Improved `NUMA` support¶

In cases where the buffer pool memory allocation was bigger than size of the node, system would start swapping already allocated memory even if there is available memory on other node. This is would happen if the default NUMA memory allocation policy was selected. In that case system would favor one node more than other which caused the node to run out of memory. Changing the allocation policy to interleaving, memory will be allocated in round-robin fashion over the available node. This can be done by using the mysqld_safe numa_interleave option. NOTE: In order for this feature to work correctly mysqld_safe needs to be started as root.

Another improvement implemented is preallocating the pages in the buffer pool on startup with innodb_buffer_pool_populate variable. This forces NUMA allocation decisions to be made immediately while the buffer cache is clean.

It is generally recommended to enable all of the options together to maximize the performance effects on the NUMA architecture.

Version Specific Information¶

5.5.28-29.1

Improved NUMA support implemented. This feature was ported from Twitter’s MySQL patches.

System Variables¶

variable innodb_buffer_pool_populate¶

Command Line:	Yes
Config File:	Yes
Location:	mysqld
Scope:	Global
Dynamic:	No
Variable Type:	Boolean
Default Value:	0
Range:	0/1

When this variable is enabled, InnoDB preallocates pages in the buffer pool on startup to force NUMA allocation decisions to be made immediately while the buffer cache is clean.

Command-line Options for mysqld_safe¶

variable flush_caches¶

Command Line:	Yes
Config File:	Yes
Location:	mysqld_safe
Dynamic:	No
Variable Type:	Boolean
Default Value:	0
Range:	0/1

When enabled this will flush and purge buffers/caches before starting the server to help ensure NUMA allocation fairness across nodes. This option is useful for establishing a consistent and predictable behavior for normal usage and/or benchmarking.

variable numa_interleave¶

Command Line:	Yes
Config File:	Yes
Location:	mysqld_safe
Dynamic:	No
Variable Type:	Boolean
Default Value:	0
Range:	0/1

When this option is enabled, mysqld will run with its memory interleaved on all NUMA nodes by starting it with numactl --interleave=all. In case there is just 1 CPU/node, allocations will be “interleaved” between that node.