Working with DB parameter groups

Database parameters specify how the database is configured. For example, database parameters can specify the amount of resources, such as memory, to allocate to a database.

You manage your database configuration by associating your DB instances with parameter groups. Amazon RDS defines parameter groups with default settings.

Important

You can define your own parameter groups with customized settings. Then you can modify your DB instances to use your own parameter groups.

For information about modifying a DB instance, see Modifying an Amazon RDS DB instance.

Note

Some DB engines offer additional features that you can add to your database as options in an option group. For information about option groups, see Working with option groups.

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

If you create a DB instance without specifying a DB parameter group, the DB instance uses a default DB parameter group. Each default DB 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 create your own parameter group where you choose your own parameter settings. Not all DB engine parameters can be changed in a parameter group that you create.

If you want to use your own parameter group, you create a new parameter group and modify the parameters that you want to. You then modify your DB instance to use the new parameter group. If you update parameters within a DB parameter group, the changes apply to all DB instances that are associated with that parameter group.

You can copy an existing DB parameter group with the AWS CLI copy-db-parameter-group command. Copying a parameter group can be convenient when you want to include most of an existing DB parameter group's custom parameters and values in a new DB parameter group.

Here are some important points about working with parameters in a DB parameter group:

• Database parameters are either static or dynamic. When you change a static parameter and save the DB parameter group, the parameter change takes effect after you manually reboot the DB instance. You can reboot a DB instance using the RDS console, by calling the reboot-db-instance CLI command, or by calling the RebootDBInstance API operation. The requirement to reboot the associated DB instance after a static parameter change helps mitigate the risk of a parameter misconfiguration affecting an API call, such as calling ModifyDBInstance to change DB instance class or scale storage.

  When you change a dynamic parameter and save the DB parameter group, the change is applied to the parameter group immediately regardless of the Apply Immediately setting. If you use the pending-reboot setting in the AWS CLI or RDS API, the change is still applied to the parameter group immediately. However, applying the parameter change to DB instances that use the parameter group requires a reboot.

  Note

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

  If a DB instance isn't using the latest changes to its associated DB parameter group, the AWS Management Console shows the DB parameter group with a status of pending-reboot. The pending-reboot parameter groups 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.

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

• You can specify integer and Boolean parameters using expressions, formulas, and functions. Functions can include a mathematical log expression. For more information, see Specifying DB parameters.

• Set any parameters that relate to the character set or collation of your database in your parameter group before creating the DB instance and before you create a database in your DB instance. This ensures that the default database and new databases in your DB instance use the character set and collation values that you specify. If you change character set or collation parameters for your DB instance, the parameter changes are not 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.

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

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

Creating a DB parameter group

You can create a new DB parameter group using the AWS Management Console, the AWS CLI, or the RDS API.

Console

To create a DB parameter group

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

3. Choose Create parameter group.

   The Create parameter group window appears.

4. In the Parameter group family list, select a DB parameter group family.

5. In the Type list, select DB Parameter Group.

6. In the Group name box, enter the name of the new DB parameter group.

7. In the Description box, enter a description for the new DB parameter group.

8. Choose Create.

AWS CLI

To create a DB parameter group, use the AWS CLI create-db-parameter-group command. The following example creates a DB parameter group named mydbparametergroup for MySQL version 5.6 with a description of "My new parameter group."

Include the following required parameters:

• --db-parameter-group-name

• --db-parameter-group-family

• --description

To list all of the available parameter group families, use the following command:

aws rds describe-db-engine-versions --query "DBEngineVersions[].DBParameterGroupFamily"				
			

Note

The output contains duplicates.

Example

For Linux, macOS, or Unix:

aws rds create-db-parameter-group \
    --db-parameter-group-name mydbparametergroup \
    --db-parameter-group-family MySQL5.6 \
    --description "My new parameter group"

For Windows:

aws rds create-db-parameter-group ^
    --db-parameter-group-name mydbparametergroup ^
    --db-parameter-group-family MySQL5.6 ^
    --description "My new parameter group"

This command produces output similar to the following:

DBPARAMETERGROUP  mydbparametergroup  mysql5.6  My new parameter group

RDS API

To create a DB parameter group, use the RDS API CreateDBParameterGroup operation.

