This Multi-Processing Module implements a hybrid multi-threaded multi-process web server.
Status: MPM
Source File: threaded.c
Module Identifier:
mpm_threaded_module
This Multi-Processing Module (MPM) is the default for most unix-like operating systems. It implements a hybrid multi-process multi-threaded server. Each process has a fixed number of threads. The server adjusts to handle load by increasing or decreasing the number of processes.
A single control process is responsible for launching child
processes. Each child process creates a fixed number of threads
as specified in the ThreadsPerChild directive. The
individual threads then listen for connections and serve them
when they arrive.
Apache always tries to maintain a pool of spare or
idle server threads, which stand ready to serve incoming
requests. In this way, clients do not need to wait for a new
threads or processes to be created before their requests can be
served. Apache assesses the total number of idle threads in all
processes, and forks or kills processes to keep this number
within the boundaries specified by MinSpareThreads
and MaxSpareThreads. Since this process is very
self-regulating, it is rarely necessary to modify these
directives from their default values. The maximum number of
clients that may be served simultaneously is determined by
multiplying the maximum number of server processes that will be
created (MaxClients) by the number of threads
created in each process (ThreadsPerChild).
While the parent process is usually started as root under
Unix in order to bind to port 80, the child processes and
threads 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.