Update: There is be a new version of this module. Click here to get it.
I created a module that generates XML Sitemaps for Pligg ( the well known open source cms used for creating sites similar to digg.com ).
The module generates a sitemap index and sitemaps with all the stories in the database dynamically so nothing is stored on disk and you don't have to set a cron job to generate it.
The sitemaps are updated automatically when a new story is submitted. Because of the structure of the sitemap index and because it contains "lastmod" info, the search engines should only download the latest entries in the index so you shouldn't worry about the module putting too much load on your system.
There is also a "ping" function that will announce google, yahoo and ask.com every time a new story is submitted so that they know they have to download the sitemap. The ping function required a little patching to pligg source code to add some hooks ( only if you use 9.6, 9.7 should already have those hooks ). Here is the diff file in case you use pligg 0.9.6 : pligg submit hooks diff
The module was only tested on pligg 0.9.6, I haven't upgraded to 0.9.7 yet, so if you try this on 0.9.7 let me know how it works, any feedback is appreciated.
You can download Xml_Sitemaps module from here: xml_sitemaps-0.1.tar.gz and in case you want to verify it here is the md5 sum and the sha256 sum
the code is released under the same license as pligg, so feel free to use it, modify and share.
This is pretty straight forward, you have to install this like any other pligg module, just put the .tar.gz file in the modules, un-archive it then go into pligg admin and activate it. If you use pligg 0.9.6 and you want to be able to ping the search engines don't forget to apply the submit hooks patch .
After installation you should be able to access the sitemap index like this : http://yourdomain.com/module.php?module=xml_sitemaps_show_sitemap or if you want the sitemap to look friendly ( btw ask.com will only accept a friendly sitemap ending in .xml ) , you just have to go into Admin->Configuration->XmlSitemaps and enable "Sitemap Friendly URL", and if you do that then you have to put the following lines in your .htaccess somewhere before the line "##### URL Method 2 ("Clean" URLs) Begin #####" :
RewriteRule ^sitemapindex.xml module.php?module=xml_sitemaps_show_sitemap [L]
RewriteRule ^sitemap-([a-zA-Z0-9]+).xml module.php?module=xml_sitemaps_show_sitemap&i=$1 [L]
Here is how the index looks on a site with sitemap friendly urls enabled: http://sapa.ro/sitemapindex.xml
There are other configuration options in there, you can set the maximum number of stories to put in a sitemap, and you can chose whether to ping any of the three search engines supported. You can also set your yahoo.com key in there if you want to ping yahoo.
That's it! Happy Sitemapping! and as always ... let me know how it works in the comments.