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• Definition
• Examples

Definition

fsyncUnlock

Reduces the lock taken by fsync (with the lock option) on a mongod instance by 1.

Important

The fsync lock and fsyncUnlock operations maintain a lock count. Each fsync lock operation increments the lock count, and fsyncUnlock decrements the lock count.

To unlock a mongod instance for writes, the lock count must be zero. That is, for a given number of fsync lock operations, you must issue a corresponding number of fsyncUnlock operations to unlock the instance for writes.

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

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

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db.adminCommand( { fsyncUnlock: 1 } )

The operation returns a document with the following fields:

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.

Tip

The mongo shell provides the helper method db.fsyncUnlock().

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.