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

Complain about Mongodb. Recently, we often talk about Mongodb in the group. I also think of the tough days of operating and maintaining it (2.0.4). Here I complain and make an impression:

1. Without a root proprietary connection, you can only try your luck a few times when the Mongodb connection is full. No wonder you have encountered the use of mongos+replicatset; if you use Javaclient, you can set connectionsPerHost (10) and threadsAllowedToBlockForConnectionMultiplier (5).

two。 Global lock VS read-write separation; before 2.2, the read-write separation of Mongodb is actually a bit of a decoration, how to say, when the pressure of secondary reading is high, it also blocks the writing of oplog, which leads to master-slave delay, and then Out of sync; or replication will also block the read of slave library, and this problem is not solved until 2.2.

3.Mongos memory leak. I don't know if it has been solved now. At that time, it was an automatic script restart.

4.Query Optimizer is stupid; count (*) with overlay index takes table scan instead of index cover scan

5. Double the write pressure: due to the separation of JournalLog and oplog, a replicaset master will produce 3 copies (after compression and other optimization seems to be 2.5 times), for the IO boundless type but can not turn off the JounalLog to adjust the flushinterval effect is obvious

6.Rename collection will crash mongod

7. I still remember that when I first took over mongodb, I accidentally removeshard (it takes N days to calculate the time), but luckily I stopped draining in time.

8. Need to learn OS memory, cache management

9....

To complain, there must be a lot of immaturity in the original operation and maintenance of Mongodb, if you still dare to use it, three words: look at the scene.

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