } )

mongosShutdownTimeoutMillisForSignaledShutdown

New in version 5.0.

Available for mongos only.

Type: integer

Default: 15000

Specifies the time (in milliseconds) to wait for any ongoing database operations to complete before initiating a shutdown of mongos in response to a SIGTERM signal.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the time to 250 milliseconds, you can issue the following during startup:

mongos --setParameter mongosShutdownTimeoutMillisForSignaledShutdown=250

Or if using the setParameter command in a mongosh session that is connected to a running mongos:

db.adminCommand( { setParameter: 1, mongosShutdownTimeoutMillisForSignaledShutdown: 250 } )

opportunisticSecondaryTargeting: Important
Starting in MongoDB 8.1, hedged reads are removed and this parameter has no effect.

orphanCleanupDelaySecs

Changed in version 8.2.

Available for mongod only.

Default: 3600 (60 minutes)

Minimum delay before a migrated chunk is deleted from the source shard.

Before deleting a migrated chunk, MongoDB waits for in-progress queries involving the chunk to complete on the shard primary and then waits an additional orphanCleanupDelaySecs seconds.

Starting in 8.2, the behavior of in-progress queries on shard secondaries is determined by terminateSecondaryReadsOnOrphanCleanup.

If a shard has storage constraints, consider reducing this value temporarily. If running queries that exceed 60 minutes on shard secondaries, consider increasing this value.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the orphanCleanupDelaySecs to 20 minutes:

mongod --setParameter orphanCleanupDelaySecs=1200

This may also be set using the setParameter command:

db.adminCommand( { setParameter: 1, orphanCleanupDelaySecs: 1200 } )

Tip

In all versions, the new value of orphanCleanupDelaySecs is only applied to range deletions created after the value is changed. To apply the new value to existing range deletions, force a step down.

persistedChunkCacheUpdateMaxBatchSize

New in version 7.2: (and 7.1.1, 7.0.4, 6.0.13, 5.0.25)

Available for mongod only.

Type: Integer

Default: 1000

To route and serve operations, shards must know the routing and ownership information associated with their collections. This information propogates from a shard's primary node to its secondary nodes through the replication of the internal cache collections config.cache.collections and config.cache.chunks.<collectionName>.

In previous versions, updates on the chunk cache collection were performed individually (meaning that an entry was deleted and a new entry was inserted). Starting in MongoDB 7.2, these updates are performed as a batch of deletions followed by a batch of insertions. The updated logic improves performance for collections that contain a large number of chunks.

The persistedChunkCacheUpdateMaxBatchSize parameter specifies the maximum batch size used for updating the persisted chunk cache.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets persistedChunkCacheUpdateMaxBatchSize to 700 at startup:

mongod --setParameter persistedChunkCacheUpdateMaxBatchSize=700

You can also set persistedChunkCacheUpdateMaxBatchSize during runtime:

db.adminCommand( { setParameter: 1, persistedChunkCacheUpdateMaxBatchSize: 700 } )

queryAnalysisSampleExpirationSecs

New in version 7.0.

Available for mongod only.

Type: integer

Default: 7 * 24 * 3600

Amount of time that a sampled query document exists before being removed by the TTL monitor, in seconds. Must be greater than 0.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets queryAnalysisSampleExpirationSecs to 691200 (8 * 24 * 3600) at startup on a mongod instance:

mongod --setParameter queryAnalysisSampleExpirationSecs=691200

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, queryAnalysisSampleExpirationSecs: 691200 } )

queryAnalysisSamplerConfigurationRefreshSecs

New in version 7.0.

Changed in version 7.0.1.

Available for both mongod and mongos.

Type: integer

Default: 10

Interval that a sampler (mongos or mongod) refreshes its query analyzer sample rates.

The sample rate configured by the configureQueryAnalyzer command is divided among mongos instances in the sharded cluster or mongod instances in the replica set based on the traffic going through them. To make the sample rate assignment for a mongos or mongod more responsive to the traffic going through it, decrease this value.

We recommend using the default value.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Starting in MongoDB 7.0.1, you can set queryAnalysisSamplerConfigurationRefreshSecs during run time.

This example sets queryAnalysisSamplerConfigurationRefreshSecs to 60 seconds at startup on a mongod instance:

mongod --setParameter queryAnalysisSamplerConfigurationRefreshSecs=60

This example sets queryAnalysisSamplerConfigurationRefreshSecs to 60 seconds at startup on a mongos instance:

mongos --setParameter queryAnalysisSamplerConfigurationRefreshSecs=60

To set the value to 30 seconds, run the following:

db.adminCommand( { setParameter: 1, queryAnalysisSamplerConfigurationRefreshSecs: 30 } )

queryAnalysisWriterIntervalSecs

New in version 7.0.

Changed in version 7.0.1.

Available for mongod only.

Type: integer

Default: 90

Interval that sampled queries are written to disk, in seconds.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Starting in MongoDB 7.0.1, you can set queryAnalysisWriterIntervalSecs during run time.

This example sets queryAnalysisWriterIntervalSecs to 60 seconds at startup on a mongod instance:

mongod --setParameter queryAnalysisWriterIntervalSecs=60

To set the value to 60 seconds, run the following:

db.adminCommand( { setParameter: 1, queryAnalysisWriterIntervalSecs: 60 } )

queryAnalysisWriterMaxBatchSize

New in version 7.0.

Available for mongod only.

Type: integer

Default: 100000

Maximum number of sampled queries to write to disk at once. Must be greater than 0 and less than or equal to 100000.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets queryAnalysisWriterMaxBatchSize to 1000 at startup on a mongod instance:

mongod --setParameter queryAnalysisWriterMaxBatchSize=1000

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, queryAnalysisWriterMaxBatchSize: 1000 } )

queryAnalysisWriterMaxMemoryUsageBytes

New in version 7.0.

Available for mongod only.

