The English-language Wikipedia will be in _read-only mode_ for a few hours tonight (Feb 9->Feb 10) while the database structure is altered to eliminate some of the remaining performance drags before the heavy weekday traffic gets into full swing.
This will also fix the out-of-order page history bug, which was caused by a temporary workaround to the slow history problem.
The downtime window will cover roughly 04:00-08:00 UTC (UK time). For us USians, that's 8pm-midnight PST / 11pm-3am EST. Australians & others, please check http://www.wikipedia.org/wiki/Time_zone for the appropriate offset to your local time. (I'm not certain of the end time; it may run shorter, and hopefully won't run longer. It's a big database, and mass modifications take a *long* time.)
During that time the wiki should remain accessible for reading, but no one will be able to log in or make edits.
I'll also be upgrading various other languages to the current software revision; those should go relatively quickly, and will be staggered. Generally, meta, wiktionary, and Wikipedia's other languages should remain accessible for both reading and editing through the night except for some brief read-only outages.
-- brion vibber (brion @ pobox.com)
ps Tech note: I figure we should hold off on the mysql 4 upgrade until they can release a version that isn't followed within a day by a dire warning about a new bug that directly affects a type of query that we use a lot for Wikipedia. :)
In the meantime, I'm adding the inverse timestamp column which can be sorted on the index by mysql 3 (thus speeding and fixing bugs in history, contribs, & recentchangeslinked), and a random queue index column to replace the separate table and its insanely slow refilling operation.