mongodb給咱們提供了fsync+lock機制把數據暴力的刷到硬盤上

能不能把數據暴力的刷到硬盤上，固然是能夠的,mongodb給咱們提供了fsync+lock機制就能知足咱們提的需求。

fsync+lock首先會把緩衝區數據暴力刷入硬盤，而後給數據庫一個寫入鎖，其餘實例的寫入操做所有被阻塞，直到fsync

+lock釋放鎖爲止。

這裏就不測試了。

 加鎖：    db.runCommand({"fsync":1,"lock":1})

 釋放鎖： db.$cmd.unlock.findOne()

 

fsync

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

Run Asynchronously

The fsync operation is synchronous by default. To run fsync asynchronously, use the async field set totrue:

{ fsync: 1, async: true } 

The operation returns immediately. To view the status of the fsync operation, check the output ofdb.currentOp().

Lock mongod Instance

NOTE

Changed in version 3.2: fsync command with the lock option can ensure that the data files do not change for MongoDB instances using either the MMAPv1 or the WiredTiger storage engines, thus providing consistency for the purposes of creating backups.

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 fsync is to lock the mongod instance in order to back up the files within mongod‘sdbPath. The operation flushes all data to the storage layer and blocks all write operations until you unlock themongod instance.

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

{ fsync: 1, lock: true } 

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

Unlock mongod Instance

To unlock the mongod, use db.fsyncUnlock():

db.fsyncUnlock(); 

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