Understanding NUMA and Its Impact on MySQL Performance

Background – The discussion originated from a client’s doubt about disabling the NUMA setting when preparing a server for MySQL deployment, prompting an investigation into NUMA.

NUMA Overview – NUMA (Non‑Uniform Memory Access) partitions hardware resources into nodes, each with its own CPU and memory; memory access is fastest within the local node and slower across nodes.

NUMA and MySQL Analysis

Default: memory always allocated on the local node.

Bind: forces allocation to a specified node.

Interleave: distributes memory across all or selected nodes.

Preferred: tries a specified node first, then others.

Because MySQL is a single‑process, multi‑threaded system, it can only use memory from the node where its process runs. In NUMA‑enabled servers, this can lead to “swap insanity” where a MySQL instance exhausts its node’s memory, causing swapping even though other nodes have free memory.

Example: a 40 GB MySQL server with the process bound to a node that only has 20 GB local memory will swap the excess 10 GB to disk, degrading performance.

How to Disable NUMA

1. Hardware level : Turn off NUMA in the BIOS.

2. OS kernel level : Add numa=off to the Linux kernel boot parameters and reboot.

For RHEL 6 edit # vi /boot/grub/grub.conf and add kernel /vmlinuz-2.6.39-400.215.10.EL ro root=/dev/VolGroup00/LogVol00 numa=off .

For RHEL 7 edit # vi /etc/default/grub and set GRUB_CMDLINE_LINUX="... numa=off" , then rebuild the GRUB config with # grub2-mkconfig -o /etc/grub2.cfg .

3. Database level : Start MySQL with # numactl --interleave=all ./bin/mysqld_safe --defaults-file=/etc/my.cnf & to force interleaved memory allocation.

innodb_numa_interleave Parameter – Introduced in MySQL 5.6.27/5.7.9, this parameter makes MySQL set its NUMA policy to interleaved automatically, provided the server supports NUMA and MySQL is compiled with WITH_NUMA . Note that the binary packages before MySQL 5.7.17 do not support this option.

Testing results:

If the system lacks NUMA support, compiling with -DWITH_NUMA=ON fails.

MySQL 5.7.19+ binary packages include support for innodb_numa_interleave .

Recommendations

• For dedicated MySQL servers, disable NUMA via BIOS or kernel settings.

• If other workloads need NUMA, keep it enabled and use a MySQL version that supports innodb_numa_interleave .

Common Misconception: Not finding the numactl command means NUMA is disabled. In fact, numactl is an optional Linux utility for inspecting and tuning NUMA; its absence does not indicate that NUMA is off.

References

"The MySQL “swap insanity” problem and the effects of the NUMA architecture" – https://blog.jcole.us/2010/09/28/mysql-swap-insanity-and-the-numa-architect "A brief update on NUMA and MySQL" – https://blog.jcole.us/2012/04/16/a-brief-update-on-numa-and-mysql/ Linux NUMA documentation – https://www.kernel.org/doc/html/v4.18/vm/numa.html Additional guides – https://www.thegeekdiary.com/how-to-disable-numa-in-centos-rhel-67/ and others.