Type: integer

Default: 100 * 1024 * 1024

Maximum amount of memory in bytes that the query sampling writer is allowed to use. Once the limit is reached, all new queries and diffs are discarded from sampling until the buffer is flushed. Must be greater than 0.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

This example sets queryAnalysisWriterMaxMemoryUsageBytes to 10000000 at startup on a mongod instance:

mongod --setParameter queryAnalysisWriterMaxMemoryUsageBytes=10000000

rangeDeleterBatchDelayMS

Available for mongod only.

Type: Non-negative integer

Default: 20

The amount of time in milliseconds to wait before the next batch of deletion during the cleanup stage of range migration.

The _secondaryThrottle replication delay occurs after each batch deletion.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the rangeDeleterBatchDelayMS to 200 milliseconds:

mongod --setParameter rangeDeleterBatchDelayMS=200

The parameter may also be set using the setParameter command:

db.adminCommand( { setParameter: 1, rangeDeleterBatchDelayMS: 200 } )

Tip

In versions prior to 6.0.3, the new value of rangeDeleterBatchDelayMS is only applied to range deletions created after the value is changed. To apply the new value to existing range deletions, force a step down.

From 6.0.3 on, the new value of the parameter is applied to all the range deletions processed after the update, regardless of when the range deletion was created.

rangeDeleterBatchSize

Available for mongod only.

Type: Non-negative integer

Default: 2147483647 starting in MongoDB 5.1.2 and 5.0.6

The maximum number of documents in each batch to delete during the cleanup stage of range migration.

A value of 0 indicates that the system chooses the default value.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets rangeDeleterBatchSize to 32 documents:

mongod --setParameter rangeDeleterBatchSize=32

The parameter may also be set using the setParameter command:

db.adminCommand( { setParameter: 1, rangeDeleterBatchSize: 32 } )

Tip

In versions prior to 6.0.3, the new value of rangeDeleterBatchSize is only applied to range deletions created after the value is changed. To apply the new value to existing range deletions, force a step down.

From 6.0.3 on, the new value of the parameter is applied to all the range deletions processed after the update, regardless of when the range deletion was created.

readHedgingMode: Important
Starting in MongoDB 8.1, hedged reads are removed and this parameter has no effect.

routingTableCacheChunkBucketSize

New in version 7.0.1.

Changed in version 7.2.

Available for both mongod and mongos.

Type: integer

Default: 500

Specifies the size of the routing table cache buckets used to implement chunk grouping optimization. Must be greater than 0.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, to set the cache chunk bucket size to 250 on a mongod, issue the following command at startup:

mongod --setParameter routingTableCacheChunkBucketSize=250

shardedIndexConsistencyCheckIntervalMS

Available for mongod only.

Type: integer

Default: 600000

If set on the config server's primary, the interval, in milliseconds, at which the config server's primary checks the index consistency of sharded collections. The parameter has no effect on the mongod if it is not the config server's primary.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following sets the interval at 300000 milliseconds (5 minutes) at startup:

mongod --setParameter shardedIndexConsistencyCheckIntervalMS=300000

Tip

enableShardedIndexConsistencyCheck parameter
shardedIndexConsistency metrics returned by the serverStatus command.

ShardingTaskExecutorPoolHostTimeoutMS

Available for both mongod and mongos.

Type: integer

Default: 300000 (5 minutes)

Maximum time that mongos goes without communication to a host before mongos drops all connections to the host.

If set, ShardingTaskExecutorPoolHostTimeoutMS should be greater than the sum of ShardingTaskExecutorPoolRefreshRequirementMS and ShardingTaskExecutorPoolRefreshTimeoutMS. Otherwise, mongos adjusts the value of ShardingTaskExecutorPoolHostTimeoutMS to be greater than the sum.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolHostTimeoutMS to 120000 during startup:

mongos --setParameter ShardingTaskExecutorPoolHostTimeoutMS=120000

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolHostTimeoutMS: 120000 } )

ShardingTaskExecutorPoolMaxConnecting

Available for both mongod and mongos.

Type: integer

Default: 2

Maximum number of simultaneous initiating connections (including pending connections in setup/refresh state) each TaskExecutor connection pool can have to a mongod instance. You can set this parameter to control the rate at which mongos adds connections to a mongod instance.

If set, ShardingTaskExecutorPoolMaxConnecting should be less than or equal to ShardingTaskExecutorPoolMaxSize. If it is greater, mongos ignores the ShardingTaskExecutorPoolMaxConnecting value.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolMaxConnecting to 20 during startup:

mongos --setParameter ShardingTaskExecutorPoolMaxConnecting=20

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolMaxConnecting: 20 } )

ShardingTaskExecutorPoolMaxSize

Available for both mongod and mongos.

Type: integer

Default: 2 ⁶⁴ - 1

Maximum number of outbound connections each TaskExecutor connection pool can open to any given mongod instance. The maximum possible connections to any given host across all TaskExecutor pools is:

ShardingTaskExecutorPoolMaxSize * taskExecutorPoolSize

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolMaxSize to 20 during startup:

mongos --setParameter ShardingTaskExecutorPoolMaxSize=20

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolMaxSize: 20 } )

mongos can have up to n TaskExecutor connection pools, where n is the number of cores. See taskExecutorPoolSize.

Tip

ShardingTaskExecutorPoolMinSize

ShardingTaskExecutorPoolMaxSizeForConfigServers

New in version 6.0.

Available for both mongod and mongos.

Type: integer

Default: -1

Optional override for ShardingTaskExecutorPoolMaxSize to set the maximum number of outbound connections each TaskExecutor connection pool can open to a configuration server.

When set to:

-1, ShardingTaskExecutorPoolMaxSize is used. This is the default.
an integer value greater than -1, overrides the maximum number of outbound connections each TaskExecutor connection pool can open to a configuration server.

Parameter only applies to sharded deployments.

The following example sets ShardingTaskExecutorPoolMaxSize to 2 during startup, which sets the maximum number of outbound connections each TaskExecutor connection pool can open to a configuration server to 2:

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

mongos --setParameter ShardingTaskExecutorPoolMaxSizeForConfigServers=2

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolMaxSizeForConfigServers: 2 } )

ShardingTaskExecutorPoolMinSize

Available for both mongod and mongos.

