Caching frequently requested files that change very infrequently is a technique for reducing server load. mod_file_cache provides two techniques for caching frequently requested static files. Through configuration directives, you can direct mod_file_cache to either open then mmap()a file, or to pre-open a file and save the file's open file handle. Both techniques reduce server load when processing requests for these files by doing part of the work (specifically, the file I/O) for serving the file when the server is started rather than during each request.
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.
This module is an extension of and borrows heavily from the mod_mmap_static module in Apache 1.3.
Not all platforms support both directives. For example, Apache
on Windows does not currently support the
The 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 (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.
The
Insert more details about sendfile API...
This file handle caching is done once at server start or
restart, only. So whenever one of the cached files changes on
the filesystem you have to restart the server (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
Be careful with the file-path 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
The
Be careful with the file-path 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