Lighttpd

= CML aka Cache Meta Language =

What Is It

CML tries to move the decision about a cache-hit and cache-miss for a dynamic website
out of the dynamic application, removing the need to start the application or dynamic
language at all.

Especially PHP is know to have a huge overhead before the script is started to be executed.

How To Install

The language used by CML is LUA which you can find at http://www.lua.org/

The get some background how to write LUA check out:

• http://lua-users.org/wiki/LuaAddons
• http://luaforge.net/

Benifits

The main benifit of CML is its performance.

A very simple benchmark showed:

• about 1000 req/s for the static 'output.html' which is generated
• about 600 req/s if index.cml is called (cache-hit)
• about 50 req/s if index.php is called (cache-miss)

Using CML improves the performance for the tested page by a factor of 12, getting
near enough to the possible maximum of the static file transfer.

Usage Patterns

http://www.lighttpd.net/ is using CML to reduce the load (even if the load is minimal).

The layout of the front page depends on a few files:

• content-1
• content-6
• the template /main.tmpl

If one of the files gets changed the cached version of the page has to be changed too.

{{{
output_contenttype = "text/html"

trigger_handler = "index.php"

-- this file updated by the trigger
output_include = { "output.html" }

docroot = request["DOCUMENT_ROOT"]
cwd = request["CWD"]

-- the dependencies
files = { cwd .. "content-1", cwd .. "content-6", docroot .. "main.tmpl" }

cached_mtime = file_mtime(cwd .. "output.html")

-- if one of the source files is newer than the generated files
-- call the trigger
for i,v in ipairs(files) do
if file_mtime(v) > cached_mtime then return 1 end
end

return 0
}}}

CML and Databases

CML doesn't provide direct access to databases like MySQL or PostgreSQL. And to make sure that we don't get the request later: It will never get it.

There is a better/faster way to interface CML with Databases: [http://www.danga.com/memcached/ memcached(8)]

All you have to do is keeping the interesting information to decide if a page has to regenerated in a memcached storage. Let's say what whenever you store a entry in the database you associate a Version-ID with it. The Version-ID is incremented as soon as you make a change to the resource.

This version Version-ID is now stored in the Database and in memcache at the same time. CML can now fetch the Version-ID, check if content has been generated for it, generate it if necessary.

{{{
output_contenttype = "text/html"

key = md5(request["PATH_INFO"])
version = memcache_get_long(key)
cwd = request["CWD"]

trigger_handler = "generate.php"

if version >= 0 then
output_include = { cwd .. key .. "-" .. version .. ".html" }
return 0
else
return 1
end
}}}

generate.php will have to:

• get PATH_INFO
• fetch information from database about it
• generate content for the page and write it to disk
• deliver it to the client

To interface the database with the memcached you can use a UDF:

• for MySQL can get the mysql udf at [http://jan.kneschke.de/projects/mysql/udf/ jans mysql page]
• for PostgreSQL Sean Chittenden has written [http://people.freebsd.org/~seanc/pgmemcache/ pgmemcache]

In MySQL you do: :: {{{
SELECT memcache_set("127.0.0.1:11211", "123", "12");
}}}
or to retrieve a value: :: {{{
SELECT memcache_get("127.0.0.1:11211", "123");
}}}