Apache module mod_mmap_static
This module provides mmap()ing of a statically configured list of frequently requested but not changed files.
Source File: mod_mmap_static.c
Module Identifier: mmap_static_module
Compatibility: Available in Apache 1.3 and later.
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
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.
Syntax: MMapFile filename [filename] …
Override: Not applicable
Compatibility: Only available in Apache 1.3 or later
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_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.
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