mahara-contributors team mailing list archive

[Robert Lyon <robertl@xxxxxxxxxxxxxxx>]

Here is some good information on how to avoid deadlocks in mysql:
http://dev.mysql.com/doc/refman/5.0/en/innodb-deadlocks.html

One of the more interesting points is
* Always be prepared to re-issue a transaction if it fails due to deadlock. Deadlocks are not dangerous. Just try again

And at http://stackoverflow.com/questions/2596005/working-around-mysql-error-deadlock-found-when-trying-to-get-lock-try-restarti it mentions
 "Often you can just put a try/catch around the query execution logic and look for a deadlock when errors occur. If you catch one, the normal thing to do is just attempt to execute the failed query again."

So we could try that for a start

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https://bugs.launchpad.net/bugs/1492919

Title:
  Deadlock issues when 20-30 users copying collections & pages at the
  same time

Status in Mahara:
  Triaged

Bug description:
  Multiple users on the forum have reported deadlock issues when there
  are many users (20-30) copying pages & collections at the same time.
  See
  https://mahara.org/interaction/forum/topic.php?id=7309&offset=0&limit=10

  Note that 20 to 30 users is around the number you'd hit if you're
  running a whole class of users through a training session at the same
  time.

  The three reported cases of this are all in 15.04, so it may be a
  problem introduced in that version.

  The problem has been reported in both Postgres & MySQL.

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