How many CPU sockets? Is NUMA exposed? This could be MySQL/MariaDB "swapping insanity".
On Mon, Sep 23, 2024 at 2:44 PM cyusedfzfb via discuss <[email protected]> wrote: > > Hi all! > > New here, signed up just new, to discuss an interesting mariadb behaviour we > are seeing, related to mariadb unexpectedly using swap space. > > Look at this example: > > RHEL 8.10, running mariadb-server-utils.x86_64 > 3:10.5.22-1.module+el8.8.0+20134+a92c7654: > > [user@db ~]$ free -g > total used free shared buff/cache > available > Mem: 187 9 11 0 165 > 175 > Swap: 3 3 0 > > and: > > top - 08:52:46 up 39 days, 15:50, 2 users, load average: 1.70, 2.05, 1.99 > Tasks: 616 total, 2 running, 614 sleeping, 0 stopped, 0 zombie > %Cpu(s): 6.0 us, 0.8 sy, 0.0 ni, 88.2 id, 4.7 wa, 0.1 hi, 0.1 si, 0.0 > st > MiB Mem : 191529.7 total, 11761.7 free, 9764.9 used, 170003.1 buff/cache > MiB Swap: 4096.0 total, 1006.1 free, 3089.9 used. 179429.5 avail Mem > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ > COMMAND SWAP > 1952811 mysql 20 0 14.4g 5.0g 15172 S 65.7 2.7 9663:14 mysqld > 1.7g > 2934963 root 20 0 5208 2056 1408 S 8.9 0.0 10:39.29 gzip > 0 > 2934962 root 20 0 33612 8268 6960 S 7.9 0.0 2:35.31 > mysqldump 0 > > while: > > [user@db ~]$ cat /proc/sys/vm/swappiness > 1 > > We could (we should..) allocate more ram to mariadb, but the point is: there > is plenty of RAM available, and there always has been, since boot. And yet, > mariadb is using all swap. > > I guess this has no performance impact, probably the swapped pages are not > actually used, but zabbix does not like 100% swap usage. And frankly: neither > do I. > > Why? Can anyone here explain? Swappiness set to 1...is mariadb ignoring > swappiness..? Is there something else we can configure..? > > I read some older posts on ram/swap, and here is some data, requested in that > older thread: > > [user@db ~]$ sudo ps -o pid,vsz,comm `pgrep mysqld` > PID VSZ COMMAND > 1952811 15117612 mysqld > > and > > [user@db ~]$ for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " > " $3}END{ > > print ""}' $file; done | sort -k 2 -n -r | grep mysql > mysqld 1982672 kB > > > We are seeing similar behaviour on another machines, running more recent > mariadb version: 10.5.22-MariaDB MariaDB Server: > > [user@db_another ~]$ free -g > total used free shared buff/cache > available > Mem: 62 40 0 1 21 > 20 > Swap: 4 3 1 > > Again: enough RAM available, and swap is used 3/4, mostly by MariaDB. > > > Hope the provided information is enough. Let me know if there is anything > else I can provide. Looking forward for any insight or help on the matter. :-) > > Thanks! > MJ > > > _______________________________________________ > discuss mailing list -- [email protected] > To unsubscribe send an email to [email protected] _______________________________________________ discuss mailing list -- [email protected] To unsubscribe send an email to [email protected]
