2009/9/2 Ilmari Karonen nospam@vyznev.net:
(Although Roan's suggestion of also folding things like {{CURRENTYEAR}} and passing their expiration time to the cache may also be worth considering. We could then just treat e.g. {{SITENAME}} as having an infinite expiration time, and any truly uncacheable magic words as expiring immediately.)
When using CDB, the cache is constant. You can't do incremental updates. And what if WMF uses *single* cache for all projects? Then {{SITENAME}} wouldn't be constant anymore, and we would not get better performance where it is needed most. It could help other MediaWiki installations a bit, just how much... I don't know.