Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual page 372

Chapter 22. Apache HTTP Server
The following section list directives found within the MPM-specific server-pool containers.
MaxClients
MaxClients sets a limit on the total number of server processes, or simultaneously connected
clients, that can run at one time. The main purpose of this directive is to keep a runaway Apache
HTTP Server from crashing the operating system. For busy servers this value should be set to
a high value. The server's default is set to 150 regardless of the MPM in use. However, it is not
recommended that the value for MaxClients exceeds 256 when using the prefork MPM.
MaxRequestsPerChild
MaxRequestsPerChild sets the total number of requests each child server process serves before
the child dies. The main reason for setting MaxRequestsPerChild is to avoid long-lived process
induced memory leaks. The default MaxRequestsPerChild for the prefork MPM is 4000 and for
the worker MPM is 0.
MinSpareServers and MaxSpareServers
These values are only used with the prefork MPM. They adjust how the Apache HTTP Server
dynamically adapts to the perceived load by maintaining an appropriate number of spare server
processes based on the number of incoming requests. The server checks the number of servers
waiting for a request and kills some if there are more than MaxSpareServers or creates some if the
number of servers is less than MinSpareServers.
The default MinSpareServers value is 5; the default MaxSpareServers value is 20. These default
settings should be appropriate for most situations. Be careful not to increase the MinSpareServers
to a large number as doing so creates a heavy processing load on the server even when traffic is light.
MinSpareThreads and MaxSpareThreads
These values are only used with the worker MPM. They adjust how the Apache HTTP Server
dynamically adapts to the perceived load by maintaining an appropriate number of spare server
threads based on the number of incoming requests. The server checks the number of server threads
waiting for a request and kills some if there are more than MaxSpareThreads or creates some if the
number of servers is less than MinSpareThreads.
The default MinSpareThreads value is 25; the default MaxSpareThreads value is 75. These
default settings should be appropriate for most situations. The value for MaxSpareThreads must be
greater than or equal to the sum of MinSpareThreads and ThreadsPerChild, else the Apache
HTTP Server automatically corrects it.
StartServers
The StartServers directive sets how many server processes are created upon startup. Since the
Web server dynamically kills and creates server processes based on traffic load, it is not necessary to
change this parameter. The Web server is set to start 8 server processes at startup for the prefork
MPM and 2 for the worker MPM.
ThreadsPerChild
This value is only used with the worker MPM. It sets the number of threads within each child process.
The default value for this directive is 25.
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