Overview of parameter groups - Amazon Relational Database Service
Default and custom parameter groupsStatic and dynamic DB instance parametersStatic and dynamic DB cluster parametersCharacter set parametersSupported parameters and parameter values
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Overview of parameter groups

A DB parameter group acts as a container for engine configuration values that are applied to one or more DB instances.

DB cluster parameter groups apply to Multi-AZ DB clusters only. In a Multi-AZ DB cluster, the settings in the DB cluster parameter group apply to all of the DB instances in the cluster. The default DB parameter group for the DB engine and DB engine version is used for each DB instance in the DB cluster.

Default and custom parameter groups

If you create a DB instance without specifying a DB parameter group, the DB instance uses a default DB parameter group. Likewise, if you create a Multi-AZ DB cluster without specifying a DB cluster parameter group, the DB cluster uses a default DB cluster parameter group. Each default parameter group contains database engine defaults and Amazon RDS system defaults based on the engine, compute class, and allocated storage of the instance.

You can't modify the parameter settings of a default parameter group. Instead, you can do the following:

  1. Create a new parameter group.

  2. Change the settings of your desired parameters. Not all DB engine parameters in a parameter group are eligible to be modified.

  3. Modify your DB instance or DB cluster to associate the new parameter group.

    When you associate a new DB parameter group with a DB instance, the association happens immediately. For information about modifying a DB instance, see Modifying an Amazon RDS DB instance. For information about modifying a Multi-AZ DB clusters, see Modifying a Multi-AZ DB cluster.

    Note

    If you have modified your DB instance to use a custom parameter group, and you start the DB instance, RDS automatically reboots the DB instance as part of the startup process.

RDS applies the modified static and dynamic parameters in a newly associated parameter group only after the DB instance is rebooted. However, if you modify dynamic parameters in the DB parameter group after you associate it with the DB instance, these changes are applied immediately without a reboot. For more information about changing the DB parameter group, see Modifying an Amazon RDS DB instance.

If you update parameters within a DB parameter group, the changes apply to all DB instances that are associated with that parameter group. Likewise, if you update parameters within a Multi-AZ DB cluster parameter group, the changes apply to all Aurora DB clusters that are associated with that DB cluster parameter group.

If you don't want to create a parameter group from scratch, you can copy an existing parameter group with the Amazon CLI copy-db-parameter-group command or copy-db-cluster-parameter-group command. You might find that copying a parameter group is useful in some cases. For example, you might want to include most of an existing DB parameter group's custom parameters and values in a new DB parameter group.

Static and dynamic DB instance parameters

DB instance parameters are either static or dynamic. They differ as follows:

  • When you change a static parameter and save the DB parameter group, the parameter change takes effect after you manually reboot the associated DB instances. For static parameters, the console always uses pending-reboot for the ApplyMethod.

  • When you change a dynamic parameter, by default the parameter change takes effect immediately, without requiring a reboot. When you use the Amazon Web Services Management Console to change DB instance parameter values, it always uses immediate for the ApplyMethod for dynamic parameters. To defer the parameter change until after you reboot an associated DB instance, use the Amazon CLI or RDS API. Set the ApplyMethod to pending-reboot for the parameter change.

    Note

    Using pending-reboot with dynamic parameters in the Amazon CLI or RDS API on RDS for SQL Server DB instances generates an error. Use apply-immediately on RDS for SQL Server.

For more information about using the Amazon CLI to change a parameter value, see modify-db-parameter-group. For more information about using the RDS API to change a parameter value, see ModifyDBParameterGroup.

If a DB instance isn't using the latest changes to its associated DB parameter group, the console shows a status of pending-reboot for the DB parameter group. This status doesn't result in an automatic reboot during the next maintenance window. To apply the latest parameter changes to that DB instance, manually reboot the DB instance.

Static and dynamic DB cluster parameters

DB cluster parameters are either static or dynamic. They differ as follows:

  • When you change a static parameter and save the DB cluster parameter group, the parameter change takes effect after you manually reboot the associated DB clusters. For static parameters, the console always uses pending-reboot for the ApplyMethod.

  • When you change a dynamic parameter, by default the parameter change takes effect immediately, without requiring a reboot. When you use the Amazon Web Services Management Console to change DB cluster parameter values, it always uses immediate for the ApplyMethod for dynamic parameters. To defer the parameter change until after an associated DB cluster is rebooted, use the Amazon CLI or RDS API. Set the ApplyMethod to pending-reboot for the parameter change.

For more information about using the Amazon CLI to change a parameter value, see modify-db-cluster-parameter-group. For more information about using the RDS API to change a parameter value, see ModifyDBClusterParameterGroup.

Character set parameters

Before you create a DB instance or Multi-AZ DB cluster, set any parameters that relate to the character set or collation of your database in your parameter group. Also do so before you create a database in it. In this way, you ensure that the default database and new databases use the character set and collation values that you specify. If you change character set or collation parameters, the parameter changes aren't applied to existing databases.

For some DB engines, you can change character set or collation values for an existing database using the ALTER DATABASE command, for example:

ALTER DATABASE database_name CHARACTER SET character_set_name COLLATE collation;

For more information about changing the character set or collation values for a database, check the documentation for your DB engine.

Supported parameters and parameter values

To determine the supported parameters for your DB engine, view the parameters in the DB parameter group and DB cluster parameter group used by the DB instance or DB cluster. For more information, see Viewing parameter values for a DB parameter group and Viewing parameter values for a DB cluster parameter group.

In many cases, you can specify integer and Boolean parameter values using expressions, formulas, and functions. Functions can include a mathematical log expression. However, not all parameters support expressions, formulas, and functions for parameter values. For more information, see Specifying DB parameters.

Improperly setting parameters in a parameter group can have unintended adverse effects, including degraded performance and system instability. Always be cautious when modifying database parameters, and back up your data before modifying a parameter group. Try parameter group setting changes on a test DB instance or DB cluster before applying those parameter group changes to a production DB instance or DB cluster.