MongoDB gives us the fsync+lock mechanism to put data violence on the hard drive

Can the data violence to the hard disk, of course, is possible, MongoDB provides us with a fsync+lock mechanism to meet our needs.

Fsync+lock first will buffer data violence into the hard disk, and then a write lock to the database, the other instances of the write operations are all blocked until Fsync

+lock Release the lock.

It's not going to be tested here.

Locking: Db.runcommand ({"Fsync": 1, "Lock": 1})

Release Lock: Db. $cmd. Unlock.findone ()

Fsync

Forces the mongod process to flush all pending writes from the storage layer to disk. Optionally, you can use to fsync 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 interval, which is a seconds by default. Run when you fsync want to flush writes to disk ahead of the that interval.

The fsync command has the following syntax:

Fsync1Async<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.

Examplesrun asynchronously

The fsync operation is synchronous by default. To run fsync asynchronously with the async field set to true :

Fsync1Async}  

The operation returns immediately. fsyncto view the status of the operation, check the output of db.currentOp() .

Lock mongodInstance

NOTE

Changed in version 3.2: fsync command with the lock option can ensure that the data files does not change for MongoDB Insta NCEs using either the MMAPV1 or the Wiredtiger storage engines, thus providing consistency for the purposes of creating BA Ckups.

In previous MongoDB versions, fsync command with the lock option cannot guarantee a consistent set of files for Low-level backups (e.g. via file copy cp , scp , tar ) for Wiredtiger.

The primary use of was to lock the instance in order-to-back up the fsync mongod files within mongod ' s dbPath . The operation flushes all data to the storage layer and blocks all write operations until you unlock the mongod instance.

To lock the database, with the lock field set to true :

Fsync1lock}  

You could continue to perform read operations on a mongod instance it has a fsync lock. However, after the first write operation all subsequent read operations wait until you unlock the mongod instance.

Unlock mongodInstance

mongodto unlock the, use db.fsyncUnlock() :

DB.  Fsyncunlock();  

See: https://docs.mongodb.com/manual/reference/command/fsync/

MongoDB gives us the fsync+lock mechanism to put data violence on the hard drive