Type: integer

Default: 1

Minimum number of outbound connections each TaskExecutor connection pool can open to any given mongod instance.

ShardingTaskExecutorPoolMinSize connections are created the first time a connection to a new host is requested from the pool. While the pool is idle, the pool maintains this number of connections until ShardingTaskExecutorPoolHostTimeoutMS milliseconds pass without any application using that pool.

For a mongos using the warmMinConnectionsInShardingTaskExecutorPoolOnStartup parameter, the ShardingTaskExecutorPoolMinSize parameter also controls how many connections to each shard host are established on startup of the mongos instance before it begins accepting incoming client connections.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolMinSize to 2 during startup:

mongos --setParameter ShardingTaskExecutorPoolMinSize=2

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolMinSize: 2 } )

mongos can have up to n TaskExecutor connection pools, where n is the number of cores. See taskExecutorPoolSize.

Tip

ShardingTaskExecutorPoolMaxSize
warmMinConnectionsInShardingTaskExecutorPoolOnStartup

ShardingTaskExecutorPoolMinSizeForConfigServers

New in version 6.0.

Available for both mongod and mongos.

Type: integer

Default: -1

Optional override for ShardingTaskExecutorPoolMinSize to set the minimum number of outbound connections each TaskExecutor connection pool can open to a configuration server.

When set to:

-1, ShardingTaskExecutorPoolMinSize is used. This is the default.
an integer value greater than -1, overrides the minimum number of outbound connections each TaskExecutor connection pool can open to a configuration server.

Parameter only applies to sharded deployments.

The following example sets ShardingTaskExecutorPoolMinSize to 2 during startup, which sets the minimum number of outbound connections each TaskExecutor connection pool can open to a configuration server to 2:

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

mongos --setParameter ShardingTaskExecutorPoolMinSizeForConfigServers=2

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolMinSizeForConfigServers: 2 } )

ShardingTaskExecutorPoolRefreshRequirementMS

Available for both mongod and mongos.

Type: integer

Default: 60000 (1 minute)

Maximum time the mongos waits before attempting to heartbeat an idle connection in the pool. An idle connection may be discarded during the refresh if the pool is above its minimum size.

If set, ShardingTaskExecutorPoolRefreshRequirementMS should be greater than ShardingTaskExecutorPoolRefreshTimeoutMS. Otherwise, mongos adjusts the value of ShardingTaskExecutorPoolRefreshTimeoutMS to be less than ShardingTaskExecutorPoolRefreshRequirementMS.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolRefreshRequirementMS to 90000 during startup:

mongos --setParameter ShardingTaskExecutorPoolRefreshRequirementMS=90000

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolRefreshRequirementMS: 90000 } )

ShardingTaskExecutorPoolRefreshTimeoutMS

Available for both mongod and mongos.

Type: integer

Default: 20000 (20 seconds)

Maximum time the mongos waits for a heartbeat before timing out the heartbeat.

If set, ShardingTaskExecutorPoolRefreshTimeoutMS should be less than ShardingTaskExecutorPoolRefreshRequirementMS. Otherwise, mongos adjusts the value of ShardingTaskExecutorPoolRefreshTimeoutMS to be less than ShardingTaskExecutorPoolRefreshRequirementMS.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets ShardingTaskExecutorPoolRefreshTimeoutMS to 30000 during startup:

mongos --setParameter ShardingTaskExecutorPoolRefreshTimeoutMS=30000

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, ShardingTaskExecutorPoolRefreshTimeoutMS: 30000 } )

ShardingTaskExecutorPoolReplicaSetMatching

Changed in version 5.0.

Available for both mongod and mongos.

Type: string

Default: "automatic"

On a mongos instance, this parameter sets the policy that determines the minimum size limit of its connection pools to nodes within replica sets.

On a mongod instance, this parameter sets the policy that determines the minimum size limit of its connection pools to nodes within other replica sets.

Note that this parameter only manages connections for operations that are directly related to user requests and CRUD operations.

Available values are:

Matching Policy	Description
`"automatic"` (Default)	Starting in 5.0, `"automatic"` is the new default value. When set for a `mongos`, the instance follows the behavior specified for the `"matchPrimaryNode"` option. When set for a `mongod`, the instance follows the behavior specified for the `"disabled"` option. WARNING: If the `ShardingTaskExecutorPoolReplicaSetMatching` is set to `"automatic"`, the `replicaSetMatchingStrategy` still describes the actual policy being used, not `"automatic"`. To find the value of the `ShardingTaskExecutorPoolReplicaSetMatching`, use `getParameter` which returns the value of the server parameter.
`"matchPrimaryNode"`	When set for a `mongos`, the minimum size limit of the instance's connection pool to each secondary of a replica set in the sharded cluster (specifically, shard replica set and config servers) is equal to the size of its connection pool to that replica set's primary. When set for a `mongod`, the minimum size limit of the instance's connection pool to each secondary of another replica set in the sharded cluster (specifically, shard replica set and config servers) is equal to the size of its connection pool to that replica set's primary. WARNING: If multiple shard servers in your topology can experience a rapid influx of cross-shard operations, do not set this option on your `mongod` instances. In case of a primary stepdown, `matchPrimaryNode` ensures that any secondary that becomes the primary can handle the current level of primary reads and writes.
`"matchBusiestNode"`	When set for a `mongos`, the instance's minimum size limit of the connection pool to each member of a replica set in the sharded cluster (specifically, shard replica set and config servers) is equal to the largest among the active connection counts to the primary and each secondary member of that replica set. When set for a `mongod`, the instance's minimum size limit of the connection pool to each member of another replica set in the sharded cluster (specifically, shard replica set and config servers) is equal to the largest among the active connection counts to the primary and each secondary member of that replica set. With `"matchBusiestNode"`, `mongos` maintains enough connections to each secondary to handle the current level of primary and secondary reads and writes. The number of connections to maintain in the pool decreases as the number of active connections decreases.
`"disabled"`	When set for a `mongos`, the instance's minimum number of connections in the instance's connection pool to each node of a replica set in the sharded clusterv (specifically, shard replica set and config servers) is equal to the `ShardingTaskExecutorPoolMinSize`. When set for a `mongod`, the instance's minimum number of connections in the instance's connection pool to each node of another replica set in the sharded cluster (specifically, shard replica set and config servers) is equal to the `ShardingTaskExecutorPoolMinSize`.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets the ShardingTaskExecutorPoolReplicaSetMatching to "automatic" during startup:

mongod --setParameter ShardingTaskExecutorPoolReplicaSetMatching="automatic"

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1,  ShardingTaskExecutorPoolReplicaSetMatching: "automatic" } )

shutdownTimeoutMillisForSignaledShutdown

New in version 5.0.

