Moodle in English: Server RAM usage increases after some time without any request

Server RAM usage increases after some time without any request

by Noé Ortega Quijano - Thursday, October 26, 2006, 5:05 PM

We have Moodle running on a server to make some tests. We hace noticed that the amount of RAM used increases as the time goes on. For example, if we reboot, we have 250 MB used of a total of 2GB. Some days later (3 or 4), leaving the server "alone" and with no requests at all, the amount of memory used is nearly 1GB. If we reboot, the problem dissapears, and we have again around 1750 MB free.

The solution seems to be changing something in the Apache configuration, but everything seems to be all right. The important settings are:

Timeout 120
KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 2
<IfModule prefork.c>
StartServers 8
MinSpareServers 8
MaxSpareServers 20
ServerLimit 256
MaxClients 256
MaxRequestsPerChild 4000
</IfModule>
<IfModule worker.c>
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 20
</IfModule>

<Directory "/var/www/html/moodle">
DirectoryIndex index.php
AcceptPathInfo on
AllowOverride None
Options None
Order allow,deny
Allow from all
</Directory>
Alias /moodle "/var/www/html/moodle"
AddOutputFilterByType DEFLATE text/html text/plain text/xml

The server is a Pentium D 830 with 2GB RAM. We are running Apache 2.0.52, MySQL 4.1.20, PHP 4.3.9, eAccelerator 0.9.3 and Moodle 1.6.3.

Some friends of mine have similar problems with other servers, so I guess this must be a relatively common problem.

Does anybody have any idea, suggestion or wathever? Thank you very much!

--Noé

Re: Server RAM usage increases after some time without any request

by Mikael Ekblom - Thursday, October 26, 2006, 5:22 PM

This could be due to some memory leak somewhere, either in the php or Apache process where memory is not deallocated. My first guess would be withinin php. You could try to upgrade your version of php. Do you by the way have Windows 2003 installed on this server or some *nix variant?

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Re: Server RAM usage increases after some time without any request

by Martín Langhoff - Thursday, October 26, 2006, 6:38 PM

No memory leak, but a side-effect of apache/php memory allocation strategies. Search this forum for posts on tuning apache, specifically for "maxclients"

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Re: Server RAM usage increases after some time without any request

by Noé Ortega Quijano - Thursday, October 26, 2006, 6:51 PM

Yes, it seems to be that kind of problem, but I have investigated and have no idea where it is... The OS is Red Hat EL 4.0. I have tried to upgrade the version of PHP, but I have the last stable version that up2date lets me.

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Re: Server RAM usage increases after some time without any request

by Stefan Kugler - Thursday, October 26, 2006, 6:08 PM

Hi!

It seems you are using Linux...
Linux uses RAM also for file caching, why not, when you have 2GB and 1750MB free. So your system may run faster.

Have a look at your system with "top" and "free", to get to know how many memory is "really" used and how many is used for cache. If swap also gets used, there is something wrong.

Here is an example, reboot yesterday in the morning, have a look at the cache values: see attached file.

Regards,
Stefan

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Re: Server RAM usage increases after some time without any request

by Noé Ortega Quijano - Thursday, October 26, 2006, 7:29 PM

Maxclients? I don't know, perhaps the problem has to do with that, but it is very strange because in fact the server has been "isolated" for days, without any incoming requests nor traffic at all.

Linux is using some memory for file caching, but it is only a small part of all the memory overhead that increases during the day (and during the night... always, little by little, but without stop). Here is the result of the top comand:

top - 14:07:54 up 1 day, 1:34, 1 user, load average: 0.07, 0.03, 0.01
Tasks: 67 total, 1 running, 66 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 2056168k total, 675732k used, 1380436k free, 99816k buffers
Swap: 4192924k total, 0k used, 4192924k free, 187620k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
[...]
6088 mysql 16 0 684m 117m 3928 S 0 5.8 0:00.24 mysqld
5869 apache 16 0 200m 38m 29m S 0 1.9 0:00.45 httpd
5873 apache 16 0 201m 25m 16m S 0 1.3 0:00.37 httpd
5872 apache 17 0 201m 25m 16m S 0 1.3 0:00.25 httpd
5868 apache 17 0 199m 24m 17m S 0 1.2 0:00.38 httpd
5870 apache 16 0 200m 24m 16m S 0 1.2 0:00.26 httpd
5874 apache 16 0 200m 22m 13m S 0 1.1 0:00.48 httpd
5877 apache 17 0 198m 17m 10m S 0 0.9 0:00.12 httpd
5871 apache 17 0 198m 16m 9928 S 0 0.8 0:00.13 httpd
5876 apache 17 0 198m 15m 9060 S 0 0.8 0:00.18 httpd
5875 apache 17 0 198m 15m 9072 S 0 0.8 0:00.15 httpd
[...]

Brainstorming needed

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Server RAM usage increases after some time without any request