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Parameter reference for Aurora PostgreSQL query plan management

You can set your preferences for the apg_plan_mgmt extension by using the parameters listed in this section. These are available in the custom DB cluster parameter and the DB parameter group associated with your Aurora PostgreSQL DB cluster. These parameters control the behavior of the query plan management feature and how it affects the optimizer. For information about setting up query plan management, see Turning on Aurora PostgreSQL query plan management. Changing the parameters following has no effect if the apg_plan_mgmt extension isn't set up as detailed in that section. For information about modifying parameters, see Modifying parameters in a DB cluster parameter group in Amazon Aurora and DB parameter groups for Amazon Aurora DB instances.

apg_plan_mgmt.capture_plan_baselines

Captures query execution plans generated by the optimizer for each SQL statement and stores them in the dba_plans view. By default, the maximum number of plans that can be stored is 10,000 as specified by the apg_plan_mgmt.max_plans parameter. For reference information, see apg_plan_mgmt.max_plans.

You can set this parameter in the custom DB cluster parameter group or in the custom DB parameter group. Changing the value of this parameter doesn't require a reboot.

For more information, see Capturing Aurora PostgreSQL execution plans.

apg_plan_mgmt.plan_capture_threshold

Specifies a threshold so that if the total cost of the query execution plan is below the threshold, the plan won’t be captured in the apg_plan_mgmt.dba_plans view.

Changing the value of this parameter doesn't require a reboot.

For more information, see Examining Aurora PostgreSQL query plans in the dba_plans view.

apg_plan_mgmt.explain_hashes

Specifies if the EXPLAIN [ANALYZE] shows sql_hash and plan_hash at the end of its output. Changing the value of this parameter doesn't require a reboot.

apg_plan_mgmt.log_plan_enforcement_result

Specifies if the results has to be recorded to see if the QPM managed plans are used properly. When a stored generic plan is used, there will be no records written in the log files. Changing the value of this parameter doesn't require a reboot.

apg_plan_mgmt.max_databases

Specifies the maximum number of databases on your Aurora PostgreSQL DB cluster's Writer instance that can use query plan management. By default, up to 10 databases can use query plan management. If you have more than 10 databases on the instance, you can change the value of this setting. To find out how many databases are on a given instance, connect to the instance using psql. Then, use the psql metacommand, \l, to list the databases.

Changing the value of this parameter requires that you reboot the instance for the setting to take effect.

You can set this parameter in the custom DB cluster parameter group or in the custom DB parameter group.

apg_plan_mgmt.max_plans

Sets the maximum number of SQL statements that the query plan manager can maintain in the apg_plan_mgmt.dba_plans view. We recommend setting this parameter to 10000 or higher for all Aurora PostgreSQL versions.

You can set this parameter in the custom DB cluster parameter group or in the custom DB parameter group. Changing the value of this parameter requires that you reboot the instance for the setting to take effect.

For more information, see Examining Aurora PostgreSQL query plans in the dba_plans view.

apg_plan_mgmt.plan_hash_version

Specifies the use cases that the plan_hash calculation is designed to cover. A higher version of apg_plan_mgmt.plan_hash_version covers all the functionality of the lower version. For example, version 3 covers the use cases supported by version 2.

Changing the value of this parameter must be followed by a call to apg_plan_mgmt.validate_plans('update_plan_hash'). It updates the plan_hash values in each database with apg_plan_mgmt installed and entries in the plans table. For more information, see Validating plans

apg_plan_mgmt.plan_retention_period

Specifies the number of days to keep plans in the apg_plan_mgmt.dba_plans view, after which they're automatically deleted. By default, a plan is deleted when 32 days have elapsed since the plan was last used (the last_used column in the apg_plan_mgmt.dba_plans view). You can change this setting to any number, 1 and over.

Changing the value of this parameter requires that you reboot the instance for the setting to take effect.

For more information, see Examining Aurora PostgreSQL query plans in the dba_plans view.

apg_plan_mgmt.unapproved_plan_execution_threshold

Specifies a cost threshold below which an Unapproved plan can be used by the optimizer. By default the threshold is 0, so the optimizer doesn't run Unapproved plans. Setting this parameter to a trivially low cost threshold such as 100 avoids plan enforcement overhead on trivial plans. You can also set this parameter to an extremely large value like 10000000 using the reactive style of plan management. This allows the optimizer to use all chosen plans with no plan enforcement overhead. But, when a bad plan is found, you can manually mark it as "rejected" so that it is not used next time.

The value of this parameter represents a cost estimate for running a given plan. If an Unapproved plan is below that estimated cost, the optimizer uses it for the SQL statement. You can see captured plans and their status (Approved, Unapproved) in the dba_plans view. To learn more, see Examining Aurora PostgreSQL query plans in the dba_plans view.

Changing the value of this parameter doesn't require a reboot.

For more information, see Using Aurora PostgreSQL managed plans.

apg_plan_mgmt.use_plan_baselines

Specifies that the optimizer should use one of the Approved plans captured and stored in the apg_plan_mgmt.dba_plans view. By default, this parameter is off (false), causing the optimizer to use the minimum-cost plan that it generates without any further assessment. Turning this parameter on (setting it to true) forces the optimizer to choose a query execution plan for the statement from its plan baseline. For more information, see Using Aurora PostgreSQL managed plans. To find an image detailing this process, see How the optimizer chooses which plan to run.

You can set this parameter in the custom DB cluster parameter group or in the custom DB parameter group. Changing the value of this parameter doesn't require a reboot.

You can evaluate response times of different captured plans and change plan status, as needed. For more information, see Improving Aurora PostgreSQL query plans.

auto_explain.hashes

Specifies if the auto_explain output shows sql_hash and plan_hash. Changing the value of this parameter doesn't require a reboot.