MongoDB主从模式如何修改主库的oplogsize，相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

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如果是集群分片环境建议使用官方方法：

https://docs.mongodb.com/v3.0/tutorial/change-oplog-size/

这里环境是传统的master/slave，并没有使用replicate set，而且后期版本mongodb将废弃m/s，如果是单实例或者传统m/s的结构，修改oplogsize只需删除local库即可，操作记录如下：

先关闭master和auth功能

[root@fogtestdb data]# vi /etc/mongodb.cnf

dbpath = /mongodb/data

logpath = /var/log/mongodb/mongodb.log

pidfilepath = /var/run/mongodb/mongodb.pid

logappend = true

port = 27017

fork = true

#master = true

maxConns=2048

noprealloc = true

httpinterface = true

oplogSize=1024

#auth=true

#keyFile = /etc/mongo.key

重启mogodb

[root@fogtestdb data]# mongod -f /etc/mongodb.cnf --shutdown

note: noprealloc may hurt performance in many applications

killing process with pid: 4749

[root@fogtestdb data]# mongod -f /etc/mongodb.cnf &

删除local库

[root@mongodb ~] # mongo

> use local

> db.dropDatabase()

修改oplogsize大小并启动mongodb

[root@fogtestdb data]# vi /etc/mongodb.cnf

dbpath = /mongodb/data

logpath = /var/log/mongodb/mongodb.log

pidfilepath = /var/run/mongodb/mongodb.pid

logappend = true

port = 27017

fork = true

master = true

maxConns=2048

noprealloc = true

httpinterface = true

oplogSize=20480

auth=true

keyFile = /etc/mongo.key

重启mongodb

[root@fogtestdb data]# mongod -f /etc/mongodb.cnf --shutdown

[root@fogtestdb data]# mongod -f /etc/mongodb.cnf &

[1] 4802

[root@fogtestdb data]# note: noprealloc may hurt performance in many applications

about to fork child process, waiting until server is ready for connections.

forked process: 4804

child process started successfully, parent exiting

[1]+  Done                    mongod -f /etc/mongodb.cnf

登入查看oplogsize

[root@fogtestdb data]# mongo 127.0.0.1:27017/admin -uroot -ptest

MongoDB shell version: 3.2.0

connecting to: 127.0.0.1:27017/admin

Server has startup warnings:

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten]

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten] ** WARNING: The server is started with the web server interface and access control.

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten] **          The web interfaces (rest, httpinterface and/or jsonp) are insecure

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten] **          and should be disabled unless required for backward compatibility.

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended.

2017-02-22T14:52:04.246+0800 I CONTROL  [initandlisten]

>

查看oplog大小

> db.printReplicationInfo()

configured oplog size: 20480MB

log length start to end: 624021secs (173.34hrs)

oplog first event time:  Fri Feb 10 2017 10:24:16 GMT+0800 (CST)

oplog last event time:   Fri Feb 17 2017 15:44:37 GMT+0800 (CST)

now:                     Fri Feb 17 2017 15:44:47 GMT+0800 (CST)

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