mongodb的資料由monogd伺服器儲存，由mongos對寫入的資料根據片鍵進行路由，整個過程對客戶端完全透明。對chunk的移動是由“平衡器”來決定的，當然加入chunk分佈不均勻了，我們也可以手工來操作

db.runCommand( { moveChunk : "" ,

find : {查詢條件} ,

to : "" } )

註釋：

moveChunk：一個集合的全字要加上資料庫的名稱：比如test.yql

find：一個查詢語句，對於指定集合中的符合查詢的資料或者chunk，系統自動查出from 的shard

to：指向chunk的目的shard

只要目的shard和源sharad同意指定的chunk由目的shard接管，命令就返回。遷移chunk是一個比較複雜的過程，它包括兩個內部通訊協議：

1 複製資料，包括在複製過程中的變化的資料

2 確保所有參與遷移的組成部分：目的shard ，源shard ，config server都確定遷移已經完成！

比如我們要將 yql.momo中的id>82842的部分由shard0001遷移到shard0002：

mongos> db.printShardingStatus()

--- Sharding Status ---

sharding version: { "_id" : 1, "version" : 3 }

shards:

{ "_id" : "shard0000", "host" : "10.250.7.225:27018" }

{ "_id" : "shard0001", "host" : "10.250.7.249:27019" }

{ "_id" : "shard0002", "host" : "10.250.7.241:27020" }

databases:

{ "_id" : "admin", "partitioned" : false, "primary" : "config" }

{ "_id" : "test", "partitioned" : true, "primary" : "shard0000" }

test.momo chunks:

shard0001 3

shard0002 3

shard0000 6

{ "id" : { $minKey : 1 } } --&gt> { "id" : 0 } on : shard0001 { "t" : 2000, "i" : 0 }

{ "id" : 0 } --&gt> { "id" : 11595 } on : shard0002 { "t" : 3000, "i" : 0 }

{ "id" : 11595 } --&gt> { "id" : 23191 } on : shard0001 { "t" : 4000, "i" : 0 }

{ "id" : 23191 } --&gt> { "id" : 31929 } on : shard0002 { "t" : 5000, "i" : 0 }

{ "id" : 31929 } --&gt> { "id" : 42392 } on : shard0001 { "t" : 6000, "i" : 0 }

{ "id" : 42392 } --&gt> { "id" : 62952 } on : shard0002 { "t" : 7000, "i" : 0 }

{ "id" : 62952 } --&gt> { "id" : 82842 } on : shard0000 { "t" : 7000, "i" : 1 }

{ "id" : 82842 } --&gt> { "id" : 102100 } on : shard0000 { "t" : 1000, "i" : 11 }

{ "id" : 102100 } --&gt> { "id" : 120602 } on : shard0000 { "t" : 1000, "i" : 13 }

{ "id" : 120602 } --&gt> { "id" : 287873 } on : shard0000 { "t" : 2000, "i" : 2 }

{ "id" : 287873 } --&gt> { "id" : 305812 } on : shard0000 { "t" : 2000, "i" : 6 }

{ "id" : 305812 } --&gt> { "id" : { $maxKey : 1 } } on : shard0000 { "t" : 2000, "i" : 7 }

test.yql chunks:

shard0001 2

shard0000 1

shard0002 1

{ "_id" : { $minKey : 1 } } --&gt> { "_id" : ObjectId("4eb298b3adbd9673afee95e3") } on : shard0001 { "t" : 4000, "i" : 0 }

{ "_id" : ObjectId("4eb298b3adbd9673afee95e3") } --&gt> { "_id" : ObjectId("4eb2a64640643e5bb60072f7") } on : shard0000 { "t" : 4000, "i" : 1 }

{ "_id" : ObjectId("4eb2a64640643e5bb60072f7") } --&gt> { "_id" : ObjectId("4eb2a65340643e5bb600e084") } on : shard0002 { "t" : 3000, "i" : 1 }

{ "_id" : ObjectId("4eb2a65340643e5bb600e084") } --&gt> { "_id" : { $maxKey : 1 } } on : shard0001 { "t" : 3000, "i" : 0 }

{ "_id" : "mongos", "partitioned" : false, "primary" : "shard0000" }

執行遷移命令：

mongos> db.adminCommand({moveChunk : "test.momo", find : {id:{$gt:82842}}, to : "shard0002"});

{ "millis" : 1474, "ok" : 1 }

再次檢視：

mongos> db.printShardingStatus()

--- Sharding Status ---

sharding version: { "_id" : 1, "version" : 3 }

shards:

{ "_id" : "shard0000", "host" : "10.250.7.225:27018" }

{ "_id" : "shard0001", "host" : "10.250.7.249:27019" }

{ "_id" : "shard0002", "host" : "10.250.7.241:27020" }

databases:

{ "_id" : "admin", "partitioned" : false, "primary" : "config" }

{ "_id" : "test", "partitioned" : true, "primary" : "shard0000" }

test.momo chunks:

shard0001 4

shard0000 4

shard0002 4

{ "id" : { $minKey : 1 } } --&gt> { "id" : 0 } on : shard0001 { "t" : 2000, "i" : 0 }

