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
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