START_DRAIN_SUBCLUSTER

Drains a subcluster or subclusters.

Eon Mode only

Drains a subcluster or subclusters. The function marks all nodes in the designated subcluster as draining. Work from existing user sessions continues on draining nodes, but the nodes refuse new client connections and are excluded from load balancing operations. dbadmin can still connect to draining nodes.

To drain connections on a subcluster as part of a graceful shutdown process, you can call SHUTDOWN_WITH_DRAIN. For details, see Graceful Shutdown.

To cancel a draining operation on a subcluster, call CANCEL_DRAIN_SUBCLUSTER. If all draining nodes in a subcluster are stopped, they are marked as not draining upon restart.

This is a meta-function. You must call meta-functions in a top-level SELECT statement.

Behavior type

Volatile

Syntax

START_DRAIN_SUBCLUSTER( 'subcluster-name' )

Arguments

subcluster-name: Name of the subcluster to drain. Enter an empty string to drain all subclusters in the database.

Privileges

Superuser

Examples

The following example demonstrates how to drain a subcluster named analytics:

=> SELECT subcluster_name, node_name, node_state FROM nodes;
subcluster_name    |      node_name     | node_state
-------------------+--------------------+------------
default_subcluster | verticadb_node0001 | UP
default_subcluster | verticadb_node0002 | UP
default_subcluster | verticadb_node0003 | UP
analytics          | verticadb_node0004 | UP
analytics          | verticadb_node0005 | UP
analytics          | verticadb_node0006 | UP
(6 rows)

=> SELECT START_DRAIN_SUBCLUSTER('analytics');
               START_DRAIN_SUBCLUSTER
-------------------------------------------------------
Targeted subcluster: 'analytics'
Action: START DRAIN
(1 row)

You can confirm that the subcluster is draining by querying the DRAINING_STATUS system table:


=> SELECT node_name, subcluster_name, is_draining FROM draining_status ORDER BY 1;
node_name          | subcluster_name    | is_draining
-------------------+--------------------+-------
verticadb_node0001 | default_subcluster | f
verticadb_node0002 | default_subcluster | f
verticadb_node0003 | default_subcluster | f
verticadb_node0004 | analytics          | t
verticadb_node0005 | analytics          | t
verticadb_node0006 | analytics          | t