Available for mongod only.

Type: integer

Default: 15000

Specifies the time (in milliseconds) to wait for any ongoing database operations to complete before initiating a shutdown of mongod in response to a SIGTERM signal.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the time to 250 milliseconds, you can issue the following during startup:

mongod --setParameter shutdownTimeoutMillisForSignaledShutdown=250

Or if using the setParameter command in a mongosh session that is connected to a running mongod:

db.adminCommand( { setParameter: 1, shutdownTimeoutMillisForSignaledShutdown: 250 } )

skipShardingConfigurationChecks

Available for mongod only.

Type: boolean

Default: false

When true, allows for starting a shard member or config server member as a standalone for maintenance operations. This parameter is mutually exclusive with the --configsvr or --shardsvr options.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter skipShardingConfigurationChecks=true

Important

Once maintenance has completed, remove the skipShardingConfigurationChecks parameter when restarting the mongod.

taskExecutorPoolSize

Available for mongos only.

Type: integer

Default: 1

The number of Task Executor connection pools to use for a given mongos.

If the parameter value is 0 or less, the number of Task Executor connection pools is the number of cores with the following exceptions:

If the number of cores is less than 4, the number of Task Executor connection pools is 4.
If the number of cores is greater than 64, the number of Task Executor connection pools is 64.

The default value of taskExecutorPoolSize is 1:

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

mongos --setParameter taskExecutorPoolSize=6

Tip

ShardingTaskExecutorPoolMaxSize
ShardingTaskExecutorPoolMinSize

terminateSecondaryReadsOnOrphanCleanup

Available for mongod only.

New in version 8.2.

Type: boolean

Default: true

Controls whether long-running read operations on secondary nodes automatically terminate before orphaned document deletion following a chunk migration.

In sharded clusters, when a chunk successfully migrates from the source shard to the destination shard, MongoDB does not immediately remove the migrated documents from the source shard. Instead, the primary of the source shard waits for any in-progress reads involving the namespace of the migrated chunk to complete, and after that, waits an additional period controlled by orphanCleanupDelaySecs (default: 1 hour). This additional delay allows any long-running secondary reads to finish before orphaned documents are deleted from the source shard.

After the orphaned documents are deleted from the source shard, any ongoing reads running on secondary nodes that started before the chunk migration may silently miss documents without returning an error unless terminateSecondaryReadsOnOrphanCleanup is set to true.

When terminateSecondaryReadsOnOrphanCleanup is set to true, read operations on secondary nodes that began before the chunk migration commit are automatically terminated before the orphaned documents are removed from the secondary node. This prevents long-running secondary reads from silently missing documents that were moved during migration.

When set to false, read operations on secondary nodes continue executing even after orphaned documents are deleted. Operations may silently miss documents without returning an error. This matches the behavior in MongoDB versions before 8.2.

Note

This behavior only affects read operations that start before the chunk migration commit. It applies to all read operations on secondaries, including queries, aggregations, and operations spanning multiple namespaces.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Error Response

When a read operation terminates due to terminateSecondaryReadsOnOrphanCleanup, MongoDB returns the following error:

{
  code: 175, 
  name: QueryPlanKilled, 
  categories: [CursorInvalidatedError], 
  errmsg: "Read has been terminated due to orphan range cleanup"
}

This error is not retryable by design. To learn more about handling these errors, see Long-Running Secondary Reads in Sharded Clusters.

warmMinConnectionsInShardingTaskExecutorPoolOnStartup

Available for mongos only.

Type: boolean

Default: true

Configures a mongos instance to prewarm its connection pool on startup. With this parameter enabled, the mongos attempts to establish ShardingTaskExecutorPoolMinSize network connections to each shard server as part of its startup procedure, before it begins accepting client connections.

A timeout for this behavior can be configured with the warmMinConnectionsInShardingTaskExecutorPoolOnStartupWaitMS parameter. If this timeout is reached, the mongos will begin accepting client connections regardless of the size of its connection pool.

A mongos instance with this parameter enabled may experience longer startup times, but will result in faster servicing of initial client connections once started.

warmMinConnectionsInShardingTaskExecutorPoolOnStartup is enabled by default.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

warmMinConnectionsInShardingTaskExecutorPoolOnStartupWaitMS
ShardingTaskExecutorPoolMinSize

warmMinConnectionsInShardingTaskExecutorPoolOnStartupWaitMS

Available for mongos only.

Type: integer

Default: 2000 (2 seconds)

Sets the timeout threshold in milliseconds for a mongos to wait for ShardingTaskExecutorPoolMinSize connections to be established per shard host when using the warmMinConnectionsInShardingTaskExecutorPoolOnStartup parameter. If this timeout is reached, the mongos will begin accepting client connections regardless of the size of its connection pool.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

Tip

warmMinConnectionsInShardingTaskExecutorPoolOnStartup
ShardingTaskExecutorPoolMinSize

Health Manager Parameters

activeFaultDurationSecs

Available for mongos only.

Type: Document

The amount of time to wait from a Health Managers Overview failure until the mongos is removed from the cluster, in seconds.

