MongoDB knowledge point notes

MongoDB knowledge point notes

MongoDB knowledge point notes

1. How to read data from the backup Node

The default value is not allowed. The following error is reported:

testReplSet:SECONDARY> show dbs2016-07-19T10:25:03.196+0800 E QUERY    [thread1] Error: listDatabases failed:{ "ok" : 0, "errmsg" : "not master and slaveOk=false", "code" : 13435 } 

To allow the backup node to read data, run the following command:

db.getMongo().setSlaveOk()

2. About backup Sets

1> all operations performed by the client on a single server can be sent to the master node for execution (read, write, Execute Command, create index, etc)

2> the client cannot perform write operations on the backup node.

3> by default, the client cannot read data from the backup node unless the setSlaveOk operation is performed explicitly.

4> a single server cannot be converted to a replica set. Unless the off service is reinitialized, we recommend that you configure the replica set even if there is only one server, in this way, you do not need to stop the service after adding nodes.

5> a very important concept of replica set is "majority": it is up to the majority to select the master node. The master node can continue to serve as the master node only when the majority of support is obtained, this write operation is performed when the write operation is copied to most members.

It is safe.

3. How to view the command line parameters of the server

Db. server‑lineopts ()

4. too logs chunks to print, use verbose if you want to force print

You can run the following command to view

PrintShardingStatus (db. getSisterDB ("config"), 1 );

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