Replica set 为我们提供了自动故障切换功能，这个机制是由MongoDB自己来操作的，它根据从库的优先级或者数据新鲜度（也就是最新的从主库同步数据的那个节点）来选择primary，而当以前的primary起来之后，会成为secondary ，接受新的primary 的日志。

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                                                              完整的replica sets

                                                             primary 当机

                   mongodb 会根据数据的新鲜度来选择下一个主库

接上一篇文章，搭建好了replica set，查看端口为 27018 27020两个服务的状态：

[mongodb@rac4 bin]$ ./mongo 127.0.0.1:27018

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27018/test

PRIMARY> db.isMaster();

{

        "setName" : "myset",

        "ismaster" : true,  --为主库

        "secondary" : false,

        "hosts" : [

                "10.250.7.220:27018",

                "10.250.7.220:27020",

                "10.250.7.220:27019"

        ],

        "primary" : "10.250.7.220:27018",

        "me" : "10.250.7.220:27018",

        "maxBsonObjectSize" : 16777216,

        "ok" : 1

}

PRIMARY> exit

bye

[mongodb@rac4 bin]$ ./mongo 127.0.0.1:27020

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27020/test

SECONDARY> 

SECONDARY> db.isMaster();

{

        "setName" : "myset",

        "ismaster" : false,

        "secondary" : true, --为从库

        "hosts" : [

                "10.250.7.220:27020",

                "10.250.7.220:27019",

                "10.250.7.220:27018"

        ],

        "primary" : "10.250.7.220:27018",

        "me" : "10.250.7.220:27020",

        "maxBsonObjectSize" : 16777216,

        "ok" : 1

}

PRIMARY> 手工杀掉primary 

[root@rac4 ~]# ps -ef | grep 27018 

mongodb  14826 14794  1 20:24 pts/4    00:00:05 ./mongod --dbpath /opt/mongodata/r1 --port 27018 --replSet myset --rest

mongodb  14999 14430  0 20:28 pts/2    00:00:00 ./mongo 127.0.0.1:27018

[root@rac4 ~]# kill -9 14826 14794

[root@rac4 ~]# ps -ef | grep mongodb |grep -v root

mongodb  14883 14853  1 20:26 pts/7    00:00:05 ./mongod --dbpath /opt/mongodata/r2 --port 27019 --replSet myset --rest

mongodb  14901 14548  1 20:27 pts/6    00:00:07 ./mongod --dbpath /opt/mongodata/r3 --port 27020 --replSet myset --rest

mongodb  14999 14430  0 20:28 pts/2    00:00:00 ./mongo 127.0.0.1:27018

mongodb  15102 15072  0 20:30 pts/5    00:00:00 ./mongo 127.0.0.1:27019

mongodb  15136 15106  0 20:30 pts/8    00:00:00 ./mongo 127.0.0.1:27020

[root@rac4 ~]# 

27019 端口的mongodb 输出日志显示的选择10.250.7.220 作为主库的日志记录

Mon Oct 31 20:27:59 [FileAllocator] allocating new datafile /opt/mongodata/r2/local.2, filling with zeroes...

Mon Oct 31 20:27:59 [rsHealthPoll] replSet info member 10.250.7.220:27018 is up

Mon Oct 31 20:27:59 [rsHealthPoll] replSet member 10.250.7.220:27018 is now in state SECONDARY

Mon Oct 31 20:27:59 [rsHealthPoll] replSet info 10.250.7.220:27020 is down (or slow to respond): still initializing

Mon Oct 31 20:27:59 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state DOWN

Mon Oct 31 20:28:01 [initandlisten] connection accepted from 10.250.7.220:10857 #3

Mon Oct 31 20:28:05 [conn2] replSet RECOVERING

Mon Oct 31 20:28:05 [conn2] replSet info voting yea for 10.250.7.220:27018 (0)

Mon Oct 31 20:28:07 [rsHealthPoll] replSet member 10.250.7.220:27018 is now in state PRIMARY

Mon Oct 31 20:28:09 [FileAllocator] done allocating datafile /opt/mongodata/r2/local.2, size: 1024MB,  took 10.89 secs

Mon Oct 31 20:28:10 [rsSync] ******

Mon Oct 31 20:28:10 [rsSync] replSet initial sync pending

Mon Oct 31 20:28:10 [rsSync] replSet syncing to: 10.250.7.220:27018

Mon Oct 31 20:28:10 [rsSync] build index local.me { _id: 1 }

Mon Oct 31 20:28:10 [rsSync] build index done 0 records 0.001 secs

Mon Oct 31 20:28:10 [rsSync] replSet initial sync drop all databases

Mon Oct 31 20:28:10 [rsSync] dropAllDatabasesExceptLocal 1

Mon Oct 31 20:28:10 [rsSync] replSet initial sync clone all databases

Mon Oct 31 20:28:10 [rsSync] replSet initial sync query minValid

Mon Oct 31 20:28:10 [rsSync] replSet initial oplog application from 10.250.7.220:27018 starting at Oct 31 20:27:53:1 to Oct 31 20:27:53:1

