In MediaWiki 1.18, when you set DBA as the main caching mechanism ($wgMainCacheType = CACHE_DB) you'll run into an error.

In includes/objectcache/DBABagOStuff.php on line 17 you check if $dir === false or not. In my case it isn't, so you assign its value to $this->mFile = "$dir/mw-cache-" . wfWikiID();.

The problem is that from v1.18 on the $dir is an array.

I got the following when I print_r'd the $dir variable in the first line of the __construct function: Array ( [class] => DBABagOStuff ).

Of course in this case the $this->mFile = "$dir/mw-cache-" . wfWikiID(); line will be broken also and that's why later MW cannot open the DBA cache.

For an ugly workaround I forced the $wgTempDirectory to be assigned to the $dir variable:

if ( $dir === false || is_array($dir) ) {
global $wgTmpDirectory;
$dir = $wgTmpDirectory;
}

Version: 1.18.x
Severity: major