mongodb给咱们提供了fsync+lock机制把数据暴力的刷到硬盘上

时间 2019-12-01

标签 mongodb 咱们提供 fsync+lock fsync lock 机制数据硬盘栏目 MongoDB 繁體版

原文原文链接

能不能把数据暴力的刷到硬盘上，固然是能够的,mongodb给咱们提供了fsync+lock机制就能知足咱们提的需求。javascript

fsync+lock首先会把缓冲区数据暴力刷入硬盘，而后给数据库一个写入锁，其余实例的写入操做所有被阻塞，直到fsyncjava

+lock释放锁为止。mongodb

这里就不测试了。数据库

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

释放锁： db.$cmd.unlock.findOne()async

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.测试

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.spa

The fsync command has the following syntax:code

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

The fsync command has the following fields:orm

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();  
   

mongodb给咱们提供了fsync+lock机制把数据暴力的刷到硬盘上

fsync

Examples

Run Asynchronously

Lock mongod Instance

Unlock mongod Instance

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

Lock `mongod` Instance

Unlock `mongod` Instance