在分片群集中合并块
在本页面
Overview
在版本 3.0 中更改。
mergeChunks命令允许您将同一分片上的连续块合并为一个块。本教程说明了如何合并分片群集中的相邻块。
Procedure
Note
此过程中的示例在test database中使用members collection，并将username字段用作shard key。
识别块范围
在mongo shell 中，通过以下操作确定chunk范围：
sh.status()
在输出中，块范围出现在每个分片集合的块计数之后，如以下示例所示：
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5c0e886b6602192935f35008")
}
shards:
{ "_id" : "shardA", "host" : "shardA/shardA-m1.example.net:27018,shardA-m2.example.net:27018,shardA-m3.example.net:27018", "state" : 1 }
{ "_id" : "shardB", "host" : "shardB/shardB-m1.example.net:27018,shardB-m2.example.net:27018,shardB-m3.example.net:27018", "state" : 1 }
active mongoses:
"3.6.8" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
7 : Success
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shardA 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 0)
{ "_id" : "test", "primary" : "shardA", "partitioned" : true }
test.members
shard key: { "username" : 1 }
unique: false
balancing: true
chunks:
shardA 7
shardB 7
{ "username" : { "$minKey" : 1 } } -->> { "username" : "user16643" } on : shardB Timestamp(2, 0)
{ "username" : "user16643" } -->> { "username" : "user2329" } on : shardB Timestamp(3, 0)
{ "username" : "user2329" } -->> { "username" : "user29937" } on : shardB Timestamp(4, 0)
{ "username" : "user29937" } -->> { "username" : "user36583" } on : shardB Timestamp(5, 0)
{ "username" : "user36583" } -->> { "username" : "user43229" } on : shardB Timestamp(6, 0)
{ "username" : "user43229" } -->> { "username" : "user49877" } on : shardB Timestamp(7, 0)
{ "username" : "user49877" } -->> { "username" : "user56522" } on : shardB Timestamp(8, 0)
{ "username" : "user56522" } -->> { "username" : "user63169" } on : shardA Timestamp(8, 1)
{ "username" : "user63169" } -->> { "username" : "user69816" } on : shardA Timestamp(1, 17)
{ "username" : "user69816" } -->> { "username" : "user76462" } on : shardA Timestamp(1, 19)
{ "username" : "user76462" } -->> { "username" : "user83108" } on : shardA Timestamp(1, 21)
{ "username" : "user83108" } -->> { "username" : "user89756" } on : shardA Timestamp(1, 23)
{ "username" : "user89756" } -->> { "username" : "user96401" } on : shardA Timestamp(1, 25)
{ "username" : "user96401" } -->> { "username" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 26)
在每个分片集合的块计数之后，将出现块范围。例如，以下是test.members集合的块范围：
{ "username" : { "$minKey" : 1 } } -->> { "username" : "user16643" } on : shardB Timestamp(2, 0)
{ "username" : "user16643" } -->> { "username" : "user2329" } on : shardB Timestamp(3, 0)
{ "username" : "user2329" } -->> { "username" : "user29937" } on : shardB Timestamp(4, 0)
{ "username" : "user29937" } -->> { "username" : "user36583" } on : shardB Timestamp(5, 0)
{ "username" : "user36583" } -->> { "username" : "user43229" } on : shardB Timestamp(6, 0)
{ "username" : "user43229" } -->> { "username" : "user49877" } on : shardB Timestamp(7, 0)
{ "username" : "user49877" } -->> { "username" : "user56522" } on : shardB Timestamp(8, 0)
{ "username" : "user56522" } -->> { "username" : "user63169" } on : shardA Timestamp(8, 1)
{ "username" : "user63169" } -->> { "username" : "user69816" } on : shardA Timestamp(1, 17)
{ "username" : "user69816" } -->> { "username" : "user76462" } on : shardA Timestamp(1, 19)
{ "username" : "user76462" } -->> { "username" : "user83108" } on : shardA Timestamp(1, 21)
{ "username" : "user83108" } -->> { "username" : "user89756" } on : shardA Timestamp(1, 23)
