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Apache module mod_mmap_static
[APACHE DOCUMENTATION]

Apache HTTP Server Version 1.3

Module mod_mmap_static

This module provides mmap()ing of a statically configured list of frequently requested but not changed files.

Status: Experimental
Source File: mod_mmap_static.c
Module Identifier: mmap_static_module
Compatibility: Available in Apache 1.3 and later.

Summary

This is an experimental module and should be used with care. You can easily create a broken site using this module, read this document carefully. mod_mmap_static maps a list of statically configured files (via MMapFile directives in the main server configuration) into memory through the system call mmap(). This system call is available on most modern Unix derivates, but not on all. There are sometimes system-specific limits on the size and number of files that can be mmap()d, experimentation is probably the easiest way to find out.

This mmap()ing is done once at server start or restart, only. So whenever one of the mapped files changes on the filesystem you have to restart the server by at least sending it a HUP or USR1 signal (see the Stopping and Restarting documentation). To reiterate that point: if the files are modified in place without restarting the server you may end up serving requests that are completely bogus. You should update files by unlinking the old copy and putting a new copy in place. Most tools such as rdist and mv do this. The reason why this modules doesn't take care of changes to the files is that this check would need an extra stat() every time which is a waste and against the intent of I/O reduction.

Directives

MMapFile directive

Syntax: MMapFile filename [filename] ...
Default: None
Context: server-config
Override: Not applicable
Status: Experimental
Module: mod_mmap_static
Compatibility: Only available in Apache 1.3 or later

The MMapFile directive maps one or more files (given as whitespace separated arguments) into memory at server startup time. They are automatically unmapped on a server shutdown. When the files have changed on the filesystem at least a HUP or USR1 signal should be send to the server to re-mmap them.

Be careful with the filename arguments: They have to literally match the filesystem path Apache's URL-to-filename translation handlers create. We cannot compare inodes or other stuff to match paths through symbolic links etc. because that again would cost extra stat() system calls which is not acceptable. This module may or may not work with filenames rewritten by mod_alias or mod_rewrite... it is an experiment after all.

Notice: You cannot use this for speeding up CGI programs or other files which are served by special content handlers. It can only be used for regular files which are usually served by the Apache core content handler.

Example: 
  MMapFile /usr/local/apache/htdocs/index.html

Note: don't bother asking for a for a MMapDir directive which recursively maps all the files in a directory. Use Unix the way it was meant to be used. For example, see the Include directive, and consider this command:

  find /www/htdocs -type f -print \
  | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf

Apache HTTP Server Version 1.3

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