Scale in and out

This topic describes how to scale in and out the node of StarRocks.

Scale FE in and out

StarRocks has two types of FE nodes: Follower and Observer. Followers are involved in election voting and writing. Observers are only used to synchronize logs and extend read performance.

• The number of follower FEs (including leader) must be odd, and it is recommended to deploy 3 of them to form a High Availability (HA) mode.
• When the FE is in high availability deployment (1 leader, 2 followers), it is recommended to add Observer FEs for better read performance. * Typically one FE node can work with 10-20 BE nodes. It is recommended that the total number of FE nodes be less than 10. Three is sufficient in most cases.

Scale FE out

After deploying the FE node and starting the service, run the following command to scale FE out.

alter system add follower "fe_host:edit_log_port";
alter system add observer "fe_host:edit_log_port";

Scale FE in

FE scale-in is similar to the scale-out. Run the following command to scale FE in.

alter system drop follower "fe_host:edit_log_port";
alter system drop observer "fe_host:edit_log_port";

After the expansion and contraction, you can view the node information by running show proc '/frontends';.

Scale BE in and out

After BE is scaled in or out, StarRocks will automatically perform load-balancing without affecting the overall performance.

Scale BE out

Run the following command to scale BE out.

alter system add backend 'be_host:be_heartbeat_service_port';

Run the following command to check the BE status.

show proc '/backends';

Scale BE in

There are two ways to scale in a BE node – DROP and DECOMMISSION.

DROP will delete the BE node immediately, and the lost duplicates will be made up by FE scheduling. DECOMMISSION will make sure the duplicates are made up first, and then drop the BE node. DECOMMISSION is a bit more friendly and is recommended for BE scale-in.

The commands of both methods are similar:

• alter system decommission backend "be_host:be_heartbeat_service_port";
• alter system drop backend "be_host:be_heartbeat_service_port";

Drop backend is a dangerous operation, so you need to confirm it twice before executing it

• alter system drop backend "be_host:be_heartbeat_service_port";

After the scale-out or scale-in, you can check the status of FE and BE by referring to Cluster Status.