When a failure is detected and a Health Manager is configured as critical, the server waits for the specified interval before removing the mongos from the cluster.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For example, to set the duration from failure to crash to five minutes, issue the following at startup:

mongos --setParameter activeFaultDurationSecs=300

Or if using the setParameter command in a mongosh session that is connected to a running mongos:

db.adminCommand(
  {
      setParameter: 1,
      activeFaultDurationSecs: 300
  }
)

Parameters set with setParameter do not persist across restarts. See the setParameter page for details.

To make this setting persistent, set activeFaultDurationSecs in your mongos config file using the setParameter option as in the following example:

setParameter:
   activeFaultDurationSecs: 300

healthMonitoringIntensities

Available for mongos only.

Type: Array of documents

Use this parameter to set intensity levels for Health Managers.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

healthMonitoringIntensities accepts an array of documents, values. Each document in values takes two fields:

type, the Health Manager facet
intensity, the intensity level

Health Managers

Facet	What the Health Observer Checks
`configServer`	Cluster health issues related to connectivity to the config server.
`dns`	Cluster health issues related to DNS availability and functionality.
`ldap`	Cluster health issues related to LDAP availability and functionality.

Intensity Levels

Intensity Level	Description
`critical`	The Health Manager on this facet is enabled and has the ability to move the failing mongos out of the cluster if an error occurs. The Health Manager waits the amount of time specified by `activeFaultDurationSecs` before stopping and moving the mongos out of the cluster automatically.
`non-critical`	The Health Manager on this facet is enabled and logs errors, but the mongos remains in the cluster if errors are encountered.
`off`	The Health Manager on this facet is disabled. The mongos does not perform any health checks on this facet. This is the default intensity level.

For example, to set the dns Health Manager facet to the critical intensity level, issue the following at startup:

mongos --setParameter 'healthMonitoringIntensities={ values:[ { type:"dns", intensity: "critical"} ] }'

Or if using the setParameter command in a mongosh session that is connected to a running mongos:

db.adminCommand(
  {
      setParameter: 1,
      healthMonitoringIntensities: { values: [ { type: "dns", intensity: "critical" } ] } } )
  }
)

Parameters set with setParameter do not persist across restarts. See the setParameter page for details.

To make this setting persistent, set healthMonitoringIntensities in your mongos config file using the setParameter option as in the following example:

setParameter:
   healthMonitoringIntensities: "{ values:[ { type:\"dns\", intensity: \"critical\"} ] }"

healthMonitoringIntervals

Available for mongos only.

Type: Array of documents

How often this Health Manager will run, in milliseconds.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

healthMonitoringIntervals accepts an array of documents, values. Each document in values takes two fields:

type, the Health Manager facet
interval, the time interval it runs at, in milliseconds

Health Managers

Facet	What the Health Observer Checks
`configServer`	Cluster health issues related to connectivity to the config server.
`dns`	Cluster health issues related to DNS availability and functionality.
`ldap`	Cluster health issues related to LDAP availability and functionality.

For example, to set the ldap Health Manager facet to the run health checks every 30 seconds, issue the following at startup:

mongos --setParameter 'healthMonitoringIntervals={ values:[ { type:"ldap", interval: "30000"} ] }'

Or if using the setParameter command in a mongosh session that is connected to a running mongos:

db.adminCommand(
  {
      setParameter: 1,
      healthMonitoringIntervals: { values: [ { type: "ldap", interval: "30000" } ] } } )
  }
)

Parameters set with setParameter do not persist across restarts. See the setParameter page for details.

To make this setting persistent, set healthMonitoringIntervals in your mongos config file using the setParameter option as in the following example:

setParameter:
   healthMonitoringIntervals: "{ values: [{type: \"ldap\", interval: 200}] }"

progressMonitor

Available for mongos only.

Type: Document

Progress Monitor runs tests to ensure that Health Manager checks do not become stuck or unresponsive. Progress Monitor runs these tests in intervals specified by interval. If a health check begins but does not complete within the timeout given by deadline, Progress Monitor stops the mongos and removes it from the cluster.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

`progressMonitor` Fields

Field	Description	Units
`interval`	How often to ensure Health Managers are not stuck or unresponsive.	Milliseconds
`deadline`	Timeout before automatically failing the mongos if a Health Manager check is not making progress.	Seconds

To set the interval to 1000 milliseconds and the deadline to 300 seconds, issue the following at startup:

mongos --setParameter 'progressMonitor={"interval": 1000, "deadline": 300}'

Or if using the setParameter command in a mongosh session that is connected to a running mongos:

db.adminCommand(
  {
      setParameter: 1,
      progressMonitor: { interval: 1000, deadline: 300 } )
  }
)

Parameters set with setParameter do not persist across restarts. See the setParameter page for details.

To make this setting persistent, set progressMonitor in your mongos config file using the setParameter option as in the following example:

setParameter:
   progressMonitor: "{ interval: 1000, deadline: 300 }"

Storage Parameters

enableAutoCompaction

Available for both mongod and mongos.

New in version 8.1.0.

Type: boolean

Default: false

Specifies whether the instance runs automatic background compaction.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

The following example enables automatic background compaction on the instance:

mongod --setParameter "enableAutoCompaction=true"

honorSystemUmask

Available for mongod only.

Default: false

If honorSystemUmask is set to true, new files created by MongoDB have permissions in accordance with the user's umask settings. You cannot set processUmask if honorSystemUmask is set to true.

If honorSystemUmask is set to false, new files created by MongoDB have permissions set to 600, which gives read and write permissions only to the owner. New directories have permissions set to 700. You can use processUmask to override the default permissions for groups and other users on all new files created by MongoDB.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

mongod --setParameter honorSystemUmask=true

Note

honorSystemUmask is not available on Windows systems.

journalCommitInterval

Available for mongod only.

Specify an integer between 1 and 500 signifying the number of milliseconds (ms) between journal commits.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Consider the following example which sets the journalCommitInterval to 200 ms:

db.adminCommand( { setParameter: 1, journalCommitInterval: 200 } )

Tip

storage.journal.commitIntervalMs

minSnapshotHistoryWindowInSeconds

New in version 5.0.

Available for mongod only.