Mon Oct 31 20:28:13 [rsHealthPoll] replSet info member 10.250.7.220:27020 is up

Mon Oct 31 20:28:13 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state STARTUP2

Mon Oct 31 20:28:14 [rsSync] replSet initial sync finishing up

Mon Oct 31 20:28:14 [rsSync] replSet set minValid=4eae9449:1

Mon Oct 31 20:28:14 [rsSync] build index local.replset.minvalid { _id: 1 }

Mon Oct 31 20:28:14 [rsSync] build index done 0 records 0.005 secs

Mon Oct 31 20:28:14 [rsSync] replSet initial sync done

Mon Oct 31 20:28:15 [rsSync] replSet syncing to: 10.250.7.220:27018

Mon Oct 31 20:28:15 [rsSync] replSet SECONDARY

Mon Oct 31 20:28:15 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state RECOVERING

Mon Oct 31 20:28:26 [clientcursormon] mem (MB) res:16 virt:2677 mapped:1232

Mon Oct 31 20:28:52 [initandlisten] connection accepted from 10.250.7.220:10872 #4

Mon Oct 31 20:28:52 [initandlisten] connection accepted from 10.250.7.220:10873 #5

Mon Oct 31 20:28:52 [rsGhostSync] handshake between 2 and 10.250.7.220:27018

Mon Oct 31 20:28:53 [slaveTracking] build index local.slaves { _id: 1 }

Mon Oct 31 20:28:53 [slaveTracking] build index done 0 records 0.003 secs

Mon Oct 31 20:28:55 [conn5] end connection 10.250.7.220:10873

Mon Oct 31 20:28:55 [conn4] end connection 10.250.7.220:10872

Mon Oct 31 20:28:57 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state SECONDARY

Mon Oct 31 20:29:27 [clientcursormon] mem (MB) res:19 virt:2693 mapped:1232

Mon Oct 31 20:30:21 [initandlisten] connection accepted from 127.0.0.1:44672 #6

Mon Oct 31 20:33:35 [conn2] end connection 10.250.7.220:42493

Mon Oct 31 20:33:35 [rsSync] replSet syncThread: 10278 dbclient error communicating with server: 10.250.7.220:27018

Mon Oct 31 20:33:35 [rsHealthPoll] DBClientCursor::init call() failed

Mon Oct 31 20:33:35 [rsHealthPoll] replSet info 10.250.7.220:27018 is down (or slow to respond): DBClientBase::findN: transport error: 10.250.7.220:27018 query: { replSetHeartbeat: "myset", v: 1, pv: 1, checkEmpty: false, from: "10.250.7.220:27019" }

Mon Oct 31 20:33:35 [rsHealthPoll] replSet member 10.250.7.220:27018 is now in state DOWN

Mon Oct 31 20:33:35 [rsMgr] not electing self, 10.250.7.220:27020 would veto

Mon Oct 31 20:33:36 [conn3] replSet info voting yea for 10.250.7.220:27020 (2)

Mon Oct 31 20:33:37 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state PRIMARY

Mon Oct 31 20:33:46 [rsSync] replSet syncing to: 10.250.7.220:27020

Mon Oct 31 20:34:27 [clientcursormon] mem (MB) res:19 virt:2693 mapped:1232

27020 端口的mongodb 输出日志显示的选择10.250.7.220 作为主库的日志记录

Mon Oct 31 20:33:35 [rsSync] replSet syncThread: 10278 dbclient error communicating with server: 10.250.7.220:27018

Mon Oct 31 20:33:36 [rsHealthPoll] DBClientCursor::init call() failed

Mon Oct 31 20:33:36 [rsHealthPoll] replSet info 10.250.7.220:27018 is down (or slow to respond): DBClientBase::findN: transport error: 10.250.7.220:27018 query: { replSetHeartbeat: "myset", v: 1, pv: 1, checkEmpty: false, from: "10.250.7.220:27020" }

Mon Oct 31 20:33:36 [rsHealthPoll] replSet member 10.250.7.220:27018 is now in state DOWN

Mon Oct 31 20:33:36 [rsMgr] replSet info electSelf 2

Mon Oct 31 20:33:36 [rsMgr] replSet PRIMARY

Mon Oct 31 20:33:46 [initandlisten] connection accepted from 10.250.7.220:37261 #5