Include the following required parameters:

• DBParameterGroupName

• DBParameterGroupFamily

• Description

Associating a DB parameter group with a DB instance

You can create your own DB parameter groups with customized settings. You can associate a DB parameter group with a DB instance using the AWS Management Console, the AWS CLI, or the RDS API. You can do so when you create or modify a DB instance.

For information about creating a DB parameter group, see Creating a DB parameter group. For information about creating a DB instance, see Creating an Amazon RDS DB instance. For information about modifying a DB instance, see Modifying an Amazon RDS DB instance.

Note

When you associate a new DB parameter group with a DB instance, the modified static and dynamic parameters are applied only after the DB instance is rebooted. However, if you modify dynamic parameters in the newly associated DB parameter group, these changes are applied immediately without a reboot.

Console

To associate a DB parameter group with a DB instance

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Databases, and then choose the DB instance that you want to modify.

3. Choose Modify. The Modify DB Instance page appears.

4. Change the DB parameter group setting.

5. Choose Continue and check the summary of modifications.

6. (Optional) Choose Apply immediately to apply the changes immediately. Choosing this option can cause an outage in some cases. For more information, see Using the Apply Immediately setting.

7. On the confirmation page, review your changes. If they are correct, choose Modify DB instance to save your changes.

   Or choose Back to edit your changes or Cancel to cancel your changes.

AWS CLI

To associate a DB parameter group with a DB instance, use the AWS CLI modify-db-instance command with the following options:

• --db-instance-identifier

• --db-parameter-group-name

The following example associates the mydbpg DB parameter group with the database-1 DB instance. The changes are applied immediately by using --apply-immediately. Use --no-apply-immediately to apply the changes during the next maintenance window. For more information, see Using the Apply Immediately setting.

Example

For Linux, macOS, or Unix:

aws rds modify-db-instance \
    --db-instance-identifier database-1 \
    --db-parameter-group-name mydbpg \
    --apply-immediately

For Windows:

aws rds modify-db-instance ^
    --db-instance-identifier database-1 ^
    --db-parameter-group-name mydbpg ^
    --apply-immediately

RDS API

To associate a DB parameter group with a DB instance, use the RDS API ModifyDBInstance operation with the following parameters:

• DBInstanceName

• DBParameterGroupName

Modifying parameters in a DB parameter group

You can modify parameter values in a customer-created DB parameter group; you can't change the parameter values in a default DB parameter group. Changes to parameters in a customer-created DB parameter group are applied to all DB instances that are associated with the DB parameter group.

Changes to some parameters are applied to the DB instance immediately without a reboot. Changes to other parameters are applied only after the DB instance is rebooted. The RDS console shows the status of the DB parameter group associated with a DB instance on the Configuration tab. For example, if the DB instance isn't using the latest changes to its associated DB parameter group, the RDS console shows the DB parameter group with a status of pending-reboot. To apply the latest parameter changes to that DB instance, manually reboot the DB instance.

Console

To modify a DB parameter group

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

3. In the list, choose the parameter group that you want to modify.

4. For Parameter group actions, choose Edit.

5. Change the values of the parameters that you want to modify. You can scroll through the parameters using the arrow keys at the top right of the dialog box.

   You can't change values in a default parameter group.

6. Choose Save changes.

AWS CLI

To modify a DB parameter group, use the AWS CLI modify-db-parameter-group command with the following required options:

• --db-parameter-group-name

• --parameters

The following example modifies the max_connections and max_allowed_packet values in the DB parameter group named mydbparametergroup.

