Wikimedia Bugzilla is closed!

For en wikipedia and all non-big wikis at Wikimedia I've 
done "alter table cur drop index cur_namespace". This index 
was too often being used for queries like 
Parser:replaceLinkHolders, the 500 article allpages subpages 
and other things where namespace_title should be used. The 
rest of the wikis will be changed during off peak read only 
time.

If not already done, I recommend that this index be removed 
from all MediaWiki installations by the installer. May 
already have been done - I recall past discussion of this.