I've implemented a "maxlag" parameter to index.php which can be used by bots to voluntarily throttle their write rate and mitigate slave lag on the server.
http://www.mediawiki.org/wiki/Maxlag_parameter
It came out of the discussion here:
http://en.wikipedia.org/wiki/Wikipedia:Bot_owners%27_noticeboard#Maxlag_para... Permalink: http://en.wikipedia.org/w/index.php?title=Wikipedia:Bot_owners%27_noticeboar...
-- Tim Starling