Turning on HugePages for an RDS for Oracle instance - Amazon Relational Database Service
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Turning on HugePages for an RDS for Oracle instance

Amazon RDS for Oracle supports Linux kernel HugePages for increased database scalability. HugePages results in smaller page tables and less CPU time spent on memory management, increasing the performance of large database instances. For more information, see Overview of HugePages in the Oracle documentation.

You can use HugePages with all supported versions and editions of RDS for Oracle.

The use_large_pages parameter controls whether HugePages are turned on for a DB instance. The possible settings for this parameter are ONLY, FALSE, and {DBInstanceClassHugePagesDefault}. The use_large_pages parameter is set to {DBInstanceClassHugePagesDefault} in the default DB parameter group for Oracle.

To control whether HugePages are turned on for a DB instance automatically, you can use the DBInstanceClassHugePagesDefault formula variable in parameter groups. The value is determined as follows:

  • For the DB instance classes mentioned in the table following, DBInstanceClassHugePagesDefault always evaluates to FALSE by default, and use_large_pages evaluates to FALSE. You can turn on HugePages manually for these DB instance classes if the DB instance class has at least 14 GiB of memory.

  • For DB instance classes not mentioned in the table following, if the DB instance class has less than 14 GiB of memory, DBInstanceClassHugePagesDefault always evaluates to FALSE. Also, use_large_pages evaluates to FALSE.

  • For DB instance classes not mentioned in the table following, if the instance class has at least 14 GiB of memory and less than 100 GiB of memory, DBInstanceClassHugePagesDefault evaluates to TRUE by default. Also, use_large_pages evaluates to ONLY. You can turn off HugePages manually by setting use_large_pages to FALSE.

  • For DB instance classes not mentioned in the table following, if the instance class has at least 100 GiB of memory, DBInstanceClassHugePagesDefault always evaluates to TRUE. Also, use_large_pages evaluates to ONLY and HugePages can't be disabled.

HugePages are not turned on by default for the following DB instance classes.

DB instance class family DB instance classes with HugePages not turned on by default

db.m5

db.m5.large

db.m4

db.m4.large, db.m4.xlarge, db.m4.2xlarge, db.m4.4xlarge, db.m4.10xlarge

db.t3

db.t3.micro, db.t3.small, db.t3.medium, db.t3.large

For more information about DB instance classes, see Hardware specifications for DB instance classes.

To turn on HugePages for new or existing DB instances manually, set the use_large_pages parameter to ONLY. You can't use HugePages with Oracle Automatic Memory Management (AMM). If you set the parameter use_large_pages to ONLY, then you must also set both memory_target and memory_max_target to 0. For more information about setting DB parameters for your DB instance, see Parameter groups for Amazon RDS.

You can also set the sga_target, sga_max_size, and pga_aggregate_target parameters. When you set system global area (SGA) and program global area (PGA) memory parameters, add the values together. Subtract this total from your available instance memory (DBInstanceClassMemory) to determine the free memory beyond the HugePages allocation. You must leave free memory of at least 2 GiB, or 10 percent of the total available instance memory, whichever is smaller.

After you configure your parameters, you must reboot your DB instance for the changes to take effect. For more information, see Rebooting a DB instance.

Note

The Oracle DB instance defers changes to SGA-related initialization parameters until you reboot the instance without failover. In the Amazon RDS console, choose Reboot but do not choose Reboot with failover. In the Amazon CLI, call the reboot-db-instance command with the --no-force-failover parameter. The DB instance does not process the SGA-related parameters during failover or during other maintenance operations that cause the instance to restart.

The following is a sample parameter configuration for HugePages that enables HugePages manually. You should set the values to meet your needs. 

memory_target            = 0
memory_max_target        = 0
pga_aggregate_target     = {DBInstanceClassMemory*1/8}
sga_target               = {DBInstanceClassMemory*3/4}
sga_max_size             = {DBInstanceClassMemory*3/4}
use_large_pages          = ONLY

Assume the following parameters values are set in a parameter group.

memory_target            = IF({DBInstanceClassHugePagesDefault}, 0, {DBInstanceClassMemory*3/4})
memory_max_target        = IF({DBInstanceClassHugePagesDefault}, 0, {DBInstanceClassMemory*3/4})
pga_aggregate_target     = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*1/8}, 0)
sga_target               = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*3/4}, 0)
sga_max_size             = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*3/4}, 0)
use_large_pages          = {DBInstanceClassHugePagesDefault}

The parameter group is used by a db.r4 DB instance class with less than 100 GiB of memory. With these parameter settings and use_large_pages set to {DBInstanceClassHugePagesDefault}, HugePages are turned on for the db.r4 instance.

Consider another example with following parameters values set in a parameter group.

memory_target           = IF({DBInstanceClassHugePagesDefault}, 0, {DBInstanceClassMemory*3/4})
memory_max_target       = IF({DBInstanceClassHugePagesDefault}, 0, {DBInstanceClassMemory*3/4})
pga_aggregate_target    = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*1/8}, 0)
sga_target              = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*3/4}, 0)
sga_max_size            = IF({DBInstanceClassHugePagesDefault}, {DBInstanceClassMemory*3/4}, 0)
use_large_pages         = FALSE

The parameter group is used by a db.r4 DB instance class and a db.r5 DB instance class, both with less than 100 GiB of memory. With these parameter settings, HugePages are turned off on the db.r4 and db.r5 instance.

Note

If this parameter group is used by a db.r4 DB instance class or db.r5 DB instance class with at least 100 GiB of memory, the FALSE setting for use_large_pages is overridden and set to ONLY. In this case, a customer notification regarding the override is sent.

After HugePages are active on your DB instance, you can view HugePages information by enabling enhanced monitoring. For more information, see Monitoring OS metrics with Enhanced Monitoring.