Rob Church and Timwi wrote (regarding frequency of edits that change
categories):
Probably higher than that, to be honest, especially with all those
Wikipedians running around, dealing with Special:Uncategorisedpages,
and correcting stub templates and so forth.
Also don't forget about vandals just blanking a (categorised) page, plus
the immediately following revert.
Okay, well, so that we have some quantified data and can think make a firm
decision one way or the other about the suitability of a MyISAM table for
category intersections, I'll take a random sample of edits (of some
statistically significant size - doesn't take much) and see how many involve
a category change and report back.
And, as always, anybody else got any ideas? If this can't work, I can't
think of anything else beside a separate Lucene index (which will then not
be real time and have to be updated every so often) as I don't think
excluding large categories from an intersection search is an acceptable
solution.
Thanks,
Aerik