Specifying DB parameters - Amazon Aurora
DB parameter formulasDB parameter functionsDB parameter log expressionsDB parameter value examples

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.

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.

DBInstanceClassMemory

Returns an integer for the number of bytes of memory available to the database process. This number is internally calculated by starting with the total amount of memory for the DB instance class. From this, the calculation subtracts 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 Aurora DB instance classes. The exact value depends on a combination of factors. These include instance class, DB engine, and whether it applies to an RDS instance or an instance that's part of an Aurora cluster.

EndPointPort

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

TrueIfReplica

Returns 1 if the DB instance is a read replica and 0 if it is not. This is the default value for the read_only parameter in Aurora MySQL.

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.

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.

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.

DB parameter value examples

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

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 LEAST

You can specify the LEAST function in an Aurora MySQL table_definition_cache parameter value. Use it to set the number of table definitions that can be stored in the definition cache to the lesser of DBInstanceClassMemory/393040 or 20,000.

LEAST({DBInstanceClassMemory/393040}, 20000)