Region Migration

Region Migration allows users to move regions between the Datanode.

Warning

This feature is only available on GreptimeDB running on distributed mode and

• Using Kafka WAL
• Using shared storage (e.g., AWS S3)

Otherwise, you can't perform a region migration.

Figure out the region distribution of the table.

You need to first query the region distribution of the table, i.e., find out on which Datanode the Regions in the table are located.

select b.peer_id as datanode_id,
       a.greptime_partition_id as region_id
from information_schema.partitions a left join information_schema.region_peers b
on a.greptime_partition_id = b.region_id where a.table_name='migration_target' order by datanode_id asc;

For example, have the following region distribution:

+-------------+---------------+
| datanode_id | region_id     |
+-------------+---------------+
|           1 | 4398046511104 |
+-------------+---------------+
1 row in set (0.01 sec)

For more info about the region_peers table, please read the REGION-PEERS.

Select a Datanode as the migration destination.

Warning

The region migration won't be performed if the from_peer_id equals the to_peer_id.

Remember, if you deploy the cluster via the GreptimeDB operator, the peer_id of Datanode always starts from 0. For example, if you have a 3 Datanode GreptimeDB cluster, the available peer_id will be 0,1,2.

Finally, you can do a Region migration request via the following SQL:

select migrate_region(4398046511104, 1, 2, 60);

The parameters of migrate_region：

select migrate_region(region_id, from_peer_id, to_peer_id, replay_timeout);

Option	Description	Required
region_id	The region id.	Required
from_peer_id	The peer id of the migration source(Datanode).	Required
to_peer_id	The peer id of the migration destination(Datanode).	Required
replay_timeout	The timeout(secs) of replay data. If the new Region fails to replay the data within the specified timeout, the migration will fail, however the data in the old Region will not be lost.	Optional

Query the migration state

The migrate_region function returns the procedure id that executes the migration, queries the procedure state by it:

select procedure_state('538b7476-9f79-4e50-aa9c-b1de90710839')

If it's done, outputs the state in JSON:

 {"status":"Done"}

Of course, you can confirm the region distribution by querying from region_peers and partitions in information_schema.