Example

For Linux, macOS, or Unix:

aws rds modify-db-parameter-group \
    --db-parameter-group-name mydbparametergroup \
    --parameters "ParameterName=max_connections,ParameterValue=250,ApplyMethod=immediate" \
                 "ParameterName=max_allowed_packet,ParameterValue=1024,ApplyMethod=immediate"

For Windows:

aws rds modify-db-parameter-group ^
    --db-parameter-group-name mydbparametergroup ^
    --parameters "ParameterName=max_connections,ParameterValue=250,ApplyMethod=immediate" ^
                 "ParameterName=max_allowed_packet,ParameterValue=1024,ApplyMethod=immediate"

The command produces output like the following:

DBPARAMETERGROUP  mydbparametergroup

RDS API

To modify a DB parameter group, use the RDS API ModifyDBParameterGroup operation with the following required parameters:

• DBParameterGroupName

• Parameters

Resetting parameters in a DB parameter group to their default values

You can reset parameter values in a customer-created DB parameter group to their default values. Changes to parameters in a customer-created DB parameter group are applied to all DB instances that are associated with the DB parameter group.

When you use the console, you can reset specific parameters to their default values, but you can't easily reset all of the parameters in the DB parameter group at once. When you use the AWS CLI or RDS API, you can reset specific parameters to their default values, and you can reset all of the parameters in the DB parameter group at once.

Changes to some parameters are applied to the DB instance immediately without a reboot. Changes to other parameters are applied only after the DB instance is rebooted. The RDS console shows the status of the DB parameter group associated with a DB instance on the Configuration tab. For example, if the DB instance isn't using the latest changes to its associated DB parameter group, the RDS console shows the DB parameter group with a status of pending-reboot. To apply the latest parameter changes to that DB instance, manually reboot the DB instance.

Note

In a default DB parameter group, parameters are always set to their default values.

Console

To reset parameters in a DB parameter group to their default values

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

3. In the list, choose the parameter group.

4. For Parameter group actions, choose Edit.

5. Choose the parameters that you want to reset to their default values. You can scroll through the parameters using the arrow keys at the top right of the dialog box.

   You can't reset values in a default parameter group.

6. Choose Reset and then confirm by choosing Reset parameters.

AWS CLI

To reset some or all of the parameters in a DB parameter group, use the AWS CLI reset-db-parameter-group command with the following required option: --db-parameter-group-name.

To reset all of the parameters in the DB parameter group, specify the --reset-all-parameters option. To reset specific parameters, specify the --parameters option.

The following example resets all of the parameters in the DB parameter group named mydbparametergroup to their default values.

Example

For Linux, macOS, or Unix:

aws rds reset-db-parameter-group \
    --db-parameter-group-name mydbparametergroup \
    --reset-all-parameters

For Windows:

aws rds reset-db-parameter-group ^
    --db-parameter-group-name mydbparametergroup ^
    --reset-all-parameters

The following example resets the max_connections and max_allowed_packet options to their default values in the DB parameter group named mydbparametergroup.

Example

For Linux, macOS, or Unix:

aws rds reset-db-parameter-group \
    --db-parameter-group-name mydbparametergroup \
    --parameters "ParameterName=max_connections,ApplyMethod=immediate" \
                 "ParameterName=max_allowed_packet,ApplyMethod=immediate"

For Windows:

aws rds reset-db-parameter-group ^
    --db-parameter-group-name mydbparametergroup ^
    --parameters "ParameterName=max_connections,ApplyMethod=immediate" ^
                 "ParameterName=max_allowed_packet,ApplyMethod=immediate"

The command produces output like the following:

DBParameterGroupName  mydbparametergroup

RDS API

To reset parameters in a DB parameter group to their default values, use the RDS API ResetDBParameterGroup command with the following required parameter: DBParameterGroupName.

To reset all of the parameters in the DB parameter group, set the ResetAllParameters parameter to true. To reset specific parameters, specify the Parameters parameter.

