apache-performance-tuning

NOTE: the changes below (from the default ubuntu 8.04 LTS apache2 installation) brought memory usage down 
from 16MB per apache2 process to about 5MB AND reduced the number of process from 8 (for 1 user with 2 pages open)
to 3...

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Timeout

Lower the amount of time the server will wait before failing a request.
Timeout 45
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MaxKeepAliveRequests 100

KeepAliveTimeout 15

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prefork [default MPM for Apache 2.0 and 1.3]:

Apache 1.3-based.
Multiple processes, 1 thread per process, processes handle requests.
Used for security and stability.
Has higher memory consumption and lower performance over the newer Apache 2.0-based threaded MPMs.

worker:
Apache 2.0-based.
Multiple processes, many threads per process, threads handle requests.
Used for lower memory consumption and higher performance.
Does not provide the same level of isolation request-to-request, as a process-based MPM does.

DEFAULT CONFIGURATION

<IfModule prefork.c>
  StartServers            8
  MinSpareServers         5
  MaxSpareServers        20
  MaxClients            150
  MaxRequestsPerChild  1000
</IfModule>

<IfModule worker.c>
  StartServers            2
  MaxClients            150
  MinSpareThreads        25
  MaxSpareThreads        75 
  ThreadsPerChild        25
  MaxRequestsPerChild     0
</IfModule>

<IfModule mpm_winnt.c>
  ThreadsPerChild       250
  MaxRequestsPerChild     0
</IfModule>

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THESE SETTINGS DEPEND ON INTENDED PERFORMANCE, THIS IS FOR A LOW/MED END LOW UTILIZED SERVER...

<IfModule mpm_prefork_module>
    StartServers          2
    MinSpareServers       2
    MaxSpareServers       5
    MaxClients           50
    MaxRequestsPerChild   1000
</IfModule>


<IfModule mpm_worker_module>
    StartServers          2
    MaxClients           50
    MinSpareThreads       5
    MaxSpareThreads      25
    ThreadsPerChild      25
    MaxRequestsPerChild  1000
</IfModule>

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MaxClients ? (RAM - size_all_other_processes)/(size_apache_process)

KeepAlive

Enable HTTP persistent connections to improve latency times and reduce server load significantly [25% of original load is not uncommon].

prefork MPM:
KeepAlive On
KeepAliveTimeout 2
MaxKeepAliveRequests 80 

worker and winnt MPMs:
KeepAlive On
KeepAliveTimeout 15
MaxKeepAliveRequests 80

With the prefork MPM, it is recommended to set 'KeepAlive' to 'Off' otherwise a client will tie up an entire process 
for that span of time. 

Usually it's more useful to simply set the 'KeepAliveTimeout' value to something very low 
[2 seconds seems to be the ideal value]. 
This is not a problem with the worker MPM [thread-based], or under Windows [which only has the thread-based winnt MPM].

With the worker and winnt MPMs, the default 15 second timeout is setup to keep the connection open for the 
next page request; to better handle a client going from link to link. Check logs to see how long a client remains 
on each page before moving on to another link. Set value appropriately [do not set higher than 60 seconds].


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Directive MaxRequestsPerChild is used to recycle processes. When this directive is set to 0, an unlimited amount of requests are allowed per process.

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Set each "Directory" Directive to AlloOverride None unless you intend on using .htaccess

<Directory />
AllowOverride None
</Directory>


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http://www.devside.net/articles/apache-performance-tuning