Revision as of 19:00, 26 July 2008

Hello, my name is EmuWikiAdmin1, and I realised lately that my website will need DPL to cache its output if I want to have high traffic and not overload the server with too many DPL requests. I thus decided to start this page here and start modifying the DPL code so we have a caching system for DPL. Eventually this code could be included in the official DPL releases if that's what Gero wants, or we can just keep it separated and used only by those who really need it, it will be the decision of Gero.

What's been done

• A table named dplcache is added to the mediawiki database following DPL installation. (if not already created)

• A new parameter is added to DPL : |CacheID=. User can either specify a 6 number (ex : 924924) cache ID, or he can just put CacheID=true. In the case where the user specifies a cache ID, DPL tries to find the cached content associated with this ID. The advantage is, for example, if you have multiple pages with the same DPL invocations, you could just give them the same cacheID, thus preventing from having to maintain multiple caches that would actually contain the same thing. In case the paramater is CacheID=true, then DPL chooses a random available cache ID and actually replaces the CacheID=true string with CacheID=xxxxxx in the wikitext.

• The render function of the DPL parser function is modified : before rendering, check if the CacheID parameter is used. If it is used, then don't refresh the DPL content : just output the cache content from the database. In case the CacheID parameter is present but the database does not have cache content for this cacheID, then just refresh the DPL, store it in the cache, and display the refreshed content to the user. So basically, how the cache works is that it always look for the content in the database, if it's not there, it creates it. So our expiration system will be very simple : just delete the field values associated with a cacheID in the database if we want it to expire. The next time a user goes to a page with the DPL invocation, it will get refreshed.

What's left

• Special page that would allow the administrators to empty all the DPL cache

• Rules for expiration of contents (category-related changes in articles, changes of templates used in the DPL invocation, changes in articles called by the DPL invocation). I need your help on this one Gero : I would like to put a ArticleSave or ArticleSaveComplete hook to detect if there were any change in categories. I got the wikitext but I don't know how to render it to know the final output (expand templates, generate the DPL result). I went to MediaWiki_extensions_FAQ - how to render wikitext but they don't give examples with ArticleSave and it seems that ArticleSave hook functions do not receive the &$parser parameter, which we need to use functions like parse() or recursiveTagParse(). Do you know how we could guess the final output of the text from the ArticleSave hook ?

• Maybe a user-controllable bouton that would make the content of the cache expire.

Discussion

Add your input here.

Code

This is the current state of the code. Improvments are welcome. If you want to see only the differences from the original DPL code, search for //EmuWikiAdmin. This is alpha-quality code. Do not use on a production server. :

cachecode.txt

Note

Gresat that you started this!

1. check if the MW12 hack ("parser must be coaxed ..") is really needed. I think you can just return the cached content. Yep, really needed on 1.12. Actually the output seems ok, except if your DPL invocation you call a parser function, then the parser functions refuses to output.
2. Please use a new revision number, I recommend 1.8.0 Done
3. I don´t think the ArticleSave hook will do the job. Try ParserAfterTidy or something similar. You must get access to the parser and you need access to data structures which tell you to which categories the article being edited belongs.
4. you must also catch the "delete article" operation.

Good luck!

Gero 18:44, 26 July 2008 (CEST)