ts4294967296 at hotmail
Nov 22, 2003, 12:56 AM
Post #4 of 4
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Evan wrote:
> >>>>> "BV" == Brion Vibber <brion [at] pobox> 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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wikipedia.cvs20031121.with-cookie-check.diff
