對於Replica Set中的選擇策略：

We use a consensus protocol to pick a primary. Exact details will be spared here but that basic process is:

1 get maxLocalOpOrdinal from each server.

2 if a majority of servers are not up (from this server's POV), remain in Secondary mode and stop.

3 if the last op time seems very old, stop and await human intervention.

4 else, using a consensus protocol, pick the server with the highest maxLocalOpOrdinal as the Primary.

對於策略2：當叢集裡的大多數伺服器發生down 機了,剩餘的節點就會保持在secondary模式並停止服務。

做了實驗結果是對於4節點的 Replica Set，當兩個secondary節點down了的時候，主節點變為secondary。整個叢集相當於掛了，因為secondary 不提供讀寫操作。。

在一個叢集中關閉兩個secondary 節點：rac4:27019和rac3:27017

[mongodb@rac4 bin]$ ./mongo 127.0.0.1:27019

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27019/test

SECONDARY>

SECONDARY> use admin

switched to db admin

SECONDARY> db.shutdownServer();

Wed Nov 2 11:02:29 DBClientCursor::init call() failed

Wed Nov 2 11:02:29 query failed : admin.$cmd { shutdown: 1.0 } to: 127.0.0.1:27019

server should be down...

[mongodb@rac3 bin]$ ./mongo 10.250.7.241:27017

MongoDB shell version: 2.0.1

connecting to: 127.0.0.1:27017/test

SECONDARY>

SECONDARY> use admin

switched to db admin

SECONDARY> db.shutdownServer();

Tue Nov 1 22:02:46 DBClientCursor::init call() failed

Tue Nov 1 22:02:46 query failed : admin.$cmd { shutdown: 1.0 } to: 127.0.0.1:27017

server should be down...

Tue Nov 1 22:02:46 trying reconnect to 127.0.0.1:27017

Tue Nov 1 22:02:46 reconnect 127.0.0.1:27017 failed couldn't connect to server 127.0.0.1:27017

Tue Nov 1 22:02:46 Error: error doing query: unknown shell/collection.js:150

從主庫的客戶端退出以後，再次進入提示符發生變化：由PRIMARY---&gtSECONDARY ，檢視Replica Set的狀態資訊：

[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> rs.status();

{

"set" : "myset",

"date" : ISODate("2011-11-01T13:56:05Z"),

"myState" : 2,

"members" : [

{

"_id" : 0,

"name" : "10.250.7.220:27018",

"health" : 1,

"state" : 2,

"stateStr" : "SECONDARY",

"uptime" : 101,

"optime" : {

"t" : 1320154033000,

"i" : 1

},

"optimeDate" : ISODate("2011-11-01T13:27:13Z"),

"lastHeartbeat" : ISODate("2011-11-01T13:56:04Z"),

"pingMs" : 0

},

{

"_id" : 1,

"name" : "10.250.7.220:27019",

"health" : 0, --已經關閉

"state" : 8,

"stateStr" : "(not reachable/healthy)",

"uptime" : 0,

"optime" : {

"t" : 1320154033000,

"i" : 1

},

"optimeDate" : ISODate("2011-11-01T13:27:13Z"),

"lastHeartbeat" : ISODate("2011-11-01T13:53:50Z"),

"pingMs" : 0,

"errmsg" : "socket exception"

},

{

"_id" : 2,

"name" : "10.250.7.220:27020",

"health" : 1,

"state" : 2,

"stateStr" : "SECONDARY", ---由主庫變為從庫

"optime" : {

"t" : 1320154033000,

"i" : 1

},

"optimeDate" : ISODate("2011-11-01T13:27:13Z"),

"self" : true

},

{

"_id" : 3,

"name" : "10.250.7.241:27017",

"health" : 0,

"state" : 8,

"stateStr" : "(not reachable/healthy)",

"uptime" : 0,

"optime" : {

"t" : 1320154033000,

"i" : 1

},

"optimeDate" : ISODate("2011-11-01T13:27:13Z"),

"lastHeartbeat" : ISODate("2011-11-01T13:53:54Z"),

"pingMs" : 0,

"errmsg" : "socket exception"

}

],

"ok" : 1

}

SECONDARY> exut

Wed Nov 2 15:23:02 ReferenceError: exut is not defined (shell):1

Wed Nov 2 15:23:02 DBClientCursor::init call() failed

> exit

bye

未完待續。。。。

【Mongodb】 Replica set 的選舉策略之二

相關文章

【Mongodb】 Replica set 的 選舉策略之二

相關文章

【Mongodb】 Replica set 的選舉策略之二