Copying a DB parameter group

You can copy custom DB parameter groups that you create. Copying a parameter group is a convenient solution when you have already created a DB parameter group and you want to include most of the custom parameters and values from that group in a new DB parameter group. You can copy a DB parameter group by using the AWS Management Console, the AWS CLI copy-db-parameter-group command, or the RDS API CopyDBParameterGroup operation.

After you copy a DB parameter group, wait at least 5 minutes before creating your first DB instance that uses that DB parameter group as the default parameter group. Doing this allows Amazon RDS to fully complete the copy action before the parameter group is used. This is especially important for parameters that are critical when creating the default database for a DB instance. An example is the character set for the default database defined by the character_set_database parameter. Use the Parameter Groups option of the Amazon RDS console or the describe-db-parameters command to verify that your DB parameter group is created.

Note

You can't copy a default parameter group. However, you can create a new parameter group that is based on a default parameter group.

Currently, you can't copy a parameter group to a different AWS Region.

Console

To copy a DB parameter group

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

3. In the list, choose the custom parameter group that you want to copy.

4. For Parameter group actions, choose Copy.

5. In New DB parameter group identifier, enter a name for the new parameter group.

6. In Description, enter a description for the new parameter group.

7. Choose Copy.

AWS CLI

To copy a DB parameter group, use the AWS CLI copy-db-parameter-group command with the following required options:

• --source-db-parameter-group-identifier

• --target-db-parameter-group-identifier

• --target-db-parameter-group-description

The following example creates a new DB parameter group named mygroup2 that is a copy of the DB parameter group mygroup1.

Example

For Linux, macOS, or Unix:

aws rds copy-db-parameter-group \
    --source-db-parameter-group-identifier mygroup1 \
    --target-db-parameter-group-identifier mygroup2 \
    --target-db-parameter-group-description "DB parameter group 2"

For Windows:

aws rds copy-db-parameter-group ^
    --source-db-parameter-group-identifier mygroup1 ^
    --target-db-parameter-group-identifier mygroup2 ^
    --target-db-parameter-group-description "DB parameter group 2"

RDS API

To copy a DB parameter group, use the RDS API CopyDBParameterGroup operation with the following required parameters:

• SourceDBParameterGroupIdentifier

• TargetDBParameterGroupIdentifier

• TargetDBParameterGroupDescription

Listing DB parameter groups

You can list the DB parameter groups you've created for your AWS account.

Note

Default parameter groups are automatically created from a default parameter template when you create a DB instance for a particular DB engine and version. These default parameter groups contain preferred parameter settings and can't be modified. When you create a custom parameter group, you can modify parameter settings.

Console

To list all DB parameter groups for an AWS account

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

   The DB parameter groups appear in a list.

AWS CLI

To list all DB parameter groups for an AWS account, use the AWS CLI describe-db-parameter-groups command.

Example

The following example lists all available DB parameter groups for an AWS account.

aws rds describe-db-parameter-groups

The command returns a response like the following:

DBPARAMETERGROUP  default.mysql5.6     mysql5.6  Default parameter group for MySQL5.6
DBPARAMETERGROUP  mydbparametergroup   mysql5.6  My new parameter group

The following example describes the mydbparamgroup1 parameter group.

For Linux, macOS, or Unix:

aws rds describe-db-parameter-groups \
    --db-parameter-group-name mydbparamgroup1

For Windows:

aws rds describe-db-parameter-groups ^
    --db-parameter-group-name mydbparamgroup1

The command returns a response like the following:

DBPARAMETERGROUP  mydbparametergroup1  mysql5.6  My new parameter group

RDS API

To list all DB parameter groups for an AWS account, use the RDS API DescribeDBParameterGroups operation.

Viewing parameter values for a DB parameter group

You can get a list of all parameters in a DB parameter group and their values.

Console

To view the parameter values for a DB parameter group

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

   The DB parameter groups appear in a list.

3. Choose the name of the parameter group to see its list of parameters.

AWS CLI

To view the parameter values for a DB parameter group, use the AWS CLI describe-db-parameters command with the following required parameter.

