Mongodb延迟复制节点配置

背景：

我们一般配置的Mongodb主从，或者Mongodb复制集，数据同步都是实时的。但如果在主节点上进行了错误的数据操作，这时候就会导致整个集群的数据都出错。因此，我们可以在一个集群中，挑选一个mongodb实例，用作复制延迟。当在主节点上误操作的时候，集群中有一个实例是不受影响的。这时候就可以利用这台不受影响的实例进行数据恢复。

以上就是mongodb的延迟复制节点的功能，当主节点进行一次数据操作后，延迟复制节不立马进行数据同步操作，而是在一段时间后，才同步数据。

配置：

以我的实验环境为例，以下为我的mongodb复制集：

cmh0:PRIMARY> rs.status(){        "set" : "cmh0",        "date" : ISODate("2016-08-22T02:43:16.240Z"),        "myState" : 1,        "members" : [                {                        "_id" : 1,                        "name" : "192.168.52.128:27017",                        "health" : 1,                        "state" : 1,                        "stateStr" : "PRIMARY",                        "uptime" : 82,                        "optime" : Timestamp(1470581983, 1),                        "optimeDate" : ISODate("2016-08-07T14:59:43Z"),                        "electionTime" : Timestamp(1471833721, 1),                        "electionDate" : ISODate("2016-08-22T02:42:01Z"),                        "configVersion" : 1,                        "self" : true                },                {                        "_id" : 2,                        "name" : "192.168.52.135:27017",                        "health" : 1,                        "state" : 2,                        "stateStr" : "SECONDARY",                        "uptime" : 71,                        "optime" : Timestamp(1470581983, 1),                        "optimeDate" : ISODate("2016-08-07T14:59:43Z"),                        "lastHeartbeat" : ISODate("2016-08-22T02:43:15.138Z"),                        "lastHeartbeatRecv" : ISODate("2016-08-22T02:43:14.978Z"),                        "pingMs" : 0,                        "lastHeartbeatMessage" : "could not find member to sync from",                        "configVersion" : 1                },                {                        "_id" : 3,                        "name" : "192.168.52.135:27019",                        "health" : 1,                        "state" : 2,                        "stateStr" : "SECONDARY",                        "uptime" : 75,                        "optime" : Timestamp(1470581983, 1),                        "optimeDate" : ISODate("2016-08-07T14:59:43Z"),                        "lastHeartbeat" : ISODate("2016-08-22T02:43:15.138Z"),                        "lastHeartbeatRecv" : ISODate("2016-08-22T02:43:15.138Z"),                        "pingMs" : 0,                        "configVersion" : 1                }        ],        "ok" : 1}

这时还未配置延迟复制节点，所以数据是实时同步的：

cmh0:PRIMARY> use cmhtestswitched to db cmhtestcmh0:PRIMARY> db.cmh.insert({"name":"ChenMinghui"})WriteResult({ "nInserted" : 1 })cmh0:PRIMARY> rs.printReplicationInfo()configured oplog size:   990MBlog length start to end: 195secs (0.05hrs)oplog first event time:  Mon Aug 22 2016 10:51:22 GMT+0800 (CST)oplog last event time:   Mon Aug 22 2016 10:54:37 GMT+0800 (CST)now:                     Mon Aug 22 2016 10:55:00 GMT+0800 (CST)cmh0:PRIMARY> rs.printSlaveReplicationInfo()source: 192.168.52.135:27017        syncedTo: Mon Aug 22 2016 10:54:37 GMT+0800 (CST)        0 secs (0 hrs) behind the primary source: 192.168.52.135:27019        syncedTo: Mon Aug 22 2016 10:54:37 GMT+0800 (CST)        0 secs (0 hrs) behind the primary

可以看到两个Secondary节点都在同一时间实时同步了数据。

配置192.168.52.135:27017为延迟复制节点：

cmh0:PRIMARY> cfg=rs.conf();{        "_id" : "cmh0",        "version" : 1,        "members" : [                {                        "_id" : 1,                        "host" : "192.168.52.128:27017",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 1,                        "tags" : {                        },                        "slaveDelay" : 0,                        "votes" : 1                },                {                        "_id" : 2,                        "host" : "192.168.52.135:27017",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 1,                        "tags" : {                        },                        "slaveDelay" : 0,                        "votes" : 1                },                {                        "_id" : 3,                        "host" : "192.168.52.135:27019",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 1,                        "tags" : {                        },                        "slaveDelay" : 0,                        "votes" : 1                }        ],        "settings" : {                "chainingAllowed" : true,                "heartbeatTimeoutSecs" : 10,                "getLastErrorModes" : {                },                "getLastErrorDefaults" : {                        "w" : 1,                        "wtimeout" : 0                }        }}cmh0:PRIMARY> cfg.members[1].priority=00cmh0:PRIMARY> cfg.members[1].slaveDelay=3030cmh0:PRIMARY> rs.reconfig(cfg);{ "ok" : 1 }cmh0:PRIMARY> rs.conf(){        "_id" : "cmh0",        "version" : 2,        "members" : [                {                        "_id" : 1,                        "host" : "192.168.52.128:27017",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 1,                        "tags" : {                        },                        "slaveDelay" : 0,                        "votes" : 1                },                {                        "_id" : 2,                        "host" : "192.168.52.135:27017",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 0,                        "tags" : {                        },                        "slaveDelay" : 30,                        "votes" : 1                },                {                        "_id" : 3,                        "host" : "192.168.52.135:27019",                        "arbiterOnly" : false,                        "buildIndexes" : true,                        "hidden" : false,                        "priority" : 1,                        "tags" : {                        },                        "slaveDelay" : 0,                        "votes" : 1                }        ],        "settings" : {                "chainingAllowed" : true,                "heartbeatTimeoutSecs" : 10,                "getLastErrorModes" : {                },                "getLastErrorDefaults" : {                        "w" : 1,                        "wtimeout" : 0                }        }}

可以看到192.168.52.135:27017节点出现了"slaveDelay":30的值，说明该节点的同步时间向后推迟了30秒。

具体大家可以测试一下，延迟复制时间大概会在30秒左右。有一点要注意，mongodb的系统时间必须一致，否则会造成延迟复制异常，导致在规定同步时间到了之后不进行同步操作。