Default: 300

The minimum time window in seconds for which the storage engine keeps the snapshot history. If you query data using read concern "snapshot" and specify an atClusterTime value older than the specified minSnapshotHistoryWindowInSeconds, mongod returns a SnapshotTooOld error.

Warning

In sharded clusters, changing the default minSnapshotHistoryWindowInSeconds value on config server nodes may cause internal operations to fail.

Do not set minSnapshotHistoryWindowInSeconds to 0 on config server nodes. Setting this parameter to 0 causes internal operations conducting snapshot reads targeting the config server with a specified atClusterTime to fail.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Specify an integer greater than or equal to (>=) 0.

Consider the following example which sets the minSnapshotHistoryWindowInSeconds to 600 seconds:

db.adminCommand( { setParameter: 1, minSnapshotHistoryWindowInSeconds: 600 } )

Note

Increasing the value of minSnapshotHistoryWindowInSeconds increases disk usage. For more information, see Snapshot History Retention.

To modify this value for a MongoDB Atlas cluster, you must contact Atlas Support.

processUmask

Available for mongod only.

Overrides the default permissions used for groups and other users when honorSystemUmask is set to false. By default, when honorSystemUmask is set to false, new files created by MongoDB have permissions set to 600. Use the processUmask parameter to override this default with a custom umask value. The file owner inherits permissions from the system umask.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

You cannot set this parameter if honorSystemUmask is set to true.

Consider the following example, which sets the permissions for groups and other users to read/write only and retains the system umask settings for the owner:

mongod --setParameter processUmask=011

Note

processUmask is not available on Windows systems.

storageEngineConcurrentReadTransactions

Changed in version 7.0.

Available for mongod only.

Type: integer

Specifies the maximum number of concurrent read transactions (read tickets) allowed into the storage engine.

Note

Starting in version 7.0, MongoDB dynamically adjusts the number of tickets to optimize performance, with a highest possible value of 128.

Modifying this value can cause performance issues or errors. To determine if disabling the dynamic concurrent storage engine transactions algorithm is optimal for the cluster, contact MongoDB Support.

Starting in MongoDB 7.0, this parameter is available for all storage engines. In earlier versions, this parameter is available for the WiredTiger storage engine only.

Tip

queues.execution

storageEngineConcurrentWriteTransactions

Changed in version 7.0.

Available for mongod only.

Type: integer

Specifies the maximum number of concurrent write transactions allowed into the WiredTiger storage engine.

Note

Starting in version 7.0, MongoDB dynamically adjusts the number of tickets to optimize performance, with a highest possible value of 128.

Starting in MongoDB 7.0, this parameter is available for all storage engines. In earlier versions, this parameter is available for the WiredTiger storage engine only.

Tip

queues.execution

syncdelay

Available for mongod only.

Default: 60

Specify the interval in seconds when mongod flushes its working memory to disk. By default, mongod flushes memory to disk every 60 seconds. In almost every situation you should not set this value and use the default setting.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Consider the following example which sets the syncdelay to 60 seconds:

db.adminCommand( { setParameter: 1, syncdelay: 60 } )

To provide durable data, WiredTiger uses checkpoints. For more details, see Journaling and the WiredTiger Storage Engine.

Tip

temporarilyUnavailableBackoffBaseMs

Available for mongod only.

Default: 1000

Specifies the initial delay before retying a write operation that was rolled back due to cache pressure.

In rare circumstances, a write can fail due to cache pressure. When this happens MongoDB issues a TemporarilyUnavailable error and increments the temporarilyUnavailableErrors counter in two places: the slow query log and the Full Time Diagnostic Data Capture (FTDC).

Individual operations within multi-document transactions never return TemporarilyUnavailable errors.

Adjust the write retry properties by modifying the temporarilyUnavailableBackoffBaseMs and temporarilyUnavailableMaxRetries parameters.

The parameter accepts:

Value	Description
`integer >= 0`	Defaults to 1 second. The initial delay between retries. The value increases with each retry to a maximum of 55 seconds. A larger value increases the chance that the cache pressure will be reduced before the next retry. To configure number of retries, use `temporarilyUnavailableMaxRetries`.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

To set a new value, use db.adminCommand():

db.adminCommand( { setParameter: 1, temporarilyUnavailableBackoffBaseMs: 3 } )

New in version 6.1.0.

temporarilyUnavailableMaxRetries

Available for mongod only.

Default: 10

Specifies the maximum number of retries when a write operation is rolled back due to cache pressure.

Individual operations within multi-document transactions never return TemporarilyUnavailable errors.

Adjust the write retry properties by modifying the temporarilyUnavailableBackoffBaseMs and temporarilyUnavailableMaxRetries parameters.

The parameter accepts:

Value	Description
`integer >= 0`	The maximum number of retries. There is an increasing delay between retries. To configure the backoff time, use `temporarilyUnavailableBackoffBaseMs`.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

To set a new value, use db.adminCommand():

db.adminCommand( { setParameter: 1, temporarilyUnavailableMaxRetries: 5 } )

New in version 6.1.0.

upsertMaxRetryAttemptsOnDuplicateKeyError

Available for both mongod and mongos.

New in version 8.1.0.

Maximum number of retry attempts when an upsert operation encounters a duplicate key error.

Type: Integer

Default: 100

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

Important

Starting in MongoDB 8.1, if an upsert operation runs in a multidocument transaction, then the upsert does not retry when it encounters a duplicate key error.

The following example sets the maximum number of times the server retries an upsert operation when encountering a duplicate key error to 50.

mongod --setParameter "upsertMaxRetryAttemptsOnDuplicateKeyError=50"

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( {
   setParameter: 1,
   upsertMaxRetryAttemptsOnDuplicateKeyError: 50
} )

WiredTiger Parameters

wiredTigerConcurrentReadTransactions

Available for mongod only.

Type: integer

Specifies the maximum number of concurrent read transactions (read tickets) allowed into the storage engine.

Note

Starting in version 7.0, MongoDB dynamically adjusts the number of tickets to optimize performance, with a highest possible value of 128.

