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I am trying to figure out why my apache processes are eating so much memory

My slice specs( 1.5GB RAM, CentOS 5, Apache2, PHP 5.2, MySQL)

As you can see my top processes are consuming nearly half of my entire memory and when more processes are spawned the server nearly grinds to a halt, frequently going over into swap and crashing.

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND   
6817 apache    40   0  296m 103m 3920 S  0.0  6.7   0:03.52 httpd                         
6789 apache    40   0  295m 101m 3932 S  0.0  6.6   0:07.04 httpd                         
6765 apache    40   0  284m  91m 3948 S 55.1  5.9   0:12.45 httpd                         
6798 apache    40   0  284m  90m 3944 S  0.0  5.9   0:05.49 httpd                         
6542 apache    40   0  283m  90m 3956 S  0.0  5.8   0:43.25 httpd                         
6827 apache    40   0  283m  88m 3796 S  0.0  5.7   0:01.83 httpd

Does anyone have any clue what could be causing apache (and php) to be consuming so much memory?

              total       used       free     shared    buffers     cached
Mem:          1545        827        718          0          3        111
-/+ buffers/cache:        713        832
Swap:         3071        103       2968
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5 Answers 5

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2

You're almost certainly running mod_php, which means you're almost certainly running apache in mpm_prefork.

If performance is generally okay until load causes you to start swapping, a quick fix is to start throttling down apache's MaxClients. If apache is allowed to fork worker processes whenever it wants, it's going to start swapping under load. Requests will queue until a worker is available, so things can get slow, but not as slow as the death-by-swap.

If you really need to tune things tighter, consider getting away from prefork apache mpm. That means running PHP as FastCGI. If you're going to go with PHP under FastCGI, you should consider upgrading to PHP 5.3.3, which has much nicer FastCGI process manager (--enable-fpm configure option).

php-fpm/worker is much more memory efficient than old-fashioned mod_php. You can then tune the number of apache processes/threads independently of the number of PHP processes. And your memory-heavy PHP processes are only used for serving up php-driven content, and not wasted on serving static files.

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PID  USER   PR NI VIRT RES  SHR  S %CPU %MEM TIME+   COMMAND
6817 apache 40 0  296m 103m 3920 S 0.0  6.7  0:03.52 httpd
6789 apache 40 0  295m 101m 3932 S 0.0  6.6  0:07.04 httpd
6765 apache 40 0  284m 91m  3948 S 55.1 5.9  0:12.45 httpd
6798 apache 40 0  284m 90m  3944 S 0.0  5.9  0:05.49 httpd
6542 apache 40 0  283m 90m  3956 S 0.0  5.8  0:43.25 httpd
6827 apache 40 0  283m 88m  3796 S 0.0  5.7  0:01.83 httpd

Is wordpress the only thing running on apache? I'm curious mostly about the very high cpu usage of PID 6765 there. Wonder what it is doing. As far as the mem%s go, that looks pretty normal for a webapp setup, as each thread is actually running more than one worker.

What MPM are you using for apache, and how do you have it configured?

Also, if you're posting terminal dumps, please start each line with four spaces. It allows formatting to be preserved.

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1

My crystal ball is a bit dusty, but I guess you are using memcached and its PHP extension. If that's the case, try to disable it unless you really need the thing.

Another possibility is that you have some kind of op-code cache, such as XCache, installed, and have configured it to use a lot of memory.

You may try 

pmap -x `pidof apache`

to see what's consuming the memory.

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1

Memory figures for apache processes are pretty normal for a PHP setup. An highly tuned apache/php server here with many modules/extensions not loaded or even compiled usually runs between 200 and 350MiB of virtual memory per process, and 40~45MiB of resident memory per process.

You probably are not that familiar with the virtual memory subsystem? From what you're writing, your system is probably healty. Check the load average, you're ok with those memory figures unless that also goes high.

If you think it should stay forever at 0MiB swap, you're thinking wrong, that would be a really stupid thing for your operating system to do.

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1

Dont load unused apache modules (like python, perl, etc).

Use eAccelerator php module. It is php compiler. You can get faster execution and smaller memory usage.

Other users maybe also right.

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