Good evening,

I am currently starting with my diploma thesis at the Semantic Mediawiki group at University Karlsruhe. I will investigate caching issues in this context and therefore I started with looking at Mediawiki / Wikipedia caching and database updates.

From what I got from the documentation there are three types of caches:

1) Squid HTTP caches (invalidated via Multicast HTCP purging). These caches rewrite HTTP-header for client caching if necessary. If I got that right, the caching time depends on $wgSquidMaxage, and the client cache is invalidated once the user logs in or the page is edited. Now is the Wikipedia setting for $wgSquidMaxage equal to the default value given in the documentation (18000)? And is this caching strategy enforced only in sendCacheControl() or are there other functions I have to look at? 2) The parser cache which temporarily keeps already parsed pages - this cache is either in memory or in a special table(?). 3) Some memory cache named memcached that is able to cache database queries and distribute writes across the database architecture. This is similar to MySQL query caching?

Another issue are database updates (these occur only, if I edit and change a page, right? (assuming parser cache is enabled)) - what influence does caching have on these? I have to admit that I have not dived deep enough into the code to understand where and how these updates happen.

I know that is a bunch of question, yet I appreciate any help, be it answers or links to documentation I have not looked at, yet, very much.

Thanks in advance, Sebastian