Nosql Mongodb之旅(23)—MongoDB Replica oplog

主从操作日志oplog

MongoDB的Replica Set架构是通过一个日志来存储写操作的，这个日志就叫做"oplog"。oplog.rs是一个固定长度的capped collection,它存在于"local"数据库中，用于记录Replica Sets操作日志。在默认情况下，对于64位的MongoDB,oplog是比较大的，可以达到5%的磁盘空间。oplog的大小是可以通过mongod的参数“--oplogSize”来设置。

[plain]view plaincopy

1. rs1:PRIMARY>uselocal@H_502_29@
2. switchedtodblocal@H_502_29@
3. rs1:PRIMARY>showcollections@H_502_29@
4. oplog.rs@H_502_29@
5. system.replset@H_502_29@
6. rs1:PRIMARY>db.oplog.rs.find()@H_502_29@
7. {"ts":{"t":1338457763000,"i":1},"h":NumberLong(0),"op":"n","ns":"","o":{"msg":@H_502_29@
8. "initiatingset"}}@H_502_29@
9. {"ts":{"t":1338459114000,"h":NumberLong("5493127699725549585"),"op":"i",@H_502_29@
10. "ns":"test.c1","o":{"_id":ObjectId("4fc743e9aea289af709ac6b5"),"age":29,"name":@H_502_29@
11. "Tony"}}@H_502_29@
12. rs1:PRIMARY>@H_502_29@

字段说明

ts: 某个操作的时间戳

op: 操作类型，如下：
 i: insert
 d: delete
 u: update

ns: 命名空间，也就是操作的collection name

o: document 的内容

查看master 的oplog 元数据信息：

[plain]view plaincopy

1. rs1:PRIMARY>db.printReplicationInfo()@H_502_29@
2. configuredoplogsize:47.6837158203125MB@H_502_29@
3. loglengthstarttoend:1351secs(0.38hrs)@H_502_29@
4. oplogfirsteventtime:ThuMay31201217:49:23GMT+0800(CST)@H_502_29@
5. oploglasteventtime:ThuMay31201218:11:54GMT+0800(CST)@H_502_29@
6. Now:ThuMay31201218:21:58GMT+0800(CST)@H_502_29@
7. rs1:PRIMARY>@H_502_29@

configured oplog size: 配置的oplog 文件大小

log length start to end: oplog 日志的启用时间段

oplog first event time: 第一个事务日志的产生时间

oplog last event time: 最后一个事务日志的产生时间

Now: 现在的时间

查看slave 的同步状态

[plain]view plaincopy

1. rs1:PRIMARY>db.printSlaveReplicationInfo()@H_502_29@
2. source:localhost:28011@H_502_29@
3. syncedTo:ThuMay31201218:11:54GMT+0800(CST)@H_502_29@
4. =884secsago(0.25hrs)@H_502_29@
5. source:localhost:28012@H_502_29@
6. syncedTo:ThuMay31201218:11:54GMT+0800(CST)@H_502_29@
7. =884secsago(0.25hrs)@H_502_29@
8. rs1:PRIMARY>@H_502_29@

字段说明

source: 从库的IP 及端口

syncedTo: 目前的同步情况，延迟了多久等信息

主从配置信息

在local库中不仅有主从日志oplog集合，还有一个集合用于记录主从配置信息，即：system.replset

[plain]view plaincopy

1. rs1:PRIMARY>db.system.replset.find()@H_502_29@
2. {"_id":"rs1","version":1,"members":[@H_502_29@
3. {@H_502_29@
4. "_id":0,108); list-style:decimal-leading-zero outside; line-height:21px; margin:0px!important; padding:0px 3px 0px 10px!important"> "host":"localhost:28010"@H_502_29@
5. },108); list-style:decimal-leading-zero outside; line-height:21px; margin:0px!important; padding:0px 3px 0px 10px!important"> "_id":1,108); list-style:decimal-leading-zero outside; line-height:21px; margin:0px!important; padding:0px 3px 0px 10px!important"> "host":"localhost:28011"@H_502_29@
6. "_id":2,108); list-style:decimal-leading-zero outside; line-height:21px; margin:0px!important; padding:0px 3px 0px 10px!important"> "host":"localhost:28012"@H_502_29@
7. }@H_502_29@
8. ]}@H_502_29@
9. rs1:PRIMARY>@H_502_29@

从这个集合中可以看出，Replica Sets 的配置信息，也可以在任何一个成员实例上执行rs.conf()来查看配置信息。