分享MongoDB修改oplog大小的4种方法

分享MongoDB修改oplog大小的4种方法

目录

方法一

方法二

方法三

1.关闭mongod

2.修改配置文件

3.启动mongod实例,并备份oplog

4.重建oplog

5.插入前面保存的oplog时间点记录

6.关闭mongod实例

方法四

1.查看oplog大小

2.修改oplog大小

3.验证oplog大小

4.整理碎片,回收空间(可选)

修改oplog有四种方法:

方法一

步骤如下:

停掉所有secondary节点

主节点删除local目录下文件,副本节点删除数据目录下所有文件

修改所有节点的配置文件,如:oplogSize=1000

重启所有节点,包括主节点和副本节点

重新配置replca set,副本节点会重新同步数据(initial sync)

优点:操作简单。
缺点:需要停服务,若数据量大,数据同步代价高。

方法二

步骤如下:

remove其中一个secondary节点,并关闭mongod服务,删除数据目录下所有文件

修改此节点的参数文件,如:oplogSize=1000,并启动mongod服务

在primary节点执行rs.add()将此节点加入到replica set

循环1-3步骤,将所有副本节点全部改完

primary节点执行rs.stepDown()将主节点降级为副本节点

从新的主节点remove掉此节点,并进行步骤1-3
这样逐个修改每个节点,完成oplog修改。

优点:解决了方法一中的停机问题。
缺点:每个节点都要逐个重新同步,时间代价更高。

方法三

The oplog exists internally as a capped collection, so you cannot modify its size in the course of normal operations.另:改变oplog大小,需要在每个节点上执行维护模式。(官方推荐)

1.关闭mongod

关闭mongod实例,如果是primary节点,执行rs.stepDown() 降级

handong1:PRIMARY> rs.stepDown() { "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1619693040, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1619693040, 1) } handong1:SECONDARY> handong1:SECONDARY> handong1:SECONDARY> handong1:SECONDARY> use admin switched to db admin handong1:SECONDARY> db.shutdownServer() 2021-04-29T18:44:33.947+0800 I NETWORK [js] DBClientConnection failed to receive message from 127.0.0.1:27017 - HostUnreachable: Connection closed by peer server should be down... 2021-04-29T18:44:33.950+0800 I NETWORK [js] trying reconnect to 127.0.0.1:27017 failed 2021-04-29T18:44:33.967+0800 I NETWORK [js] reconnect 127.0.0.1:27017 failed failed 2.修改配置文件

修改配置文件,修改端口,注释掉replSet和认证相关的设置

port=27018 fork=true journal = true maxConns=500 logappend=true directoryperdb=true dbpath=/mongodb/data logpath=/mongodb/logs/mongodb.log 3.启动mongod实例,并备份oplog mongod -f /mongodb/conf/mongodb.conf about to fork child process, waiting until server is ready for connections. forked process: 31553 child process started successfully, parent exiting mongodump -d local -c oplog.rs --port 27018 -h 172.16.254.134 -o /mongodb/backup 2021-04-29T18:55:18.167+0800writing local.oplog.rs to /mongodb/backup/local/oplog.rs.bson 2021-04-29T18:55:18.170+0800done dumping local.oplog.rs (798 documents) 4.重建oplog

保存oplog最新时间点

> use local switched to db local > db.temp.save( db.oplog.rs.find( { }, { ts: 1, h: 1 } ).sort( {$natural : -1} ).limit(1).next() ) WriteResult({ "nInserted" : 1 }) > db.temp.find() { "_id" : ObjectId("608a914089abaa981f14e888"), "ts" : Timestamp(1619693066, 1), "h" : NumberLong(0) }

删除旧的oplog

db.oplog.rs.drop()

重建新的oplog,大小为2GB

> db.runCommand( { create: "oplog.rs", capped: true, size: (2 * 1024 * 1024 * 1024) } ) 5.插入前面保存的oplog时间点记录 > db.oplog.rs.save( db.temp.findOne() ) > db.oplog.rs.find() 6.关闭mongod实例 > use admin switched to db admin > db.shutdownServer() 2021-04-29T19:06:53.745+0800 I NETWORK [js] DBClientConnection failed to receive message from 127.0.0.1:27018 - HostUnreachable: Connection closed by peer server should be down... 2021-04-29T19:06:53.749+0800 I NETWORK [js] trying reconnect to 127.0.0.1:27018 failed 2021-04-29T19:06:53.749+0800 I NETWORK [js] reconnect 127.0.0.1:27018 failed failed

最后恢复mongodb.conf到初始状态,启动

方法四

如果你的MongoDB版本为4.0以后的版本,可以直接使用replSetResizeOplog修改。

1.查看oplog大小 handong1:SECONDARY> db.getReplicationInfo() { "logSizeMB" : 1000, "usedMB" : 0.17, "timeDiff" : 6736, "timeDiffHours" : 1.87, "tFirst" : "Thu Apr 29 2021 17:19:14 GMT+0800 (CST)", "tLast" : "Thu Apr 29 2021 19:11:30 GMT+0800 (CST)", "now" : "Thu Apr 29 2021 19:11:42 GMT+0800 (CST)" } 2.修改oplog大小 handong1:SECONDARY> db.adminCommand({replSetResizeOplog:1,size:2000}) { "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1619694744, 14), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1619694744, 14) } 3.验证oplog大小 handong1:SECONDARY> db.getReplicationInfo() { "logSizeMB" : 2000, "usedMB" : 0.18, "timeDiff" : 6852, "timeDiffHours" : 1.9, "tFirst" : "Thu Apr 29 2021 17:19:14 GMT+0800 (CST)", "tLast" : "Thu Apr 29 2021 19:13:26 GMT+0800 (CST)", "now" : "Thu Apr 29 2021 19:13:28 GMT+0800 (CST)" } 4.整理碎片,回收空间(可选) handong1:SECONDARY> use local switched to db local handong1:SECONDARY> db.runCommand({"compact" : "oplog.rs"}) { "ok" : 1, "$clusterTime" : { "clusterTime" : Timestamp(1619694840, 1), "signature" : { "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId" : NumberLong(0) } }, "operationTime" : Timestamp(1619694840, 1) }

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