Mon Oct 31 20:33:47 [slaveTracking] build index local.slaves { _id: 1 }

Mon Oct 31 20:33:47 [slaveTracking] build index done 0 records 0.001 secs

Mon Oct 31 20:33:48 [clientcursormon] mem (MB) res:19 virt:2692 mapped:1232

Mon Oct 31 20:34:35 [conn4] end connection 127.0.0.1:17500

Mon Oct 31 20:34:37 [initandlisten] connection accepted from 127.0.0.1:36525 #6

进入数据库查看：

[mongodb@rac4 bin]$ ./mongo 127.0.0.1:27020

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27020/test

PRIMARY> 

PRIMARY> 

PRIMARY> db.isMaster();

{

        "setName" : "myset",

        "ismaster" : true,--成为主库master

        "secondary" : false,

        "hosts" : [

                "10.250.7.220:27020",

                "10.250.7.220:27019",

                "10.250.7.220:27018"

        ],

        "primary" : "10.250.7.220:27020",

        "me" : "10.250.7.220:27020",

        "maxBsonObjectSize" : 16777216,

        "ok" : 1

}

PRIMARY> 

重新启动端口为27018的mongodb的数据库服务：从日志中可以看出其进行恢复的操作记录

[mongodb@rac4 bin]$ ./mongod --dbpath /opt/mongodata/r1 --port 27018  --rest --replSet myset &

[1] 16290

[mongodb@rac4 bin]$ Mon Oct 31 20:48:32 [initandlisten] MongoDB starting : pid=16290 port=27018 dbpath=/opt/mongodata/r1 64-bit host=rac4

Mon Oct 31 20:48:32 [initandlisten] db version v2.0.1, pdfile version 4.5

Mon Oct 31 20:48:32 [initandlisten] git version: 3a5cf0e2134a830d38d2d1aae7e88cac31bdd684

Mon Oct 31 20:48:32 [initandlisten] build info: Linux bs-linux64.10gen.cc 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20 17:48:28 EST 2009 x86_64 BOOST_LIB_VERSION=1_41

Mon Oct 31 20:48:32 [initandlisten] options: { dbpath: "/opt/mongodata/r1", port: 27018, replSet: "myset", rest: true }

Mon Oct 31 20:48:32 [initandlisten] journal dir=/opt/mongodata/r1/journal

Mon Oct 31 20:48:32 [initandlisten] recover begin

Mon Oct 31 20:48:32 [initandlisten] recover lsn: 231055

Mon Oct 31 20:48:32 [initandlisten] recover /opt/mongodata/r1/journal/j._0

Mon Oct 31 20:48:32 [initandlisten] recover skipping application of section seq:198962 < lsn:231055

Mon Oct 31 20:48:32 [initandlisten] recover cleaning up

Mon Oct 31 20:48:32 [initandlisten] removeJournalFiles

Mon Oct 31 20:48:32 [initandlisten] recover done

Mon Oct 31 20:48:32 [initandlisten] waiting for connections on port 27018

Mon Oct 31 20:48:32 [websvr] admin web console waiting for connections on port 28018

Mon Oct 31 20:48:32 [initandlisten] connection accepted from 127.0.0.1:11930 #1

Mon Oct 31 20:48:32 [rsStart] replSet STARTUP2

Mon Oct 31 20:48:32 [rsHealthPoll] replSet info member 10.250.7.220:27019 is up

Mon Oct 31 20:48:32 [rsHealthPoll] replSet member 10.250.7.220:27019 is now in state SECONDARY

Mon Oct 31 20:48:32 [rsHealthPoll] replSet info member 10.250.7.220:27020 is up

Mon Oct 31 20:48:32 [rsHealthPoll] replSet member 10.250.7.220:27020 is now in state PRIMARY

Mon Oct 31 20:48:32 [rsSync] replSet SECONDARY

Mon Oct 31 20:48:33 [initandlisten] connection accepted from 10.250.7.220:35971 #2

Mon Oct 31 20:48:34 [initandlisten] connection accepted from 10.250.7.220:35972 #3

Mon Oct 31 20:48:36 [rsSync] replSet syncing to: 10.250.7.220:27020

Mon Oct 31 20:48:36 [rsSync] build index local.me { _id: 1 }

Mon Oct 31 20:48:36 [rsSync] build index done 0 records 0 secs

[mongodb@rac4 bin]$ ./mongo 127.0.0.1:27018

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27018/test

SECONDARY> 

SECONDARY> db.isMaster();

{

        "setName" : "myset",

        "ismaster" : false,   --端口为 27018的数据库服务变为从库

        "secondary" : true,

        "hosts" : [

                "10.250.7.220:27018",

                "10.250.7.220:27020",

                "10.250.7.220:27019"

        ],

        "primary" : "10.250.7.220:27020",

        "me" : "10.250.7.220:27018",

        "maxBsonObjectSize" : 16777216,

        "ok" : 1

}

SECONDARY> 

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