• --db-parameter-group-name

Example

The following example lists the parameters and parameter values for a DB parameter group named mydbparametergroup.

aws rds describe-db-parameters --db-parameter-group-name mydbparametergroup

The command returns a response like the following:

DBPARAMETER  Parameter Name            Parameter Value  Source           Data Type  Apply Type  Is Modifiable
DBPARAMETER  allow-suspicious-udfs                      engine-default   boolean    static      false
DBPARAMETER  auto_increment_increment                   engine-default   integer    dynamic     true
DBPARAMETER  auto_increment_offset                      engine-default   integer    dynamic     true
DBPARAMETER  binlog_cache_size         32768            system           integer    dynamic     true
DBPARAMETER  socket                    /tmp/mysql.sock  system           string     static      false

RDS API

To view the parameter values for a DB parameter group, use the RDS API DescribeDBParameters command with the following required parameter.

• DBParameterGroupName

Comparing DB parameter groups

You can use the AWS Management Console to view the differences between two parameter groups for the same DB engine and version.

To compare two parameter groups

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the navigation pane, choose Parameter groups.

3. In the list, choose the two parameter groups that you want to compare.

4. For Parameter group actions, choose Compare.

   Note

   If the items you selected aren't equivalent, you can't choose Compare. For example, you can't compare a MySQL 5.6 and a MySQL 5.7 parameter group. You can't compare a DB parameter group and an Aurora DB cluster parameter group.

Specifying DB parameters

DB parameter types include the following:

• Integer

• Boolean

• String

• Long

• Double

• Timestamp

• Object of other defined data types

• Array of values of type integer, Boolean, string, long, double, timestamp, or object

You can also specify integer and Boolean parameters using expressions, formulas, and functions.

For the Oracle engine, you can use the DBInstanceClassHugePagesDefault formula variable to specify a Boolean DB parameter. See DB parameter formula variables.

For the PostgreSQL engine, you can use an expression to specify a Boolean DB parameter. See Boolean DB parameter expressions.

Contents

• DB parameter formulas
  • DB parameter formula variables
  • DB parameter formula operators
• DB parameter functions
• Boolean DB parameter expressions
• DB parameter log expressions
• DB parameter value examples

DB parameter formulas

A DB parameter formula is an expression that resolves to an integer value or a Boolean value. You enclose the expression in braces: {}. You can use a formula for either a DB parameter value or as an argument to a DB parameter function.

Syntax

{FormulaVariable}
{FormulaVariable*Integer}
{FormulaVariable*Integer/Integer}
{FormulaVariable/Integer}

DB parameter formula variables

Each formula variable returns an integer or a Boolean value. The names of the variables are case-sensitive.

AllocatedStorage

Returns an integer representing the size, in bytes, of the data volume.

DBInstanceClassHugePagesDefault

Returns a Boolean value. Currently, it's only supported for Oracle engines.

For more information, see Enabling HugePages for an Oracle DB instance.

DBInstanceClassMemory

Returns an integer for the number of bytes of memory available to the database process. This number is internally calculated by taking the total amount of memory for the DB instance class and subtracting memory reserved for the operating system and the RDS processes that manage the instance. Therefore, the number is always somewhat lower than the memory figures shown in the instance class tables in DB instance classes. The exact value depends on a combination of instance class, DB engine, and whether it applies to an RDS instance or an instance that's part of an Aurora cluster.

DBInstanceVCPU

Returns an integer representing the number of virtual central processing units (vCPUs) used by Amazon RDS to manage the instance. Currently, it's only supported for the PostgreSQL engine.

EndPointPort

Returns an integer representing the port used when connecting to the DB instance.

DB parameter formula operators

DB parameter formulas support two operators: division and multiplication.

Division operator: /

Divides the dividend by the divisor, returning an integer quotient. Decimals in the quotient are truncated, not rounded.

Syntax

dividend / divisor

The dividend and divisor arguments must be integer expressions.

