Altering subcluster settings

There are several settings you can alter on a subcluster using the ALTER SUBCLUSTER statement. You can also switch a subcluster from a primary to a secondary subcluster, or from a secondary to a primary.

Renaming a subcluster

To rename an existing subcluster, use the ALTER SUBCLUSTER statement's RENAME TO clause:

=> ALTER SUBCLUSTER default_subcluster RENAME TO load_subcluster;
ALTER SUBCLUSTER

=> SELECT DISTINCT subcluster_name FROM subclusters;
  subcluster_name
-------------------
 load_subcluster
 analytics_cluster
(2 rows)

Changing the default subcluster

The default subcluster designates which subcluster Vertica adds nodes to if you do not explicitly specify a subcluster when adding nodes to the database. When you create a new database (or when a database is upgraded from a version prior to 9.3.0) the default_subcluster is the default. You can find the current default subcluster by querying the is_default column of the SUBCLUSTERS system table.

The following example demonstrates finding the default subcluster, and then changing it to the subcluster named analytics_cluster:

=> SELECT DISTINCT subcluster_name FROM SUBCLUSTERS WHERE is_default = true;
  subcluster_name
--------------------
 default_subcluster
(1 row)

=> ALTER SUBCLUSTER analytics_cluster SET DEFAULT;
ALTER SUBCLUSTER
=> SELECT DISTINCT subcluster_name FROM SUBCLUSTERS WHERE is_default = true;
  subcluster_name
-------------------
 analytics_cluster
(1 row)

Converting a subcluster from primary to secondary, or secondary to primary

You usually choose whether a subcluster is primary or secondary when creating it (see Creating subclusters for more information). However, you can switch a subcluster between the two settings after you have created it. You may want to change whether a subcluster is primary or secondary to impact the K-safety of your database. For example, if you have a single primary subcluster that has down nodes that you cannot easily replace, you can promote a secondary subcluster to primary to ensure losing another primary node will not cause your database to shut down. On the oither hand, you may choose to convert a primary subcluster to a secondary before eventually shutting it down. This conversion can prevent the database from losing K-Safety if the subcluster you are shutting down contains half or more of the total number of primary nodes in the database.

To make a secondary subcluster into a primary subcluster, use the PROMOTE_SUBCLUSTER_TO_PRIMARY function:

=> SELECT DISTINCT subcluster_name, is_primary from subclusters;
  subcluster_name  | is_primary
-------------------+------------
 analytics_cluster | f
 load_subcluster   | t
(2 rows)


=> SELECT PROMOTE_SUBCLUSTER_TO_PRIMARY('analytics_cluster');
 PROMOTE_SUBCLUSTER_TO_PRIMARY
-------------------------------
 PROMOTE SUBCLUSTER TO PRIMARY
(1 row)


=> SELECT DISTINCT subcluster_name, is_primary from subclusters;
  subcluster_name  | is_primary
-------------------+------------
 analytics_cluster | t
 load_subcluster   | t
(2 rows)

Making a primary subcluster into a secondary subcluster is similar. Unlike converting a secondary subcluster to a primary, there are several issues that may prevent you from making a primary into a secondary. Vertica prevents you from making a primary into a secondary if any of the following is true:

• The subcluster contains a critical node.

• The subcluster is the only primary subcluster in the database. You must have at least one primary subcluster.

• The initiator node is a member of the subcluster you are trying to demote. You must call DEMOTE_SUBCLUSTER_TO_SECONDARY from another subcluster.

To convert a primary subcluster to secondary, use the DEMOTE_SUBCLUSTER_TO_SECONDARY function:

=> SELECT DISTINCT subcluster_name, is_primary from subclusters;
  subcluster_name  | is_primary
-------------------+------------
 analytics_cluster | t
 load_subcluster   | t
(2 rows)

=> SELECT DEMOTE_SUBCLUSTER_TO_SECONDARY('analytics_cluster');
 DEMOTE_SUBCLUSTER_TO_SECONDARY
--------------------------------
 DEMOTE SUBCLUSTER TO SECONDARY
(1 row)

=> SELECT DISTINCT subcluster_name, is_primary from subclusters;
  subcluster_name  | is_primary
-------------------+------------
 analytics_cluster | f
 load_subcluster   | t
(2 rows)