Memory stress, Linux and NUMA

from the Artful MySQL Tips List


NUMA (non-uniform memory access) is a multiprocessing RAM design where each processor has “local” lower-latency RAM access. Linux has logic to analyse and optimise NUMA, but a DBMS managing a large database can challenge it with a single huge multi-threaded process consuming nearly all system memory, real and virtual. Running /proc/pic/numa_map exposes such difficulties, e.g., node 0 memory exhausted, other nodes underused, even when total available RAM should be sufficient. Jeremy Cole reports a solution for MySQL: 1. Force interleaved RAM allocation with numactl --interleave=all. 2. Flush Linux buffer caches and smooth out RAM allocation just before starting the MySQL server sysctl -q -w vm.drop_caches=3. 3. Force the OS to allocate the entire InnoDB buffer pool at with map_populate iv available, or memset. The Twitter MySQL 5.5 fork implements this solution as the mysqld_safe options numa-interleave and flush-caches, and the mysqld option innodb_buffer_pool_populate.

Last updated 31 Jul 2017


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