Apache MPM prefork

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Description:	Implements a non-threaded, pre-forking web server
Status:	MPM
Module Identifier:	mpm_prefork_module
Source File:	prefork.c

Summary

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This Multi-Processing Module (MPM) implements a non-threaded, - pre-forking web server that handles requests in a manner similar - to Apache 1.3. It is appropriate for sites that need to avoid - threading for compatibility with non-thread-safe libraries. It - is also the best MPM for isolating each request, so that a problem - with a single request will not affect any other.

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This MPM is very self-regulating, so it is rarely necessary to - adjust its configuration directives. Most important is that - MaxClients be big enough to - handle as many simultaneous requests as you expect to receive, but - small enough to assure that there is enough physical RAM for all - processes.

Directives

Topics

How it Works

How it Works

A single control process is responsible for launching child - processes which listen for connections and serve them when they - arrive. Apache always tries to maintain several spare - or idle server processes, which stand ready to serve incoming - requests. In this way, clients do not need to wait for a new - child processes to be forked before their requests can be - served.

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The StartServers, - MinSpareServers, - MaxSpareServers, and - MaxClients regulate how - the parent process creates children to serve requests. In general, - Apache is very self-regulating, so most sites do not need to - adjust these directives from their default values. Sites which - need to serve more than 256 simultaneous requests may need to - increase MaxClients, - while sites with limited memory may need to decrease MaxClients to keep the server from - thrashing (swapping memory to disk and back). More information - about tuning process creation is provided in the performance hints - documentation.

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While the parent process is usually started as root - under Unix in order to bind to port 80, the child processes are - launched by Apache as a less-privileged user. The User and Group directives are used to set - the privileges of the Apache child processes. The child processes - must be able to read all the content that will be served, but - should have as few privileges beyond that as possible.

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MaxRequestsPerChild - controls how frequently the server recycles processes by killing - old ones and launching new ones.

MaxSpareServers Directive

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Description:	Maximum number of idle child server processes
Syntax:	`MaxSpareServers number`
Default:	`MaxSpareServers 10`
Context:	server config
Status:	MPM
Module:	prefork

The MaxSpareServers directive sets the - desired maximum number of idle child server processes. An - idle process is one which is not handling a request. If there are - more than MaxSpareServers idle, then the - parent process will kill off the excess processes.

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Tuning of this parameter should only be necessary on very - busy sites. Setting this parameter to a large number is almost - always a bad idea. If you are trying to set the value lower than - MinSpareServers, Apache - will automatically adjust it to MinSpareServers + 1.

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MinSpareServers Directive

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Description:	Minimum number of idle child server processes
Syntax:	`MinSpareServers number`
Default:	`MinSpareServers 5`
Context:	server config
Status:	MPM
Module:	prefork

The MinSpareServers directive sets the - desired minimum number of idle child server processes. An - idle process is one which is not handling a request. If there are - fewer than MinSpareServers idle, then the parent - process creates new children at a maximum rate of 1 per second.

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Tuning of this parameter should only be necessary on very - busy sites. Setting this parameter to a large number is almost - always a bad idea.

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Apache MPM prefork

Summary

Directives

Topics

See also

How it Works

MaxSpareServers Directive

See also

MinSpareServers Directive

See also