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I have tried to fix this but don't know enough, apparently. When I run top command I see that its filled with httpd processes. When this happens my site stops loading. It doesn't crash it just spins and spins. I am using prefork MPM. This looks like:

<IfModule prefork.c>
StartServers       1
MinSpareServers    5
#MinSpareServers    1
MaxSpareServers    10
#MaxSpareServers    5
ServerLimit        25
#ServerLimit        50
MaxClients        25
#MaxClients        50
#MaxRequestsPerChild  10000
MaxRequestsPerChild  100
</IfModule>

This problem started with the defaults which are commented out. I then tried to make changes thinking that it would help if I lower the MaxClients because I have about 1gb ram available. I thought the default MaxClients was to high because the average memory usage per httpd process is 55mb. Here is a screenshot of top, keep in mind this doesn't show all the httpd processes.

top - 09:48:27 up 42 days,  3:13,  1 user,  load average: 1.09, 1.09, 1.09
Tasks:  35 total,   3 running,  32 sleeping,   0 stopped,   0 zombie
Cpu(s): 14.7%us,  0.5%sy,  0.0%ni, 84.8%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   2097152k total,  1134676k used,   962476k free,        0k buffers
Swap:        0k total,        0k used,        0k free,        0k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                        
 1649 root      17   0  315m 122m  14m S  0.0  6.0   1:51.67 java                                                                                            
27755 mysql     18   0  204m  71m 5744 S  4.0  3.5 806:09.08 mysqld                                                                                          
23603 apache    15   0 76404  51m 5900 S  0.0  2.5   0:20.21 httpd                                                                                           
20408 apache    15   0 77124  51m 5252 S  0.0  2.5   0:25.57 httpd                                                                                           
28026 apache    16   0 76788  50m 5240 R 97.7  2.5   0:05.15 httpd                                                                                           
24497 apache    16   0 76272  50m 5484 S  0.0  2.5   0:06.55 httpd                                                                                           
27724 apache    15   0 76380  50m 5268 S  0.0  2.5   0:04.81 httpd                                                                                           
21561 apache    15   0 75672  50m 5532 S  0.0  2.4   0:28.54 httpd                                                                                           
26537 apache    16   0 75116  49m 5488 R 19.9  2.4   0:10.09 httpd                                                                                           
28027 apache    15   0 75080  49m 5216 S  0.0  2.4   0:03.07 httpd                                                                                           
24498 apache    15   0 74180  49m 5656 S  0.0  2.4   0:12.33 httpd                                                                                           
21934 apache    15   0 74568  48m 5256 S  0.0  2.4   0:27.48 httpd                                                                                           
24484 apache    15   0 74152  48m 5260 S  0.0  2.4   0:17.70 httpd                                                                                           
28012 apache    15   0 73248  47m 5208 S  0.0  2.3   0:02.34 httpd                                                                                           
13428 root      18   0 37032  15m 8456 S  0.0  0.8   0:00.21 httpd

What am I doing wrong?

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1  
Just as an FYI, just because each httpd is using 58M of RAM doesn't mean that 51M isn't the same 51M each other httpd is using. Linux does a lot of shared library loading behind the scenes and apache makes use of shared memory in general. –  Kyle Smith Jan 21 '11 at 18:02
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1 Answer

Looks to me like you have a code issue, which you're trying to control through the MPM parameters.

Some of those parameters are counter productive, specilaly MaxClients and MaxRequestPerChild, they won't help you lower the load, on the contrary they'll get it higher.

Also remember that top is showing the virtual memory allocation, in no case that means that each apache is really using 50mb of memory, to get more accurate statistics you can activate mod_status by adding this to your config

<Location /server-status>
    SetHandler server-status
    Order deny,allow
    Deny from all
    Allow from 127.0.0.1
</Location>

Just to give you an example, here's my config on a regular apache server under heavy load

StartServers       32
MinSpareServers    10
MaxSpareServers   20
ServerLimit      8192
MaxClients       4096
MaxRequestsPerChild  9000

What worries me most is that single httpd instance running at 97% CPU, this shows that the code running on apache is doing something quite nasty, I would rather get that investigated because you're just trying to control the situation (wisely) by lowering your prefork parameters but the only way to solve the issue is to tackle the main problem.

Good luck! Apache code issues are always a pain :/

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ok thx for the insight. I tried <Location /server-status> SetHandler server-status Order deny,allow Deny from all Allow from 127.0.0.1 </Location> but I get a 403 forbidden error when I go to domain.com/server-status –  Chris Jan 24 '11 at 19:30
    
Check that you're connecting to localhost, otherwise you need to change the Allow From line –  lynxman Jan 24 '11 at 19:38
    
i changed the allow from to my ip address and then i had to add a virtualhost. once im done ima delete the virtual host and deny all again. thanks for your help –  Chris Jan 25 '11 at 22:33
    
Excellent! Glad to see it worked fine –  lynxman Jan 25 '11 at 23:03
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