MongoDB Sharding Learning Operation part 2

Take on the last article

14. Configure the balancer process in the cluster

The balancer process runs on one of the mongos instances in the cluster, ensuring that the chunks is evenly distributed across the cluster.

Change the maximum storage size of the specified shard

15. Remove a shard from an existing sharding cluster

Before removing a shard, you need to make sure that the data on that shard has been moved to another shard.

1) make sure that the Blancer process is enabled

Sh.getBalancerState ()

2) determine the name of the shard to be removed

Db.adminCommand ({listShards: 1})

Or

Db.printShardingStatus ()

Or

Sh.status ()

3) remove data blocks from the shard

Mongos > use admin;switched to db adminmongos > db.runCommand ({removeShard: "taiwan_shard1"}) {"msg": "draining started successfully", "state": "started", "shard": "taiwan_shard1", "ok": 1}

Depending on the state of the network and the amount of data, this operation may take several minutes or days to complete.

4) check the status of the migration

Mongos > db.runCommand ({removeShard: "taiwan_shard1"}) {"msg": "draining ongoing", "state": "ongoing", "remaining": {"chunks": NumberLong (0), "dbs": NumberLong (2)}, "note": "you need to drop or movePrimary these databases" "dbsToMove": ["taiwan_game4", "taiwan_game5"], "ok": 1}

It is important to note that if a shard is the primary shard of one or more databases, then the shard contains unshredded data.

Mongos > use admin Switched to db adminmongos > db.runCommand ({movePrimary: "taiwan_game4", to: "taiwan_shard2"}) {"primary": "taiwan_shard2:taiwan_shard2/gintama-taiwan-mongodb2:28018", "ok": 1} mongos > db.runCommand ({movePrimary: "taiwan_game5", to: "taiwan_shard2"}) {"primary": "taiwan_shard2:taiwan_shard2/gintama-taiwan-mongodb2:28018" "ok": 1}

5) end the migration process

Mongos > db.runCommand ({removeShard: "taiwan_shard1"}) {"msg": "removeshard completed successfully", "state": "completed", "shard": "taiwan_shard1", "ok": 1}

When the state status is completed, the migration is complete.

Reference documentation:

Http://docs.mongodb.org/v2.4/tutorial/remove-shards-from-cluster/