Manage column store content manually

This page describes how to manage the content of the columnar engine's column store by manually adding and removing columns.

Based on your workload, you can manually add columns to the column store or drop some or all of the columns of a table or a materialized view from the column store. Query evaluation automatically uses the stored columnar data to answer queries.

When choosing which tables, materialized views and columns to add to the column store, consider both the size of the column store and the shape of the workload. Good candidates for selection include large tables or views that are frequently scanned. Within these tables or views, identify any large non-unique indexes used by the OLAP workload. You can add these indexes' columns to the column store and potentially drop the indexes, thereby eliminating the performance cost associated with their maintenance on the primary instance.

Use one of the following methods to manage the content of the columnar engine's column store:

• Manage column store content by updating database flags
• Manage column store content using SQL functions

See What data you can add to the column store for information about what data types and data sources you can use when adding tables, columns, and materialized views to the column store.

Before you begin

• You must have one of these IAM roles in the Google Cloud project you are using:
  • roles/alloydb.admin (the AlloyDB Admin predefined IAM role)
  • roles/owner (the Owner basic IAM role)
  • roles/editor (the Editor basic IAM role)

  If you don't have any of these roles, contact your Organization Administrator to request access.

Manage column store content by updating database flags

You can manage column store content manually by updating the google_columnar_engine.relations database flag. The flag has a single value that specifies all of your column store's data sources. During the restart, columns specified in this flag are automatically populated into the column store.

You can use this flag together with auto-columnarization. If the columnar engine has memory available after populating the columns you specify through the google_columnar_engine.relations flag, then auto-columnarization adds further columns to the column store, as needed.

For more information on setting an instance's database flags using either Google Cloud CLI or the Google Cloud console, see Configure an instance's database flags.

Add columns using flags

To add columns to the column store, define an instance's google_columnar_engine.relations flag. Set its value to a comma-separated list of items, with each item specifying a list of columns to include from a specific table, in this format:

DATABASE_NAME.SCHEMA_NAME.TABLE_NAME(COLUMN_LIST)

Replace the following:

• DATABASE_NAME: the database containing the columns to add to the column store.

• SCHEMA_NAME: the schema identifying the tables or the materialized views to add to the column store—for example, public.

• TABLE_NAME: the table or the materialized view containing the columns to add to the column store.

• COLUMN_LIST: a comma-separated list of the columns to add to the column store.

To add all of one table's or one materialized view's columns, omit the column list:

DATABASE_NAME.SCHEMA_NAME.TABLE_NAME

For more information on setting the database flags on an instance, see Configure an instance's database flags.

A note about command-line syntax

If you use the Google Cloud CLI to set the google_columnar_engine.relations flag, then you must use alternate delimiter syntax to separate the database flags that you set. This is because the column list is comma-separated, requiring you to use a non-comma character when specifying flags within the same command-line argument.

The following example demonstrates using the gcloud CLI to add two columns in the public schema to the column store. The example sets a separate flag to enable the columnar engine, because using the gcloud alloydb instance update command to set any database flag must also set all other database flags that you want to have non-default values, even if they're already set.

Caution: Running this example unsets all database flags from the instance except for the flags that it specifies.

gcloud alloydb instances update INSTANCE_NAME \
    --database-flags=^:^\
google_columnar_engine.relations='DATABASE_NAME.public.TABLE_NAME(COLUMN_1,COLUMN_2)'\
:google_columnar_engine.enabled=on\
[:FLAG_3=VALUE_3 ...] \
    --region=REGION_ID \
    --cluster=CLUSTER_ID

Drop columns using flags

To drop columns from the column store, set a new value for the google_columnar_engine.relations flag described in the previous section, leaving out the columns that you wish to drop.

To drop all of the columns from the column store, unset the google_columnar_engine.relations flag from your instance.

For more information on setting database flags on an instance, see Configure an instance's database flags.

Manage column store content using SQL functions

You can manage column store content manually by using SQL functions.

Add columns using SQL functions

Run the google_columnar_engine_add SQL function to add columns to the column store.

This method adds the specified columns to the column store and manages the columns in the connected node only. The new columns do not persist within the store across instance restarts.

This method does not change the google_columnar_engine.relations database flag. Auto columnarization does not consider columns added by this SQL function.

psql Client

SELECT google_columnar_engine_add(
    relation => 'TABLE_NAME',
    columns => 'COLUMN_LIST'
);

Replace the following:
• 'TABLE_NAME': A string containing the name of the table or the materialized view. If the table or the view is in a schema other than public, specify the name of the schema, a dot, and the name of the table or the view; for example, 'myschema.mytable'.
• 'COLUMN_LIST': A string containing a comma-separated, case-sensitive list of the names of the columns you want to add. If you want to add all of the table's or the materialized view's columns to the column store, omit this parameter.

Drop columns using SQL functions

Run the google_columnar_engine_drop SQL function as follows:

psql Client

SELECT google_columnar_engine_drop(
    relation => 'TABLE_NAME',
    columns => 'COLUMN_LIST'
);

Replace the following:

• 'TABLE_NAME': A string containing the name of the table or the materialized view. If the table or the view is in a schema other than public, specify the name of the schema, a dot, and the name of the table or the view; for example, 'myschema.mytable'.
• 'COLUMN_LIST': A string containing a comma-separated, case-sensitive list of the names of the columns you want to add. If you want to add all of the table's or the materialized view's columns to the column store, omit this parameter.

You can use the google_columnar_engine_drop function to remove columns added by editing the google_columnar_engine.relations database flag. However, when you do so, those columns will be added back to the columnar store when the instance is restarted.