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CML (Cache Meta Language)
Module: mod_cml
:Author: Jan Kneschke
:Date: $Date: 2004/11/03 22:26:05 $
:Revision: $Revision: 1.2 $
CML is a Meta language to describe the dependencies of a page at one side and building a page from its fragments on the other side using LUA.
.. meta::
:keywords: lighttpd, cml, lua
.. contents:: Table of Contents
CML (Cache Meta Language) wants to solves several problems:
* dynamic content needs caching to perform
* checking if the content is dirty inside of the application is usually more expensive than sending out the cached data
* a dynamic page is usually fragmented and the fragments have different livetimes
* the different fragements can be cached independently
Cache Decision
A simple example should show how to a content caching the very simple way in PHP. has a very simple design:
* the layout is taken from a template in templates/jk.tmpl
* the menu is generated from a menu.csv file
* the content is coming from files on the local directory named content-1, content-2 and so on
The page content is static as long non of the those tree items changes. A change in the layout
is affecting all pages, a change of menu.csv too, a change of content-x file only affects the
cached page itself.
If we model this in PHP we get: ::
## ... fetch all content-* files into $content
$cachefile = "/cache/dir/to/cached-content";
function is_cachable($content, $cachefile) {
if (!file_exists($cachefile)) {
return 0;
} else {
$cachemtime = filemtime($cachefile);
foreach($content as $k => $v) {
if (isset($v["file"]) &&
filemtime($v["file"]) > $cachemtime) {
return 0;
if (filemtime("/menu/menu.csv") > $cachemtime) {
return 0;
if (filemtime("/templates/jk.tmpl") > $cachemtime) {
return 0;
if (is_cachable(...), $cachefile) {
} else {
# generate content and write it to $cachefile
Quite simple. No magic involved. If the one of the files is new than the cached
content, the content is dirty and has to be regenerated.
Now let take a look at the numbers:
* 150 req/s for a Cache-Hit
* 100 req/s for a Cache-Miss
As you can see the increase is not as good as it could be. The main reason as the overhead
of the PHP interpreter to start up (a byte-code cache has been used here).
Moving these decisions out of the PHP script into a server module will remove the need
to start PHP for a cache-hit.
To transform this example into a CML you need 'index.cml' in the list of indexfiles
and the following index.cml file: ::
output_contenttype = "text/html"
b = request["DOCUMENT_ROOT"]
cwd = request["CWD"]
output_include = { b .. "_cache.html" }
trigger_handler = "index.php"
if file_mtime(b .. "../lib/php/menu.csv") > file_mtime(cwd .. "_cache.html") or
file_mtime(b .. "templates/jk.tmpl") > file.mtime(cwd .. "_cache.html")
file.mtime(b .. "content.html") > file.mtime(cwd .. "_cache.html") then
return 1
return 0
Numbers again:
* 4900 req/s for Cache-Hit
* 100 req/s for Cache-Miss
Content Assembling
Sometimes the different fragment are already generated externally. You have to cat them together: ::
We we can do the same several times faster directly in the webserver.
Don't forget: Webserver are built to send out static content, that is what they can do best.
The index.cml for this looks like: ::
output_content_type = "text/html"
cwd = request["CWD"]
output_include = { cwd .. "head.html",
cwd .. "menu.html",
cwd .. "spacer.html",
cwd .. "db-content.html",
cwd .. "spacer2.html",
cwd .. "news.html",
cwd .. "footer.html" }
return 0
Now we get about 10000 req/s instead of 600 req/s.
You need `lua <>`_ and should install `libmemcache-1.3.x <>`_ and have to configure lighttpd with: ::
./configure ... --with-lua --with-memcache
To use the plugin you have to load it: ::
server.modules = ( ..., "mod_cml", ... )
the file extension that is bound to the cml-module
hosts for the memcache.* functions
(not used yet)
The language used for CML is provided by `LUA <>`_.
Additionally to the functions provided by lua mod_cml provides: ::
- parameters from the query-string
string md5(string)
number file_mtime(string)
string memcache_get_string(string)
number memcache_get_long(string)
boolean memcache_exists(string)
What ever your script does, it has to return either 0 or 1 for ``cache-hit`` or ``cache-miss``.
It case a error occures check the error-log, the user will get a error 500. If you don't like
the standard error-page use ``server.errorfile-prefix``.