Oom

We recently had the situation that a customer complained about the Oom killer terminating the MariaDB database instance from time to time. The MariaDB database configuration was sized quit OK (about 50% of RAM was used for the database) but they did not have swap configured.

When we checked the memory for the specific mysqld process we found that VSZ was about 80 Gibyte (on a 64 Gibyte machine) and the RSS size was about 42 Gibyte. The very high VSZ value in combination with a lacking swap space and Oom …

# free
              total        used        free      shared  buff/cache   available
Mem:       16106332     3914228      367072      296508    11825032    11441608
Swap:      31250428      182924    31067504

# cat /proc/meminfo | grep ^Swap
SwapCached:        10056 kB
SwapTotal:      31250428 kB
SwapFree:       31067504 kB

# for file in /proc/*/status ; do
  awk '/VmSwap|Name/{
    if ( $2 != "0" )
      printf $2 " " $3
  }END{ print ""}' $file
done | grep kB | sort -k 2 …