Shulou(Shulou.com)06/01 Report--

Last year's notes, continue to send.

First, how to remove fragments

1. Confirm that balancer is enabled.

Mongos > sh.getBalancerState () true

2. Remove fragments

Note: execute the command under admin db.

Mongos > use adminswitched to db adminmongos > db.runCommand ({removeShard: "shard3"}) {"msg": "draining started successfully", "state": "started", "shard": "shard3", "ok": 1}

3. Check the status of migration

Same execution

Mongos > use adminswitched to db adminmongos > db.runCommand ({removeShard: "shard3"}) {"msg": "draining ongoing", "state": "ongoing", "remaining": {"chunks": NumberLong (3), "dbs": NumberLong (0)}, "ok": 1}

The chunks in remaining indicates how many blocks have not been migrated.

4. Remove unfragmented data

In a cluster, a database with unsharded collections stores those collections only on a single shard.

That shard becomes the primary shard for that database. (Different databases in a cluster can have different primary shards.)

WARNING

Do not perform this procedure until you have finished draining the shard.

1) To determine if the shard you are removing is the primary shard for any of the cluster's databases, issue one of the following methods:

Sh.status ()

Db.printShardingStatus ()

In the resulting document, the databases field lists each database and its primary shard.

For example, the following database field shows that the products database uses mongodb0 as the primary shard:

{"_ id": "products", "partitioned": true, "primary": "mongodb0"}

2) To move a database to another shard, use the movePrimary command. For example, to migrate all remaining unsharded data from mongodb0 to mongodb1

Issue the following command:

Use admin

Db.runCommand ({movePrimary: "products", to: "mongodb1"})-products is db name

This command does not return until MongoDB completes moving all data, which may take a long time.

The response from this command will resemble the following:

{"primary": "mongodb1", "ok": 1}

If you use the movePrimary command to move un-sharded collections, you must either restart all mongos instances

Or use the flushRouterConfig command on all mongos instances before writing any data to the cluster.

This action notifies the mongos of the new shard for the database.

If you do not update the mongos instances' metadata cache after using movePrimary, the mongos may not write data to the correct shard.

To recover, you must manually intervene.

According to the above, it is best to stop when migrating non-sharded tables, after running the db.runCommand ({movePrimary: "products", to: "mongodb1"}) command is complete.

Refresh all mongos (running db.runCommand ("flushRouterConfig") on all mongos) before providing services to the outside world. Of course, you can restart all mongos instances.

5. Complete the migration

Mongos > use adminswitched to db adminmongos > db.runCommand ({removeShard: "shard3"}) {"msg": "removeshard completed successfully", "state": "completed", "shard": "shard3", "ok": 1}

If state is completed, the migration is complete.

Add slicing

1. First make sure that balancer is enabled.

Mongos > sh.getBalancerState () true

2. Execute the command to add shards.

If the following error occurs, delete the test1 database on the target shard3 and execute the command again

Mongos > sh.addShard ("shard3/192.168.137.138:27019") {"ok": 0, "errmsg": "can't add shard shard3/192.168.137.138:27019 because a local database 'test1' exists in another shard1:shard1/192.168.137.111:27017192.168.137.75:27017"} mongos > sh.addShard ("shard3/192.168.137.138:27019") {"shardAdded": "shard3", "ok": 1}

Finally, it may take a long time to run the sh.status () command to confirm that the migration was successful.

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