compact
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Definition
compactRewrites and defragments all data and indexes in a collection. On WiredTiger databases, this command will release unneeded disk space to the operating system.
compacthas the following form:{ compact: <collection name> } compacttakes the following fields:Note
Starting in MongoDB 4.2
MongoDB removes the MMAPv1 storage engine and the MMAPv1 specific options
paddingFactor,paddingBytes,preservePaddingforcompact.FieldTypeDescriptioncompactstringThe name of the collection.forceflagChanged in version 4.4.
Optional. Starting in v4.4, if specified, forces
compactto run on the primary in a replica set. Before v4.4, this boolean field enabledcompactto run on the primary in a replica set if the value wastrueand returned an error when run on a primary if the value wasfalse, because the command blocked all other operations.Starting in v4.4,
compactdoes not block MongoDB CRUD Operations on the database it is compacting.commentanyOptional. A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations:
mongod log messages, in the
attr.command.cursor.commentfield.Database profiler output, in the
command.commentfield.currentOpoutput, in thecommand.commentfield.
A comment can be any valid BSON type (string, integer, object, array, etc).
New in version 4.4.
Warning
Always have an up-to-date backup before performing server
maintenance such as the compact operation.
compact Required Privileges
For clusters enforcing authentication,
you must authenticate as a user with the compact privilege
action on the target collection. The dbAdmin role provides
the required privileges for running compact against
non-system collections.
For system collections, create a
custom role that grants the compact action on the system
collection. You can then grant that role to a new or existing user and
authenticate as that user to perform the compact command.
For example, the following operations create a custom role that grants
the compact action against specified database and
collection:
use admin db.createRole( { role: "myCustomCompactRole", privileges: [ { resource: { "db" : "<database>" , "collection" : "<collection>" }, actions: [ "compact" ] } ], roles: [] } )
For more information on configuring the resource document, see
Resource Document.
To add the dbAdmin or the custom role to an existing
user, use db.grantRolesToUser() or db.updateUser().
The following operation grants the custom compact role to the
myCompactUser on the admin database:
use admin db.grantRolesToUser("myCompactUser", [ "dbAdmin" | "myCustomCompactRole" ] )
To add the dbAdmin or the custom role to a new user,
specify the role to the roles array of the
db.createUser() method when creating the user.
use admin db.createUser( { user: "myCompactUser", pwd: "myCompactUserPassword", roles: [ { role: "dbAdmin", db: "<database>" } | "myCustomCompactRole" ] } )
Behavior
Blocking
Changed in version 4.4.
Starting in v4.4, on WiredTiger,
compact only blocks the following metadata operations:
compact does not block MongoDB CRUD Operations for the database it is
currently operating on.
Before v4.4, compact blocked all operations for the
database it was compacting, including MongoDB CRUD Operations, and was therefore
recommended for use only during scheduled maintenance periods. Starting in
v4.4, the compact command is appropriate for use at any time.
You may view the intermediate progress either by viewing the
mongod log file or by running the
db.currentOp() in another shell instance.
Operation Termination
If you terminate the operation with the db.killOp() method or restart the server before the
compact operation has finished, be aware of the following:
If you have journaling enabled, the data remains valid and usable, regardless of the state of the
compactoperation. You may have to manually rebuild the indexes.If you do not have journaling enabled and the
mongodorcompactterminates during the operation, it is impossible to guarantee that the data is in a valid state.In either case, much of the existing free space in the collection may become un-reusable. In this scenario, you should rerun the compaction to completion to restore the use of this free space.
Disk Space
To see how the storage space changes for the collection, run the
collStats command before and after compaction.
On WiredTiger, compact attempts to
reduce the required storage space for data and indexes in a collection, releasing
unneeded disk space to the operating system. The effectiveness of this operation
is workload dependent and no disk space may be recovered. This command is useful
if you have removed a large amount of data from the collection, and do not plan
to replace it.
compact may require additional disk space to run on WiredTiger databases.
Replica Sets
compact commands do not replicate to secondaries in a
replica set.
Compact each member separately.
Ideally run
compacton a secondary. See optionforceabove for information regarding compacting the primary.Starting in MongoDB 5.0.3 (and 4.4.9 and 4.2.18): a secondary is not available when
compactis running. The secondary does not enter theRECOVERINGstate.For previous MongoDB versions: on secondaries,
compactforces the secondary to enter theRECOVERINGstate. Read operations issued to an instance in theRECOVERINGstate will fail. This prevents clients from reading during the operation. When the operation completes, the secondary returns toSECONDARYstate.
See Replica Set Member States for more information about replica set member states.
See Perform Maintenance on Replica Set Members for an example replica set maintenance procedure to maximize availability during maintenance operations.
Sharded Clusters
compact only applies to mongod instances. In a
sharded environment, run compact on each shard separately
as a maintenance operation.
Capped Collections
On WiredTiger, the compact
command will attempt to compact the collection.
Index Building
mongod rebuilds all indexes in parallel following the
compact operation.