Forces the mongod process to flush all pending writes from the storage layer to disk. Optionally, you can use fsync to lock the mongod instance and block write operations for the purpose of capturing backups.

As applications write data, MongoDB records the data in the storage layer and then writes the data to disk within the syncPeriodSecs interval, which is 60 seconds by default. Run fsync when you want to flush writes to disk ahead of that interval.

The fsync command has the following syntax:

{ fsync: 1, async: <Boolean>, lock: <Boolean> } 

The fsync command has the following fields:

Field	Type	Description
fsync	integer	Enter “1” to apply fsync.
async	boolean	Optional. Runs fsync asynchronously. By default, the fsync operation is synchronous.
lock	boolean	Optional. Locks mongod instance and blocks all write operations.

Examples

{ fsync: 1, async: true } 

{ fsync: 1, lock: true } 

db.fsyncUnlock();