Columnar engine flags

This page describes the database flags that AlloyDB for PostgreSQL uses to enable and manage features specific to its columnar engine. For a list of all database flags that AlloyDB supports, see Supported database flags.

Flags marked with Instance restarts mean that AlloyDB restarts an instance whenever you set, remove, or modify this flag on that instance. The flag's value persists for the instance until you modify it again.

Enablement

google_columnar_engine.enabled

Type	Boolean
Default	off
Instance restarts	Yes

If on, enables the AlloyDB columnar engine.

Auto-columnarization

google_columnar_engine.enable_auto_columnarization

Type	Boolean
Default	on
Instance restarts	No

If on, enables the columnar engine's auto-columnarization features.

google_columnar_engine.relations

Type	String
Default	An empty string
Instance restarts	No

Specifies a list of columns for AlloyDB to add to your cluster's column store, apart from auto-columnarization. These columns can come from any tables within your cluster.

The flag's value is formatted as a comma-separated list of items. Each item specifies one or more columns from a single table, expressed in this format:

'DATABASE_NAME.SCHEMA_NAME.TABLE_NAME(COLUMN_LIST)'

For more information, see Manage column store content manually.

google_columnar_engine.auto_columnarization_schedule

Type	String
Default	An empty string
Instance restarts	No

Specifies the frequency that AlloyDB runs its auto-columnarization process on the instance.

The value is a string in this format:

'EVERY NUMBER TIME_UNITS'

Replace the following:

• NUMBER: A positive integer.

• TIME_UNITS: Either DAYS or HOURS.

If not defined, then AlloyDB runs the auto-columnarization process once every hour.

Sizing and query processing

google_columnar_engine.memory_size_in_mb

Type	Integer
Valid values	From 128 to 70% of instance memory
Default	30% of instance memory
Instance restarts	Yes

The amount of instance memory, expressed in mebibytes (MiB), that AlloyDB allocates to the column store.

If this flag is not set, then AlloyDB allocates 30% of the instance's memory to the column store.

google_columnar_engine.enable_columnar_scan

Type	Boolean
Default	on
Instance restarts	No

If on, allows AlloyDB to access data in the column store when handling queries.

If this flag is off while google_columnar_engine.enabled is on, then the columnar engine stays enabled and retains its column store, but AlloyDB does not use columnar data when handling queries.

Population and refresh

google_columnar_engine.refresh_threshold_percentage

Type	Integer
Valid values	1 ... 100
Default	50
Instance restarts	No

Specifies the column store's data-refresh threshold, expressed as a percentage.

AlloyDB refreshes the data within a columnar unit—a set of data blocks within a columnar table—when all of these conditions are met:

• The columnar unit's table has exceeded the scan-threshold defined by the separate refresh_threshold_scan_count flag.

• The percentage of the columnar unit's underlying data blocks that have become invalid exceeds the value of the refresh_threshold_percentage flag. Columnar data blocks become invalid due to changes in the row-based data that the columnar table draws upon.

google_columnar_engine.refresh_threshold_scan_count

Type	Integer
Valid values	0 ... 2147483647
Default	5
Instance restarts	No

AlloyDB keeps a running count of the table scans performed on each columnar table since that table's most recent DML query. The value of the refresh_threshold_scan_count flag specifies the minimum value of this counter on any columnar table before AlloyDB can refresh its data. From there, AlloyDB uses the invalid-block threshold defined by refresh_threshold_percentage to determine when to refresh the table's data.

If this flag's value is set to 0, then AlloyDB disregards table scans to determine when to refresh columnar data, using only refresh_threshold_percentage instead.

google_job_scheduler.maintenance_cpu_percentage

Note: This flag uses the prefix google_job_scheduler and not google_columnar_engine.

Type	Integer
Valid values	0 ... 100
Default	20
Instance restarts	No

The maximum percentage of an instance's CPU capacity that the columnar engine can apply to background processing.

google_job_scheduler.max_parallel_workers_per_job

Note: This flag uses the prefix google_job_scheduler and not google_columnar_engine.

Type	Integer
Valid values	0 ... 262143
Default	2
Instance restarts	No

The maximum number of parallel workers that the columnar engine can create to handle any single background processing operation.

Vectorized join

google_columnar_engine.enable_vectorized_join

Preview

This product or feature is subject to the "Pre-GA Offerings Terms" in the General Service Terms section of the Service Specific Terms. Pre-GA products and features are available "as is" and might have limited support. For more information, see the launch stage descriptions.

Type	Boolean
Default	off
Restarts instance	No

If on, then AlloyDB automatically uses multithreaded vectorized operations to improve the performance of queries that join multiple tables.

For more information, see Enable vectorized joins.

google_columnar_engine.vectorized_join_threads

Preview

This product or feature is subject to the "Pre-GA Offerings Terms" in the General Service Terms section of the Service Specific Terms. Pre-GA products and features are available "as is" and might have limited support. For more information, see the launch stage descriptions.

Type	Integer
Valid values	Up to half of the instance's vCPU count
Default	1
Restarts instance	No

Defines the maximum number of parallel threads available to the vectorized join operator, enabled by the enable_vectorized_join flag.

You can define a value as large as one-half of the instance's vCPUs. For example, on a 16 vCPU instance, this flag's maximum value is 8.