{ "id" : 0 } --&gt> { "id" : 11595 } on : shard0000 { "t" : 11000, "i" : 0 }

{ "id" : 11595 } --&gt> { "id" : 23191 } on : shard0001 { "t" : 4000, "i" : 0 }

{ "id" : 23191 } --&gt> { "id" : 31929 } on : shard0002 { "t" : 11000, "i" : 1 }

{ "id" : 31929 } --&gt> { "id" : 42392 } on : shard0001 { "t" : 6000, "i" : 0 }

{ "id" : 42392 } --&gt> { "id" : 62952 } on : shard0002 { "t" : 7000, "i" : 0 }

{ "id" : 62952 } --&gt> { "id" : 82842 } on : shard0001 { "t" : 8000, "i" : 0 }

{ "id" : 82842 } --&gt> { "id" : 102100 } on : shard0002 { "t" : 9000, "i" : 0 }

{ "id" : 102100 } --&gt> { "id" : 120602 } on : shard0000 { "t" : 10000, "i" : 1 }

{ "id" : 120602 } --&gt> { "id" : 287873 } on : shard0000 { "t" : 2000, "i" : 2 }

{ "id" : 287873 } --&gt> { "id" : 305812 } on : shard0000 { "t" : 2000, "i" : 6 }

{ "id" : 305812 } --&gt> { "id" : { $maxKey : 1 } } on : shard0002 { "t" : 10000, "i" : 0 }

test.yql chunks:

shard0001 2

shard0000 1

shard0002 1

{ "_id" : { $minKey : 1 } } --&gt> { "_id" : ObjectId("4eb298b3adbd9673afee95e3") } on : shard0001 { "t" : 4000, "i" : 0 }

{ "_id" : ObjectId("4eb298b3adbd9673afee95e3") } --&gt> { "_id" : ObjectId("4eb2a64640643e5bb60072f7") } on : shard0000 { "t" : 4000, "i" : 1 }

{ "_id" : ObjectId("4eb2a64640643e5bb60072f7") } --&gt> { "_id" : ObjectId("4eb2a65340643e5bb600e084") } on : shard0002 { "t" : 3000, "i" : 1 }

{ "_id" : ObjectId("4eb2a65340643e5bb600e084") } --&gt> { "_id" : { $maxKey : 1 } } on : shard0001 { "t" : 3000, "i" : 0 }

{ "_id" : "mongos", "partitioned" : false, "primary" : "shard0000" }

mongos>

從結果看出:並非所有id>82842的資料所在的chunk都遷移到了shard0002上面，[82842,102100] 和[305812 ,+∞]遷移到了shard0002.這個有點不明白？？

日誌記錄：

##發命令

Sat Nov 5 16:15:35 [conn1] CMD: movechunk: { moveChunk: "test.momo", find: { id: { $gt: 82842.0 } }, to: "shard0002" }

##遷移資料

Sat Nov 5 16:15:35 [conn1] moving chunk ns: test.momo moving ( ns:test.momo at: shard0000:10.250.7.225:27018 lastmod: 2|7 min: { id: 305812 } max: { id: MaxKey }) shard0000:10.250.7.225:27018 -> shard0002:10.250.7.241:27020

Sat Nov 5 16:15:36 [Balancer] distributed lock 'balancer/rac4:27017:1320477786:1804289383' acquired, ts : 4eb4f0a818ed672581e262dd

Sat Nov 5 16:15:36 [Balancer] distributed lock 'balancer/rac4:27017:1320477786:1804289383' unlocked.

Sat Nov 5 16:15:37 [conn1] created new distributed lock for test.momo on rac1:28001,rac2:28002,rac3:28003 ( lock timeout : 900000, ping interval : 30000, process : 0 )

Sat Nov 5 16:15:37 [conn1] ChunkManager: time to load chunks for test.momo: 0ms sequenceNumber: 10 version: 10|1

Sat Nov 5 16:15:41 [Balancer] distributed lock 'balancer/rac4:27017:1320477786:1804289383' acquired, ts : 4eb4f0ad18ed672581e262de

Sat Nov 5 16:15:41 [Balancer] chose [shard0002] to [shard0000] { _id: "test.momo-id_0.0", lastmod: Timestamp 3000|0, ns: "test.momo", min: { id: 0.0 }, max: { id: 11595 }, shard: "shard0002" }

Sat Nov 5 16:15:41 [Balancer] moving chunk ns: test.momo moving ( ns:test.momo at: shard0002:10.250.7.241:27020 lastmod: 3|0 min: { id: 0.0 } max: { id: 11595 }) shard0002:10.250.7.241:27020 -> shard0000:10.250.7.225:27018

Sat Nov 5 16:15:43 [Balancer] created new distributed lock for test.momo on rac1:28001,rac2:28002,rac3:28003 ( lock timeout : 900000, ping interval : 30000, process : 0 )

Sat Nov 5 16:15:43 [Balancer] ChunkManager: time to load chunks for test.momo: 0ms sequenceNumber: 11 version: 11|1

【Mongodb】Sharding 手工遷移chunk

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