Remove Shards from a Sharded Cluster从分片集群中删除分片

Ensure the balancer is enabled确保平衡器已启用

To migrate data from a shard, the balancer process must be enabled. To check the balancer state, use the sh.getBalancerState() method:要从分片迁移数据，必须启用平衡器进程。要检查平衡器状态，请使用sh.getBalancerState()方法：

sh.getBalancerState()

If the operation returns true, the balancer is enabled.如果操作返回true，则启用平衡器。

If the operation returns false, see Enable the Balancer.如果操作返回false，请参阅启用平衡器。

Determine the name of the shard to remove确定要删除的分片的名称

To find the name of the shard, run the listShards command:要查找分片的名称，请运行listShards命令：

db.adminCommand( { listShards: 1 } )

The shards._id field contains the shard name.shards._id字段包含分片名称。

Migrate sharded collection data with the balancer使用平衡器迁移分片集合数据

Run the removeShard command for the shard you want to remove:对要删除的分片运行removeShard命令：

db.adminCommand( { removeShard: "<shardName>" } )

The removeShard operation returns:removeShard操作返回：

{
   "msg" : "draining started successfully",
   "state" : "started",
   "shard" : "<shardName>",
   "note" : "you need to call moveCollection for collectionsToMove and afterwards movePrimary for the dbsToMove",
   "dbsToMove" : [
      "db1",
      "db2"
   ],
   collectionsToMove: ["db1.collA"]
   "ok" : 1,
   "operationTime" : Timestamp(1575398919, 2),
   "$clusterTime" : {
      "clusterTime" : Timestamp(1575398919, 2),
      "signature" : {
         "hash" : BinData(0,"Oi68poWCFCA7b9kyhIcg+TzaGiA="),
         "keyId" : Long("6766255701040824328")
      }
   }

The shard enters the draining state and the balancer begins migrating chunks from the removed shard to other shards in the cluster. 分片进入draining（耗尽）状态，平衡器开始将块从已删除的分片迁移到集群中的其他分片。These migrations happens slowly to avoid severe impact on the overall cluster. Depending on your network capacity and the amount of data, this operation can take from a few minutes to several days to complete.这些迁移过程缓慢，以避免对整个集群造成严重影响。根据您的网络容量和数据量，此操作可能需要几分钟到几天的时间才能完成。

Move unsharded collections to another shard将未分片的集合移动到另一个分片

1. Determine what collections need to be moved确定需要移动哪些集合

   To list the unsharded collections on the shard, use the aggregation stage $listClusterCatalog:要列出分片上的未分片集合，请使用聚合阶段$listClusterCatalog：

   use admin
   
   db.aggregate([
         { $listClusterCatalog: { shards: true } },
         { $match: {
               $and: [
                   { sharded: false },
                   { shards: '<shard_to_remove>' },
                   { type: { $nin: ["timeseries","view"] } },
                   { ns: { $not: { $regex: "^enxcol_\..*(\.esc|\.ecc|\.ecoc|\.ecoc\.compact)$" }}},
                   { $or: [{ns: {$not: { $regex: "\.system\." }}}, {ns: {$regex: "\.system\.buckets\."}}]},
                   { db: { $ne: 'config' } },
                   { db: { $ne: 'admin' } }
               ]}},
         { $project: {
            _id: 0,
            ns: {
                $cond: [
                    "$options.timeseries",
                    {
                        $replaceAll: {
                            input: "$ns",
                            find: ".system.buckets",
                            replacement: ""
                        }
                    },
                    "$ns"
                ]
            }
      }}
   ])

2. Move the collections one by one逐一移动集合

   To move the collection, run sh.moveCollection():要移动集合，请运行sh.moveCollection()：

   sh.moveCollection( "<database>.<collection>", "<ID of recipient shard>" )

   Note

   moveCollection fails if you run the command on a namespace that is sharded. If you receive this error message, ignore it and return to step 1 for the next collection.如果在分片的命名空间上运行该命令，moveCollection将失败。如果您收到此错误消息，请忽略它并返回步骤1进行下一次集合。

3. Return to step 1 to check that there are no remaining unsharded collections on the draining shard.返回步骤1，检查排水分片上是否没有剩余的未分片集合。

Change primary shard更改主分片

Run the db.printShardingStatus() method:运行db.printShardingStatus()方法：

db.printShardingStatus()

In the databases section of the command output, check the database.primary field. If the primary field is the removed shard, you must move that database's primary to a different shard.在命令输出的databases部分，检查database.primary字段。如果primary字段是已删除的分片，则必须将该数据库的主字段移动到其他分片。

To change a database's primary shard, run the movePrimary command.要更改数据库的主分片，请运行movePrimary命令。

db.adminCommand(
   {
      movePrimary: <dbName>,
      to: <shardName>
   }
)

Check migration status检查迁移状态

To check the progress of the migration, run removeShard from the admin database again:要检查迁移的进度，请再次从admin数据库中运行removeShard：

db.adminCommand( { removeShard: "<shardName>" } )

In the output, the remaining field includes these fields:在输出中，remaining字段包括以下字段：

Continue checking the status of the removeShard command until the number of chunks remaining is 0.继续检查removeShard命令的状态，直到剩余块数为0。

db.adminCommand( { removeShard: "<shardName>" } )

Finalize shard removal完成分片删除

To finalize the shard removal process, re-run the removeShard command:要完成分片删除过程，请重新运行removeShard命令：

db.adminCommand( { removeShard: <shardName> } )

If the shard is removed, the command output resembles the following:如果删除分片，命令输出类似于以下内容：

{
   msg: 'removeshard completed successfully',
   state: 'completed',
   shard: '<shardName>',
   ok: 1,
   '$clusterTime': {
      clusterTime: Timestamp({ t: 1721941519, i: 7 }),
      signature: {
         hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
         keyId: Long('0')
      }
   },
   operationTime: Timestamp({ t: 1721941519, i: 7 })
}