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MySQL 8.0.21 on CentOS8 uses almost all memory directly after start, non-tuned?
Posted by: Frederique Rijsdijk
Date: January 12, 2021 01:20PM

Hi -

I've recently installed my first MySQL 8.0.21 on a CentOS8 (latest updates), and noticed it seems to be using most of the memory on the machine, almost directly after a reboot. I've never seen this before with an untuned MySQL. So MySQL has no custom tuning, everything is default. Almost immediately after a reboot, I have about ~80MB free. If I disable MySQL from starting up, I'll have about 2.1GB of memory free.

If I'm quickly after a reboot, login (ssh), start top, I'll see the ~2GB of memory free, but this drops to the ~80MB in about 5 seconds. I see some changes to the mysql process in top in regards of memory usage, but nothing that reflects the amount of memory that's free on my system.

So this is a Vmware VM, running 4.18.0-240.1.1.el8_3.x86_64, 3GB of RAM, 2 cores (E5-2690 v3), running on VMware ESXi, 6.7.0, 16713306. I've done some hardening sysctls, installed apache, php etc, nothing fancy.

RPM: mysql-server-8.0.21-1.module_el8.2.0+493+63b41e36.x86_64
Repo: AppStream

Output of top (sort on RES memory with 'M') example, logged in as quick as I could, some memory is already gone:

top - 19:30:47 up 0 min,  1 user,  load average: 0.40, 0.08, 0.03
Tasks: 236 total,   3 running, 233 sleeping,   0 stopped,   0 zombie
%Cpu(s): 54.5 us, 30.3 sy,  0.0 ni,  3.0 id,  9.1 wa,  0.0 hi,  3.0 si,  0.0 st
MiB Mem :   2798.0 total,   1524.5 free,   1013.2 used,    260.4 buff/cache
MiB Swap:   1908.0 total,   1908.0 free,      0.0 used.   1620.6 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   1397 mysql     20   0  428840 260188  26924 S  16.7   9.1   0:02.16 mysqld
   1198 root      20   0  719396  50020  38244 S   0.0   1.7   0:00.21 php-fpm
   1211 root      20   0  426316  31292  16400 S   0.0   1.1   0:00.26 tuned
   1442 apache    20   0  733608  24128  12324 S   0.0   0.8   0:00.00 php-fpm
   1443 apache    20   0  733608  24128  12324 S   0.0   0.8   0:00.00 php-fpm
   1444 apache    20   0  733608  24128  12324 S   0.0   0.8   0:00.00 php-fpm
   1446 apache    20   0  733608  24128  12324 S   0.0   0.8   0:00.00 php-fpm
   1441 apache    20   0  733608  24124  12320 S   0.0   0.8   0:00.00 php-fpm
   1017 polkitd   20   0 1628176  22248  17364 S   0.0   0.8   0:00.13 polkitd
   1547 apache    20   0 1976548  22076   7664 S   0.0   0.8   0:00.22 httpd
   1546 apache    20   0 1845400  20008   7664 S   0.0   0.7   0:00.07 httpd

Three seconds later:

Tasks: 234 total,   1 running, 233 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.2 us,  0.2 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   2798.0 total,     88.1 free,   2466.9 used,    243.1 buff/cache
MiB Swap:   1908.0 total,   1904.0 free,      4.0 used.    169.6 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   1397 mysql     20   0 1773432 368564  34316 S   0.3  12.9   0:04.13 mysqld
   1198 root      20   0  719396  49364  37588 S   0.0   1.7   0:00.22 php-fpm
   1211 root      20   0  426316  30456  15564 S   0.0   1.1   0:00.27 tuned
   1442 apache    20   0  733608  23956  12152 S   0.0   0.8   0:00.00 php-fpm
   1443 apache    20   0  733608  23956  12152 S   0.0   0.8   0:00.00 php-fpm
   1444 apache    20   0  733608  23956  12152 S   0.0   0.8   0:00.00 php-fpm
   1446 apache    20   0  733608  23956  12152 S   0.0   0.8   0:00.00 php-fpm
   1441 apache    20   0  733608  23952  12148 S   0.0   0.8   0:00.00 php-fpm
   1547 apache    20   0 1976548  21912   7556 S   0.0   0.8   0:00.23 httpd

This is my /etc/my.cnf:

#
# This group is read both both by the client and the server
# use it for options that affect everything
#
[client-server]

#
# include all files from the config directory
#
!includedir /etc/my.cnf.d

.. and /etc/my.cnf.d is empty.

No databases, freshly initialized.

Strange thing as well is that I don't seem from top where my memory is going. The numbers (RES) add up to about 5-600MB of memory.

This can't be normal behaviour, is it?

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MySQL 8.0.21 on CentOS8 uses almost all memory directly after start, non-tuned?
January 12, 2021 01:20PM


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