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MySQLd - Memory staying high

Posted August 24, 2015 14.6k views
UbuntuMySQLServer OptimizationConfiguration Management

Hello guys!

I have a problem om my 1GB Droplet with ‘mysqld’:

The droplet is configured via ServerPilot and everything works just fine.

My only problem is that when the server is being used (+50 users on the same time) the memory will go up, and use almost 900mb of RAM. I guess it’s cool, and the sites work fast and so on (Also got SWAP file in case) but my problem is that the memory wont go down again (To like 200-300 MB RAM). Is this normal behavior?

If I use ’htop’ I get the following:

 PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
 1077 mysql      20   0  868M  103M  3124 S  3.3 10.4  3:12.34 /usr/sbin/mysqld
 1173 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:03.92 /usr/sbin/mysqld
 1174 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:06.79 /usr/sbin/mysqld
 1175 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:04.96 /usr/sbin/mysqld
 1176 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:05.67 /usr/sbin/mysqld
 1177 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:06.64 /usr/sbin/mysqld
 1178 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:04.03 /usr/sbin/mysqld
 1179 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:05.08 /usr/sbin/mysqld
 1180 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:04.96 /usr/sbin/mysqld
 1181 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:06.41 /usr/sbin/mysqld
 1182 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:06.78 /usr/sbin/mysqld
 1190 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:11.25 /usr/sbin/mysqld
 1191 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:15.42 /usr/sbin/mysqld
 1192 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:01.02 /usr/sbin/mysqld
 1193 mysql      20   0  868M  103M  3124 S  3.3 10.4  0:24.00 /usr/sbin/mysqld
 1215 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:00.00 /usr/sbin/mysqld
 1337 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:15.42 /usr/sbin/mysqld
 1421 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:20.37 /usr/sbin/mysqld
 1705 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:13.58 /usr/sbin/mysqld
 2464 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:18.78 /usr/sbin/mysqld
 2467 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:13.16 /usr/sbin/mysqld
11823 mysql      20   0  868M  103M  3124 S  0.0 10.4  0:03.01 /usr/sbin/mysqld

As you can see the /usr/sbin/mysqld is there a lot, and uses a lot of memory, even when no users are using the sites (I have 2 sites on the droplet) - Side question: why is there so many instances?

My /var/log/mysql.log is empty - Is this normal? Is there anything I can do to get it to log anything? Delete the file? (It’s 0 bytes)
Same applies for my syslog

If you need more information, I’ll be more than happy to asist.

Thank you very much!

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2 answers
jsamuel August 24, 2015

Hi,

The MySQL processes in that list are actually different threads. In htop’s settings, you can configure it to not show separate threads for each process which can make it much simpler and more useful to look at. So, what you’re seeing there is really MySQL using 10.4% of your server’s memory.

As memory is increasing when you have many concurrent requests, the memory increase is likely due to the additional PHP processes that are needed to handle the requests. When a request comes in but there are no available PHP worker processes for the app (that is, they are all busy handling a request), PHP-FPM will create an additional process for the new request. If your request concurrency later goes down, after a period of time PHP-FPM will kill any PHP processes that have been idle (not needed to handle requests) and memory usage will go down.

For more information on memory usage on ServerPilot and ways to reduce memory usage, see here:

https://serverpilot.io/community/articles/how-to-reduce-php-and-wordpress-memory-usage.html

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  • Zonax7100 August 25, 2015

    Hi jsamuel.

    Thank you for a great and detailed answer. I appreciate it.

    The tip for htop is great, much more simple!

    But with the memory, the problem seems to be that the memory wont go down, when it first got up.
    So even if there is no traffic at all, the memory still uses a lot (More than shown above normally)
    How long time should I wait for it to get back to normal?

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jsamuel August 25, 2015

I’m glad the htop suggestion helped. That’s the first thing I change in htop on any new server of my own.

Regarding the memory usage remaining high, I suggest opening a support ticket with ServerPilot. There’s almost certainly a good explanation for what you’re seeing but it will take more information and possibly us looking directly at your server to determine it.

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