Starting in MongoDB 7.0, this parameter is available for all storage engines. In earlier versions, this parameter is available for the WiredTiger storage engine only.

Changed in version 6.0.

The wiredTigerConcurrentReadTransactions parameter was renamed to storageEngineConcurrentReadTransactions.

wiredTigerConcurrentWriteTransactions

Available for mongod only.

Type: integer

Specifies the maximum number of concurrent write transactions allowed into the WiredTiger storage engine.

Note

Starting in version 7.0, MongoDB dynamically adjusts the number of tickets to optimize performance, with a highest possible value of 128.

Starting in MongoDB 7.0, this parameter is available for all storage engines. In earlier versions, this parameter is available for the WiredTiger storage engine only.

Changed in version 6.0.

The wiredTigerConcurrentWriteTransactions parameter was renamed to storageEngineConcurrentWriteTransactions.

wiredTigerEngineRuntimeConfig

Available for mongod only.

Specify wiredTiger storage engine configuration options for a running mongod instance.

This parameter is only available at runtime. To set the parameter, use the setParameter command.

Warning

Avoid modifying the wiredTigerEngineRuntimeConfig unless under the direction from MongoDB engineers as this setting has major implication across both WiredTiger and MongoDB.

Consider the following operation prototype:

db.adminCommand({
   "setParameter": 1,
   "wiredTigerEngineRuntimeConfig": "<option>=<setting>,<option>=<setting>"
})

wiredTigerFileHandleCloseIdleTime

Available for mongod only.

Type: integer

Default: 600

Specifies the amount of time in seconds that a file handle in wiredTiger can remain idle before being closed.

If you set wiredTigerFileHandleCloseIdleTime to 0, idle handles are not closed.

Tip

This parameter is case sensitive. If you capitalize the w in wiredTigerFileHandleCloseIdleTime and run the parameter, the operation returns the following error message:

{ "code":2,"codeName":"BadValue","errmsg":"Unknown --setParameter 'WiredTigerFileHandleCloseIdleTime'" }

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example:

mongod --setParameter wiredTigerFileHandleCloseIdleTime=100000

wiredTigerSessionMax

New in version 8.1.

Type: 32-bit integer

Default: 33000

Available for mongod only.

Maximum number of sessions allowed by WiredTiger.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

See the WiredTiger documentation for all available WiredTiger configuration options.

Auditing Parameters

auditAuthorizationSuccess

Available for both mongod and mongos.

Type: boolean

Default: false

Note

Available only in MongoDB Enterprise and MongoDB Atlas.

Enables the auditing of authorization successes for the authCheck action.

When auditAuthorizationSuccess is false, the audit system only logs the authorization failures for authCheck.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

To enable the audit of authorization successes, issue the following command:

db.adminCommand( { setParameter: 1, auditAuthorizationSuccess: true } )

Enabling auditAuthorizationSuccess degrades performance more than logging only the authorization failures.

If runtime audit configuration is enabled, the auditAuthorizationSuccess parameter should not appear in the mongod or mongos configuration file. The server will fail to start if the parameter is present.

Tip

getParameter

auditConfigPollingFrequencySecs

Available for both mongod and mongos.

New in version 5.0.

Type: integer

Default: 300

A sharded cluster may have servers which maintain audit configuration settings for the cluster. Set the interval, in seconds, for non-configured servers to poll a config server for the current audit generation. If this value returned differs from the previously known value, the initiating node will request the current configuration and update its internal state.

Note

Using the default value of 300 seconds, non-config nodes may lag up to 5 minutes after you set the auditConfig cluster parameter.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

auditEncryptionHeaderMetadataFile

New in version 6.0.

Available for both mongod and mongos.

Type: string

Note

Available only in MongoDB Enterprise. MongoDB Enterprise and Atlas have different configuration requirements.

Path and file name for logging metadata audit headers for audit log encryption. A header is placed at the top of each audit log file and contains metadata for decrypting the audit log. The headers are also stored in the audit log.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

For example, the following sets the path and file for auditEncryptionHeaderMetadataFile:

mongod --setParameter auditEncryptionHeaderMetadataFile=/auditFiles/auditHeadersMetadataFile.log

auditEncryptKeyWithKMIPGet

New in version 6.0.

Available for both mongod and mongos.

Type: boolean

Default: false

Note

Available only in MongoDB Enterprise. MongoDB Enterprise and Atlas have different configuration requirements.

Enables audit log encryption for Key Management Interoperability Protocol (KMIP) servers that only support KMIP protocol version 1.0 or 1.1.

This parameter is only available at startup. To set the parameter, use the setParameter setting.

The following example sets auditEncryptKeyWithKMIPGet to true:

mongod --setParameter auditEncryptKeyWithKMIPGet=true

Transaction Parameters

AbortExpiredTransactionsSessionCheckoutTimeout

New in version 8.1: (also available in 8.0.13)

Available for mongod only.

Type: integer

Default: 100 milliseconds

A session is checked out from a session pool to run database operations.

AbortExpiredTransactionsSessionCheckoutTimeout sets the maximum number of milliseconds for a session to be checked out when attempting to end an expired transaction.

If the expired transaction is successfully ended, MongoDB increments metrics.abortExpiredTransactions.successfulKills. If the transaction isn't successfully ended because it timed out when attempting to check out a session, MongoDB increments metrics.abortExpiredTransactions.timedOutKills.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets AbortExpiredTransactionsSessionCheckoutTimeout to 120 milliseconds:

db.adminCommand( { setParameter: 1, AbortExpiredTransactionsSessionCheckoutTimeout: 120 } )

You can also set this parameter during startup. For example:

mongod --setParameter AbortExpiredTransactionsSessionCheckoutTimeout=120

coordinateCommitReturnImmediatelyAfterPersistingDecision

New in version 5.0.

Updated in version 6.1

Available for mongod only.

