This Multi-Processing Module implements a hybrid multi-process multi-threaded web server with a variable number of threads per process.
Status: MPM
Source File: dexter.c
Module Identifier: mpm_dexter_module
This Multi-Processing Module (MPM) implements a hybrid multi-process, multi-threaded web server. A fixed number of processes create threads to handle requests. Fluctuations in load are handled by increasing or decreasing the number of threads in each process.
A single control process launches the number of child processes
indicated by the NumServers directive at server startup.
Each child process creates threads as specified in the
StartThreads 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 new threads to be created. For
each child process, Apache assesses the number of idle threads and
creates or destroys threads 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 number
of server processes that will be created (NumServers) by
the maximum number of threads created in each process
(MaxThreadsPerChild).
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.