This Multi-Processing Module implements a non-threaded, pre-forking web server.
Status: MPM
Source File: prefork.c
Module Identifier:
mpm_prefork_module
This Multi-Processing Module (MPM) implements a non-threaded, pre-forking web server which handles request in a manner very similar to the default behavior of Apache 1.3 on Unix.
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.
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.
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. In addition, unless suexec is used, these directives also
set the privileges which will be inherited by CGI scripts.
MaxRequestsPerChild
controls how frequently the
server recycles processes by killing old ones and launching new
ones.
See also: Setting which addresses and ports Apache uses.
Syntax: AcceptMutex
default|method
Default: AcceptMutex
default
Context: server config
Status: core
The AcceptMutex
directives sets the method that
Apache uses to serialize multiple children accepting requests
on network sockets. Prior to Apache 2.0, the method was
selectable only at compile time. The optimal method to use is
highly architecture and platform dependent. For further
details, see the performance
tuning documentation.
If this directive is set to default
, then the
compile-time selected default will be used. Other possible
methods are listed below. Note that not all methods are
available on all platforms. If a method is specified which is
not available, a message will be written to the error log
listing the available methods.
flock
flock(2)
system call to lock the
file defined by the LockFile directive.fcntl
fnctl(2)
system call to lock the
file defined by the LockFile directive.sysvsem
pthread
MaxSpareServers
10
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.
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.
See also MinSpareServers and StartServers.
MinSpareServers
5
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.
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.
This directive has no effect on Microsoft Windows.
See also MaxSpareServers and StartServers.