Shulou(Shulou.com)06/01 Report--

Recently, I have been developing with mongodb. On linux, it is customary to use kill-9 PID to shut down the service.

As a result, every time you shut down and restart mongodb, mongodb always shuts down itself. Look at the log also did not see what to come, and then Baidu.

It is found that the consequences of killing mongodb with kill-9 are quite serious.

Then I went to the official website to check it out.

MongoDB uses a memory-mapped storage engine:

It converts disk IO operations into memory operations, if it is a read operation, the data in memory acts as a cache, and if it is a write operation, memory can also convert random write operations into sequential write operations, which can greatly improve performance.

The write operation is flush to disk every 60 seconds (set by syncdelay). If the flush is stopped within these 60 seconds and we do kill-9, then all write data since the last flush will be lost.

If you execute kill-9 while the flush operation is in progress, it will cause file confusion and may result in the loss of all data.

Official description:

Sending a KILL signal kill-9 will probably cause damage as mongod will not be able to cleanly exit. In such a scenario, run the repairDatabase command.

Fortunately, I found it early. Otherwise, there may be some accident.

Finally, it is found that mongodb can be turned off in the following ways

1. Use killall mongod

2. Use kil-15 PID

3. Execute the db.shutdownServer () command under the admin user

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