setFeatureCompatibilityVersion
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Definition
setFeatureCompatibilityVersion
Enables or disables the features that persist data incompatible with earlier versions of MongoDB. You can only issue the
setFeatureCompatibilityVersion
against theadmin
database.
Syntax
The command takes the following form:
db.adminCommand( { setFeatureCompatibilityVersion: <version>, writeConcern: { wtimeout: <timeout> } } )
The values for the version
are:
Version | Description |
---|---|
"4.4" | Available on MongoDB 4.4 Deployments Enables the 4.4 features that persist data incompatible with MongoDB 4.2. Enabling these backwards-incompatible features can complicate the downgrade process since you must remove any persisted backwards-incompatible features before you downgrade. It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features. |
"4.2" | Available on MongoDB 4.2 and 4.4 Deployments Enables the 4.2 features that persist data incompatible with MongoDB 4.0. Enabling these backwards-incompatible features can complicate the downgrade process since you must remove any persisted backwards-incompatible features before you downgrade. It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features.
|
"4.0" | Available on MongoDB 4.0 and 4.2 Deployments
|
"3.6" | Available on MongoDB 3.6 and 4.0 Deployments
|
"3.4" | Available on MongoDB 3.4 and MongoDB 3.6 Deployments
|
"3.2" | Available on MongoDB 3.4 Deployments Disables the 3.4 features that persist data incompatible with MongoDB 3.2. |
The optional writeConcern
specifies the write concern
wtimeout
value in milliseconds:
The time period that the primary waits for acknowledgment from the majority of the replica set members. If the acknowledgment is not received in the time period, the operation fails.
Default is
60000
milliseconds. Use a longer time period if the secondary members of the replica set have a delay that exceeds thewtimeout
default.
Behavior
Conflicts with Background Operations
Certain background operations may prevent
execution of setFeatureCompatibilityVersion
. Use
currentOp
to identify any ongoing operations.
Default Values
Deployments | featureCompatibilityVersion |
---|---|
For new 4.4 deployments | "4.4" |
For 4.4 deployments upgraded from 4.2 | "4.2" until you setFeatureCompatibilityVersion to "4.4" . |
For new 4.2 deployments | "4.2" |
For 4.2 deployments upgraded from 4.0 | "4.0" until you setFeatureCompatibilityVersion to "4.2" . |
For new 4.0 deployments | "4.0" |
For 4.0 deployments upgraded from 3.6 | "3.6" until you setFeatureCompatibilityVersion to "4.0" . |
For new 3.6 deployments | "3.6" |
For 3.6 deployments upgraded from 3.4 | "3.4" until you setFeatureCompatibilityVersion
to "3.6" . |
For new 3.4 deployments | "3.4" |
For 3.4 deployments upgraded from 3.2 | "3.2" until you setFeatureCompatibilityVersion
to "3.4" . |
Idempotency
This command must perform writes to an internal system collection. If for any reason the command does not complete successfully, you can safely retry the command as the operation is idempotent.
Feature Compatibility in Arbiters
Arbiters do not replicate the admin.system.version
collection.
Because of this, arbiters always have a Feature Compatibility Version equal
to the downgrade version of the binary, regardless of the FCV value of the
replica set.
For example, an arbiter in a MongoDB 4.4 cluster, has an FCV value of 4.2.
Examples
View FeatureCompatibilityVersion
To view the featureCompatibilityVersion
for a mongod
instance, run the following command on a mongod
instance:
Note
The operation is undefined on the mongos
instances. For a
sharded cluster that has access control enabled, to run the command
against a member of the shard replica set, you must connect to the
member as a shard local user.
db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
In the results document, the format of the
featureCompatibilityVersion
depends on the MongoDB version. Click
on the tab for the appropriate MongoDB version.
Set Feature Compatibility Version on MongoDB 4.4 Deployments
Set Feature Compatibility Version on MongoDB 4.2 Deployments
Set Feature Compatibility Version on MongoDB 4.0 Deployments
Set Feature Compatibility Version on MongoDB 3.6 Deployments
Set Feature Compatibility Version on MongoDB 3.4 Deployments
Set Write Concern Timeout
The following example sets the optional write concern wtimeout
field to 5000 (5 seconds).
Note
Run the setFeatureCompatibilityVersion
command against
the admin
database.
db.adminCommand( { setFeatureCompatibilityVersion: "4.4", writeConcern: { wtimeout: 5000 } } )