Multiplication operator: *

Multiplies the expressions, returning the product of the expressions. Decimals in the expressions are truncated, not rounded.

Syntax

expression * expression

Both expressions must be integers.

DB parameter functions

You specify the arguments of DB parameter functions as either integers or formulas. Each function must have at least one argument. Specify multiple arguments as a comma-separated list. The list can't have any empty members, such as argument1,,argument3. Function names are case-insensitive.

IF

Returns an argument.

Currently, it's only supported for Oracle engines, and the only supported first argument is {DBInstanceClassHugePagesDefault}. For more information, see Enabling HugePages for an Oracle DB instance.

Syntax

IF(argument1, argument2, argument3)

Returns the second argument if the first argument evaluates to true. Returns the third argument otherwise.

GREATEST

Returns the largest value from a list of integers or parameter formulas.

Syntax

GREATEST(argument1, argument2,...argumentn)

Returns an integer.

LEAST

Returns the smallest value from a list of integers or parameter formulas.

Syntax

LEAST(argument1, argument2,...argumentn)

Returns an integer.

SUM

Adds the values of the specified integers or parameter formulas.

Syntax

SUM(argument1, argument2,...argumentn)

Returns an integer.

Boolean DB parameter expressions

A Boolean DB parameter expression resolves to a Boolean value of 1 or 0. The expression is enclosed in quotation marks.

Note

Boolean DB parameter expressions are only supported for the PostgreSQL engine.

Syntax

"expression operator expression"

Both expressions must resolve to integers. An expression can be the following:

• integer constant

• DB parameter formula

• DB parameter function

• DB parameter variable

Boolean DB parameter expressions support the following inequality operators:

The greater than operator: >

Syntax

"expression > expression"

The less than operator: <

Syntax

"expression < expression"

The greater than or equal to operators: >=, =>

Syntax

"expression >= expression"
"expression => expression"

The less than or equal to operators: <=, =<

Syntax

"expression <= expression"
"expression =< expression"

Example using a Boolean DB parameter expression

The following Boolean DB parameter expression example compares the result of a parameter formula with an integer to modify the Boolean DB parameter wal_compression for a PostgreSQL DB instance. The parameter expression compares the number of vCPUs with the value 2. If the number of vCPUs is greater than 2, then the wal_compression DB parameter is set to true.

aws rds modify-db-parameter-group --db-parameter-group-name group-name \
--parameters "ParameterName=wal_compression,ParameterValue=\"{DBInstanceVCPU} > 2\" "

DB parameter log expressions

You can set an integer DB parameter value to a log expression. You enclose the expression in braces: {}. For example:

{log(DBInstanceClassMemory/8187281418)*1000}

The log function represents log base 2. This example also uses the DBInstanceClassMemory formula variable. See DB parameter formula variables.

Note

Currently, you can't specify the MySQL innodb_log_file_size parameter with any value other than an integer.

DB parameter value examples

These examples show using formulas, functions, and expressions for the values of DB parameters.

Note

DB Parameter functions are currently supported only in the console and aren't supported in the AWS CLI.

Warning

Improperly setting parameters in a DB parameter group can have unintended adverse effects. These might include degraded performance and system instability. Use caution when modifying database parameters and back up your data before modifying your DB parameter group. Try out parameter group changes on a test DB instance, created using point-in-time-restores, before applying those parameter group changes to your production DB instances.

Example using the DB parameter function GREATEST

You can specify the GREATEST function in an Oracle processes parameter. Use it to set the number of user processes to the larger of either 80 or DBInstanceClassMemory divided by 9,868,951.

GREATEST({DBInstanceClassMemory/9868951},80)

Example using the DB parameter function LEAST

You can specify the LEAST function in a MySQL max_binlog_cache_size parameter value. Use it to set the maximum cache size a transaction can use in a MySQL instance to the lesser of 1 MB or DBInstanceClass/256.

LEAST({DBInstanceClassMemory/256},10485760)