{ "username" : "user89756" } -->> { "username" : "user96401" } on : shardA Timestamp(1, 25)
{ "username" : "user96401" } -->> { "username" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 26)
Merge Chunks
将连续的chunks合并到同一分片上。
例如，考虑shardA上的以下块范围：
Note
要合并的块突出显示。
{ "username" : "user56522" } -->> { "username" : "user63169" } on : shardA Timestamp(8, 1)
{ "username" : "user63169" } -->> { "username" : "user69816" } on : shardA Timestamp(1, 17)
{ "username" : "user69816" } -->> { "username" : "user76462" } on : shardA Timestamp(1, 19)
{ "username" : "user76462" } -->> { "username" : "user83108" } on : shardA Timestamp(1, 21)
{ "username" : "user83108" } -->> { "username" : "user89756" } on : shardA Timestamp(1, 23)
{ "username" : "user89756" } -->> { "username" : "user96401" } on : shardA Timestamp(1, 25)
{ "username" : "user96401" } -->> { "username" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 26)
要合并突出显示的连续块，请对admin数据库发出mergeChunks命令：
db.adminCommand( {
mergeChunks: "test.members",
bounds: [ { "username" : "user69816" },
{ "username" : "user96401" } ]
} )
成功后，mergeChunks产生以下输出：
{
"ok" : 1,
"operationTime" : Timestamp(1544636362, 12),
"$clusterTime" : {
"clusterTime" : Timestamp(1544636362, 13),
"signature" : {
"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
"keyId" : NumberLong(0)
}
}
}
在任何失败情况下，mergeChunks都会返回一个文档，其中ok字段的值为0。
查看合并的块范围
合并标识的块之后，请确认新的块，如下所示：
sh.status()
sh.status()的输出应类似于：
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("5c0e886b6602192935f35008")
}
shards:
{ "_id" : "shardA", "host" : "shardA/shardA-m1.example.net:27018,shardA-m2.example.net:27018,shardA-m3.example.net:27018", "state" : 1 }
{ "_id" : "shardB", "host" : "shardB/shardB-m1.example.net:27018,shardB-m2.example.net:27018,shardB-m3.example.net:27018", "state" : 1 }
active mongoses:
"3.6.8" : 1
autosplit:
Currently enabled: yes
balancer:
Currently enabled: yes
Currently running: no
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
8 : Success
databases:
{ "_id" : "config", "primary" : "config", "partitioned" : true }
config.system.sessions
shard key: { "_id" : 1 }
unique: false
balancing: true
chunks:
shardA 1
{ "_id" : { "$minKey" : 1 } } -->> { "_id" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 0)
{ "_id" : "test", "primary" : "shardA", "partitioned" : true }
test.members
shard key: { "username" : 1 }
unique: false
balancing: true
chunks:
shardA 5
shardB 6
{ "username" : { "$minKey" : 1 } } -->> { "username" : "user16643" } on : shardA Timestamp(9, 0)
{ "username" : "user16643" } -->> { "username" : "user2329" } on : shardB Timestamp(9, 1)
{ "username" : "user2329" } -->> { "username" : "user29937" } on : shardB Timestamp(4, 0)
{ "username" : "user29937" } -->> { "username" : "user36583" } on : shardB Timestamp(5, 0)
{ "username" : "user36583" } -->> { "username" : "user43229" } on : shardB Timestamp(6, 0)
{ "username" : "user43229" } -->> { "username" : "user49877" } on : shardB Timestamp(7, 0)
{ "username" : "user49877" } -->> { "username" : "user56522" } on : shardB Timestamp(8, 0)
{ "username" : "user56522" } -->> { "username" : "user63169" } on : shardA Timestamp(8, 1)
{ "username" : "user63169" } -->> { "username" : "user69816" } on : shardA Timestamp(1, 17)
{ "username" : "user69816" } -->> { "username" : "user96401" } on : shardA Timestamp(8, 2)
{ "username" : "user96401" } -->> { "username" : { "$maxKey" : 1 } } on : shardA Timestamp(1, 26)
合并之后，balancer可以跨碎片迁移块，以确保块的分布更加均匀。