Apache HTTP Server Version 2.2
Apache MPM event
| Description: | An experimental variant of the standard worker
MPM |
|---|---|
| Status: | MPM |
| Module Identifier: | mpm_event_module |
| Source File: | event.c |
Summary
Warning
This MPM is experimental, so it may or may not work as expected.
The event Multi-Processing Module (MPM) is
designed to allow more requests to be served simultaneously by
passing off some processing work to supporting threads, freeing up
the main threads to work on new requests. It is based on the
worker MPM, which implements a hybrid
multi-process multi-threaded server. Run-time configuration
directives are identical to those provided by
worker.
To use the event MPM, add
--with-mpm=event to the configure
script's arguments when building the httpd.
See also
How it Works
This MPM tries to fix the 'keep alive problem' in HTTP. After a client completes the first request, the client can keep the connection open, and send further requests using the same socket. This can save significant overhead in creating TCP connections. However, Apache traditionally keeps an entire child process/thread waiting for data from the client, which brings its own disadvantages. To solve this problem, this MPM uses a dedicated thread to handle both the Listening sockets, and all sockets that are in a Keep Alive state.
The MPM assumes that the underlying apr_pollset
implementation is reasonably threadsafe. This enables the MPM to
avoid excessive high level locking, or having to wake up the listener
thread in order to send it a keep-alive socket. This is currently
only compatible with KQueue and EPoll.
Requirements
This MPM depends on APR's atomic
compare-and-swap operations for thread synchronization. If you are
compiling for an x86 target and you don't need to support 386s, or
you are compiling for a SPARC and you don't need to run on
pre-UltraSPARC chips, add
--enable-nonportable-atomics=yes to the
configure script's arguments. This will cause
APR to implement atomic operations using efficient opcodes not
available in older CPUs.
This MPM does not perform well on older platforms which lack good threading, but the requirement for EPoll or KQueue makes this moot.
- To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
However, it is possible to run this MPM on FreeBSD 5.2.1, if you
use
libkse(seeman libmap.conf). - For NetBSD, at least version 2.0 is recommended.
- For Linux, a 2.6 kernel is recommended. It is also necessary to
ensure that your version of
glibchas been compiled with support for EPoll.