分享MongoDB修改oplog大小的4種方法

2022-04-10 22:00:04

方法一

步驟如下：

停掉所有secondary節點
主節點刪除local目錄下檔案，副本節點刪除資料目錄下所有檔案
修改所有節點的組態檔，如：oplogSize=1000
重啟所有節點，包括主節點和副本節點
重新設定replca set，副本節點會重新同步資料（initial sync）

優點：操作簡單。
缺點：需要停服務，若資料量大，資料同步代價高。

方法二

步驟如下：

remove其中一個secondary節點，並關閉mongod服務，刪除資料目錄下所有檔案
修改此節點的引數檔案，如：oplogSize=1000，並啟動mongod服務
在primary節點執行rs.add()將此節點加入到replica set
迴圈1-3步驟，將所有副本節點全部改完
primary節點執行rs.stepDown()將主節點降級為副本節點
從新的主節點remove掉此節點，並進行步驟1-3
這樣逐個修改每個節點，完成oplog修改。

優點：解決了方法一中的停機問題。
缺點：每個節點都要逐個重新同步，時間代價更高。

方法三

The oplog exists internally as a capped collection, so you cannot modify its size in the course of normal operations.另：改變oplog大小，需要在每個節點上執行維護模式。（官方推薦）

1.關閉mongod

關閉mongod範例，如果是primary節點，執行rs.stepDown() 降級

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.修改組態檔

修改組態檔，修改埠，註釋掉replSet和認證相關的設定

port=27018
fork=true
journal = true
maxConns=500
logappend=true
directoryperdb=true
dbpath=/mongodb/data
logpath=/mongodb/logs/mongodb.log

3.啟動mongod範例，並備份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+0800	writing local.oplog.rs to /mongodb/backup/local/oplog.rs.bson
2021-04-29T18:55:18.170+0800	done dumping local.oplog.rs (798 documents)

4.重建oplog

儲存oplog最新時間點

> 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) }

刪除舊的oplog

db.oplog.rs.drop()

重建新的oplog，大小為2GB

> db.runCommand( { create: "oplog.rs", capped: true, size: (2 * 1024 * 1024 * 1024) } )

5.插入前面儲存的oplog時間點記錄

> db.oplog.rs.save( db.temp.findOne() )
> db.oplog.rs.find()

6.關閉mongod範例

> 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

最後恢復mongodb.conf到初始狀態，啟動

方法四

如果你的MongoDB版本為4.0以後的版本，可以直接使用replSetResizeOplog修改。

1.檢視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.驗證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，回收空間（可選）

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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