11.3.3. Common Multi-Processing Module Directives

The Multi-Processing Module (MPM) directives allow you to customize the behavior of a particular MPM specific server-pool. Since its characteristics differ depending on which MPM is used, the directives are embeded in IfModule. By default, the server-pool is defined for both the prefork and worker MPMs.

The following MPM directives are commonly used in /etc/httpd/conf/httpd.conf:

MaxClients

The MaxClients directive allows you to specify the maximum number of simultaneously connected clients to process at one time. It takes the following form:

MaxClients number

A high number can improve the performance of the server, although it is not recommended to exceed 256 when using the prefork MPM.

Example 11.71. Using the `MaxClients` directive

MaxClients 256

MaxRequestsPerChild

The MaxRequestsPerChild directive allows you to specify the maximum number of request a child process can serve before it dies. It takes the following form:

MaxRequestsPerChild number

Setting the number to 0 allows unlimited number of requests.

The MaxRequestsPerChild directive is used to prevent long-lived processes from causing memory leaks.

Example 11.72. Using the `MaxRequestsPerChild` directive

MaxRequestsPerChild 4000

MaxSpareServers

The MaxSpareServers directive allows you to specify the maximum number of spare child processes. It takes the following form:

MaxSpareServers number

This directive is used by the prefork MPM only.

Example 11.73. Using the `MaxSpareServers` directive

MaxSpareServers 20

MaxSpareThreads

The MaxSpareThreads directive allows you to specify the maximum number of spare server threads. It takes the following form:

MaxSpareThreads number

The number must be greater than or equal to the sum of MinSpareThreads and ThreadsPerChild. This directive is used by the worker MPM only.

Example 11.74. Using the `MaxSpareThreads` directive

MaxSpareThreads 75

MinSpareServers

The MinSpareServers directive allows you to specify the minimum number of spare child processes. It takes the following form:

MinSpareServers number

Note that a high number can create a heavy processing load on the server. This directive is used by the prefork MPM only.

Example 11.75. Using the `MinSpareServers` directive

MinSpareServers 5

MinSpareThreads

The MinSpareThreads directive allows you to specify the minimum number of spare server threads. It takes the following form:

MinSpareThreads number

This directive is used by the worker MPM only.

Example 11.76. Using the `MinSpareThreads` directive

MinSpareThreads 75

StartServers

The StartServers directive allows you to specify the number of child processes to create when the service is started. It takes the following form:

StartServers number

Since the child processes are dynamically created and terminated according to the current traffic load, it is usually not necessary to change this value.

Example 11.77. Using the `StartServers` directive

StartServers 8

ThreadsPerChild

The ThreadsPerChild directive allows you to specify the number of threads a child process can create. It takes the following form:

ThreadsPerChild number

This directive is used by the worker MPM only.

Example 11.78. Using the `ThreadsPerChild` directive

ThreadsPerChild 25