Type: boolean

Default: false

When set to false, the shard transaction coordinator waits for all participating shards to acknowledge the decision to either commit or cancel a multi-document transaction before returning the result to the client.
When set to true, the shard transaction coordinator returns a multi-document transaction commit decision to the client as soon as the decision is made durable with the requested transaction write concern.
If the client requested a write concern that is less than "majority", the commit may roll back after the decision is returned to the client.
Transactions may not have "read your writes" consistency. That is, a read operation may not show the results of write operations that preceded it. This can happen if:
- A transaction has to write to multiple shards.
- The read and the earlier write take place in different sessions.
Causal consistency only guarantees the causal relationship of reads and writes that occur within the same session.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets coordinateCommitReturnImmediatelyAfterPersistingDecision to true:

mongod --setParameter coordinateCommitReturnImmediatelyAfterPersistingDecision=true

During run time, you can also set the parameter with the setParameter command:

db.adminCommand( { setParameter: 1, coordinateCommitReturnImmediatelyAfterPersistingDecision: true } )

internalSessionsReapThreshold

New in version 6.0.

Available for both mongod and mongos.

Default: 1000

Session limit for internal session metadata deletion. The metadata:

Contains session transaction information for user operations.
Is stored in the config.transactions collection.

When the number of internal sessions is greater than internalSessionsReapThreshold, the metadata is deleted.

If you set internalSessionsReapThreshold to 0, the internal session metadata is only deleted when the user session ends.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following example sets internalSessionsReapThreshold to 500 sessions:

db.adminCommand( { setParameter: 1, internalSessionsReapThreshold: 500 } )

You can also set internalSessionsReapThreshold at startup. For example:

mongod --setParameter internalSessionsReapThreshold=500

transactionLifetimeLimitSeconds

Available for mongod only.

Default: 60

Specifies the lifetime of multi-document transactions. Transactions that exceed this limit are considered expired and will be aborted by a periodic cleanup process. The cleanup process runs every transactionLifetimeLimitSeconds/2 seconds or at least once every 60 seconds.

The cleanup process helps relieve storage cache pressure.

The minimum value for transactionLifetimeLimitSeconds is 1 second.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the transactionLifetimeLimitSeconds to 30 seconds:

db.adminCommand( { setParameter: 1, transactionLifetimeLimitSeconds: 30 } )

You can also set parameter transactionLifetimeLimitSeconds at startup time.

mongod --setParameter "transactionLifetimeLimitSeconds=30"

To set the parameter for a sharded cluster, the parameter must be modified for all shard replica set members.

Starting in MongoDB 5.0, if you change the transactionLifetimeLimitSeconds parameter, you must also change transactionLifetimeLimitSeconds to the same value on all config server replica set members. Keeping this value consistent:

Ensures the routing table history is retained for at least as long as the transaction lifetime limit on the shard replica set members.
Reduces the transaction retry frequency and therefore improves performance.

transactionTooLargeForCacheThreshold

New in version 6.2.

Available for mongod only.

Type: decimal

Default: 0.75

The threshold value for retrying transactions that fail due to cache pressure. The value is a percentage of the dirty cache size. The default value, 0.75, means 75% of the dirty cache.

The dirty cache is limited to 20% of the total cache size. When transactionTooLargeForCacheThreshold is set to 0.75, the server only retries transactions that use less than 15% (0.75 * 20%) of the total storage engine cache.

The limit only applies to retries. Large transactions can use more than transactionTooLargeForCacheThreshold percent of the dirty cache. However, if a large transaction is rolled back due to cache pressure, the server issues a TransactionTooLargeForCache error and does not retry the transaction.

To disable this behavior, set transactionTooLargeForCacheThreshold to 1.0.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

For more information on WiredTiger storage, see: storage.wiredTiger Options.

maxTransactionLockRequestTimeoutMillis

Available for mongod only.

Type: integer

Default: 5

The maximum amount of time in milliseconds that multi-document transactions should wait to acquire locks required by the operations in the transaction.

If the transaction cannot acquire the locks after waiting maxTransactionLockRequestTimeoutMillis, the transaction aborts.

By default, multi-document transactions wait 5 milliseconds. That is, if the transaction cannot acquire the locks within 5 milliseconds, the transaction aborts. If an operation provides a greater timeout in a lock request, maxTransactionLockRequestTimeoutMillis overrides the operation-specific timeout.

You can set maxTransactionLockRequestTimeoutMillis to:

0 such that if the transaction cannot acquire the required locks immediately, the transaction aborts.
A number greater than 0 to wait the specified time to acquire the required locks. This can help obviate transaction aborts on momentary concurrent lock acquisitions, like fast-running metadata operations. However, this could possibly delay the abort of deadlocked transaction operations.
-1 to use the operation specific timeout.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following sets the maxTransactionLockRequestTimeoutMillis to 20 milliseconds:

db.adminCommand( { setParameter: 1, maxTransactionLockRequestTimeoutMillis: 20 } )

You can also set this parameter during start-up:

mongod --setParameter maxTransactionLockRequestTimeoutMillis=20

Slot-Based Execution Parameters

planCacheSize

New in version 6.3.

Available for mongod only.

Type: string

Default: 5%

Note

Although the planCacheSize parameter existed in prior versions of MongoDB, it had no effect on the plan cache until version 6.3.

Sets the size of the plan cache only for the slot-based query execution engine.

You can set the planCacheSize value to either:

A percentage of the system's total physical memory to allocate for the plan cache. For example, "8.5%".
The exact amount of data to allocate for the plan cache in either MB or GB. For example, "100MB" or "1GB".

Increasing the plan cache size adds more cached plan cache query shapes for the query planner. This can improve query performance, but increases memory usage.

This parameter is available both at runtime and at startup:

To set the parameter at runtime, use the setParameter command.
To set the parameter at startup, use the setParameter setting.

The following startup command sets planCacheSize to 80 megabytes:

mongod --setParameter planCacheSize="80MB"

You can also use the setParameter command within the MongoDB Shell:

db.adminCommand( { setParameter: 1, planCacheSize: "80MB" } )

Back

Configuration File Settings and Command-Line Options Mapping

MongoDB Cluster Parameters