我们有一个 mongoDb 集群，有 3 个 shard，每个 shard 是一个包含 3 个节点的副本集，我们使用的 mongoDb 版本是 3.2.6。我们有一个大小约为 230G 的大型数据库，其中包含大约 5500 个集合。我们发现大约 2300 个集合不平衡，而其他 3200 个集合均匀分布到 3 个分片。
下面是 sh.status 的结果（整个结果太大了，我只贴一部分）：
mongos> sh.status()
--- Sharding Status ---
sharding version: {
"_id" : 1,
"minCompatibleVersion" : 5,
"currentVersion" : 6,
"clusterId" : ObjectId("57557345fa5a196a00b7c77a")
}
shards:
{ "_id" : "shard1", "host" : "shard1/10.25.8.151:27018,10.25.8.159:27018" }
{ "_id" : "shard2", "host" : "shard2/10.25.2.6:27018,10.25.8.178:27018" }
{ "_id" : "shard3", "host" : "shard3/10.25.2.19:27018,10.47.102.176:27018" }
active mongoses:
"3.2.6" : 1
balancer:
Currently enabled: yes
Currently running: yes
Balancer lock taken at Sat Sep 03 2016 09:58:58 GMT+0800 (CST) by iZ23vbzyrjiZ:27017:1467949335:-2109714153:Balancer
Collections with active migrations:
bdtt.normal_20131017 started at Sun Sep 18 2016 17:03:11 GMT+0800 (CST)
Failed balancer rounds in last 5 attempts: 0
Migration Results for the last 24 hours:
1490 : Failed with error 'aborted', from shard2 to shard3
1490 : Failed with error 'aborted', from shard2 to shard1
14 : Failed with error 'data transfer error', from shard2 to shard1
databases:
{ "_id" : "bdtt", "primary" : "shard2", "partitioned" : true }
bdtt.normal_20160908
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard2 142
too many chunks to print, use verbose if you want to force print
bdtt.normal_20160909
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard1 36
shard2 42
shard3 46
too many chunks to print, use verbose if you want to force print
bdtt.normal_20160910
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard1 34
shard2 32
shard3 32
too many chunks to print, use verbose if you want to force print
bdtt.normal_20160911
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard1 30
shard2 32
shard3 32
too many chunks to print, use verbose if you want to force print
bdtt.normal_20160912
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard2 126
too many chunks to print, use verbose if you want to force print
bdtt.normal_20160913
shard key: { "_id" : "hashed" }
unique: false
balancing: true
chunks:
shard2 118
too many chunks to print, use verbose if you want to force print
}
集合“normal_20160913”不平衡，我在下面发布了这个集合的 getShardDistribution() 结果：
mongos> db.normal_20160913.getShardDistribution()
Shard shard2 at shard2/10.25.2.6:27018,10.25.8.178:27018
data : 4.77GiB docs : 203776 chunks : 118
estimated data per chunk : 41.43MiB
estimated docs per chunk : 1726
Totals
data : 4.77GiB docs : 203776 chunks : 118
Shard shard2 contains 100% data, 100% docs in cluster, avg obj size on shard : 24KiB
balancer 进程处于运行状态，chunksize 为默认（64M）：
mongos> sh.isBalancerRunning()
true
mongos> use config
switched to db config
mongos> db.settings.find()
{ "_id" : "chunksize", "value" : NumberLong(64) }
{ "_id" : "balancer", "stopped" : false }
而且我从mogos日志中发现了很多moveChunk错误，这可能是一些集合不平衡的原因，这里是它们的最新部分：
2016-09-19T14:25:25.427+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:25:59.620+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:25:59.644+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:35:02.701+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:35:02.728+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:42:18.232+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:42:18.256+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:42:27.101+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:42:27.112+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
2016-09-19T14:43:41.889+0800 I SHARDING [conn37136926] moveChunk result: { ok: 0.0, errmsg: "Not starting chunk migration because another migration is already in progress", code: 117 }
我尝试手动使用 moveChunk 命令，它返回相同的错误：
mongos> sh.moveChunk("bdtt.normal_20160913", {_id:ObjectId("57d6d107edac9244b6048e65")}, "shard3")
{
"cause" : {
"ok" : 0,
"errmsg" : "Not starting chunk migration because another migration is already in progress",
"code" : 117
},
"code" : 117,
"ok" : 0,
"errmsg" : "move failed"
}
我不确定是否创建了太多导致迁移不堪重负的集合？每天将创建大约 60-80 个新集合。
我需要帮助来回答以下问题，任何提示都会很棒：
- 为什么有些收藏不平衡，是不是跟新创建的收藏多有关？
- 是否有任何命令可以检查处理迁移作业的详细信息？我得到了很多错误日志，显示一些迁移慢跑正在运行，但我找不到正在运行的。