Thanks Russell. I'm completely new to JMeter, so having that test plan to start from should save me a lot of time!
Unfortunately I didn't think to check "show engine innodb status" after running that deadlock (because I figure I could tell from the PHP errors which query it had died on and that was enough). And since then I have dropped that database. I'll make sure to check the next time the problem happens, though. Or perhaps I'll turn on that innodb_print_all_deadlocks setting it mentions in the MySQL manual. >From reading what the MySQL manual has to say about deadlocks, it seems like our underlying problem in Mahara is that we're doing the entire collection copy operation inside of a transaction. And that copy operation may take a while, depending on how many pages and how much content is in the collection, the speed of the DB connection, and whether it requires copying files in dataroot as well. Just having a long-running transaction makes it a lot more likely that we'll hit deadlock problems. Although it's strange to me, because I have not heard of any deadlock problems with Mahara in Postgres. Instead, the site tends to just slow down under heavy usage. Although perhaps that's Postgres being willing to wait longer for the deadlock to clear? Once I'm able to replicate this with JMeter I'll explore some possible solutions. The most "brute-force" one would be to disable transactions entirely (maybe with a config-defaults.php option), if this actually is a problem caused by long-running transactions. -- You received this bug notification because you are a member of Mahara Contributors, which is subscribed to Mahara. Matching subscriptions: Subscription for all Mahara Contributors -- please ask on #mahara-dev or mahara.org forum before editing or unsubscribing it! https://bugs.launchpad.net/bugs/1514608 Title: MySQL deadlock issues with simultaneous users Status in Mahara: In Progress Bug description: The patch in Bug 1492919 resolved the deadlock issues for some users, but others are still reporting that they are getting deadlocks. This seems to be an issue unique to MySQL, and it can happen with as few as 2 or 3 concurrent users. It has been reported across all stable versions. Strangely, it seems to be a relatively recent issue (i.e. we never heard this with Mahara 1.8 or 1.7, etc), so this suggests it was triggered by something that changed fairly recently. One possible candidate is our switch to the mysqli driver (before that Mahara wasn't doing transactions at all, in mysql). See also: * https://mahara.org/interaction/forum/topic.php?id=7309 * https://mahara.org/interaction/forum/topic.php?id=7432 To manage notifications about this bug go to: https://bugs.launchpad.net/mahara/+bug/1514608/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~mahara-contributors Post to : [email protected] Unsubscribe : https://launchpad.net/~mahara-contributors More help : https://help.launchpad.net/ListHelp
