Last modified: 2011-07-24 10:41:59 UTC
When $wgMainCacheType is set to CACHE_DBA, in includes/BagOStuff.php, on line 672 MediaWiki uses $wgTmpDirectory instead of $wgCacheDirectory. $wgCacheDirectory is allowed to be "false", in which case it disables local caching: "Directory for caching data in the local filesystem. Should not be accessible from the web. Set this to false to not use any local caches."
For later references, the file in 1.17.0 is: http://svn.wikimedia.org/viewvc/mediawiki/tags/REL1_17_0/phase3/includes/BagOStuff.php?revision=90570&view=markup The code being referred too is in DBABagOStuff::__construct()