Evan wrote:
"BV" == Brion Vibber brion@pobox.com writes:
Me> OK, so, I took my first crack at working on MediaWiki with an Me> attempt to check for cookies when logging in (bug #770011). BV> Great! I'm in the middle of the SoCal Linux Expo and will look BV> this stuff over when I get a chance... If some of the other BV> developers could look after this that'd be great.
I might have a quick look now.
Coolio! The patches I submitted are all independent -- none depends on another, that I can see, nor should they conflict -- and made against the HEAD for phase3. Some use global variables, so I'm going to wait till they're applied (or rejected B-) before trying to jigger with the $REQUEST hoohaw.
I'm going to try and cut my teeth on the transactions stuff. I figure I'll just try to find calls to wfQuery() with INSERT, UPDATE, DELETE in them, and wrap something like wfBegin()/wfCommit() around them, with wfRollback() for error conditions.
I'll probably miss 20% of them, and screw everything up. Should be a fun time.
Missing 20% is a lot better than missing 100%, which is what we're doing at the moment. It's really making a mess of our database, we often have to clean up inconsistencies manually. So everyone will be eternally grateful.
But before you start, I have to make sure you know about the dangers of transactions. These dangers were discussed by Brion and I on wikitech-l, in mid-August 2003 under the subject "Using HEAP tables":
http://mail.wikipedia.org/pipermail/wikitech-l/2003-August/thread.html
Transactions have to be guarded against user aborts. This could be done either with a "critical section" model, where user aborts are disabled for the duration of the transaction, or alternatively a shutdown function could be used. The shutdown function would rollback any active transactions. However note that installing a shutdown function effectively disables user aborts anyway. When there is a shutdown function, PHP only checks for pending user aborts on output -- in our case, once per run.
If a PHP thread dies while a transaction is active, any locked tables will remain locked indefinitely. The wiki will effectively become read-only until a developer manually flushes the lock. We've seen this happen on the English Wikipedia.
AFAIK, killing threads by restarting the webserver doesn't pose a risk, because the MySQL connections will also be terminated, releasing any lock.
More information about user aborts is at: http://www.php.net/manual/en/features.connection-handling.php
This discussion, and patch submissions, are probably more on-topic at wikitech-l than at mediawiki-l. This post (and a couple of Brion's) have been cross-posted there.
-- Tim Starling
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