mongodb给我们提供了fsync+lock机制把数据暴力的刷到硬盘上

能不能把数据暴力的刷到硬盘上，当然是可以的,mongodb给我们提供了fsync+lock机制就能满足我们提的需求。

fsync+lock首先会把缓冲区数据暴力刷入硬盘，然后给数据库一个写入锁，其他实例的写入操作全部被阻塞，直到fsync

+lock释放锁为止。

这里就不测试了。

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

释放锁： 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 to

true

:

{ fsync: 1, async: true }

The operation returns immediately. To view the status of the

fsync

operation, check the output of

db.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

‘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, 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();

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