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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
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
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