fsyncUnlock

Definition

fsyncUnlock

Reduces the lock count on the server or cluster. To enable write operations, the lock count must be zero.

Starting in MongoDB 4.4.25, the fsync and fsyncUnlock commands can run on mongos to lock and unlock a sharded cluster.

Use this command to unblock writes after you finish a backup operation.

Important

Servers maintain an fsync lock count. The fsync command with the lock field set to true increments the lock count while the fsyncUnlock command decrements it. To enable writes on a locked server or cluster, call the fsyncUnlock command until the lock count reaches zero.

fsyncUnlock is an administrative operation. Typically you will use fsyncUnlock following a database backup operation.

Tip

In the mongo Shell, this command can also be run through the db.fsyncUnlock() helper method.

Helper methods are convenient for mongo users, but they may not return the same level of information as database commands. In cases where the convenience is not needed or the additional return fields are required, use the database command.

To run the fsyncUnlock command, use the db.adminCommand() method:

db.adminCommand(
   {
     fsyncUnlock: 1,
     comment: <any>
   }
)

The comment field is optional and may contain a comment of any data type.

The operation returns a document with the following fields:

Field	Description
info	Information on the status of the operation
lockCount (New in version 3.4)	The number of locks remaining on the instance after the operation.
ok	The status code.

Examples

Consider a situation where db.fsyncLock() has been issued two times. The following fsyncUnlock operation reduces the locks taken by db.fsyncLock() by 1:

db.adminCommand( { fsyncUnlock: 1 } )

The operation returns the following document:

{ "info" : "fsyncUnlock completed", "lockCount" : NumberLong(1), "ok" : 1 }

As the lockCount is greater than 0, the mongod instance is locked against writes. To unlock the instance for writes, run the unlock operation again:

db.adminCommand( { fsyncUnlock: 1 } )

The operation returns the following document:

{ "info" : "fsyncUnlock completed", "lockCount" : NumberLong(0), "ok" : 1 }

The mongod instance is unlocked for writes.