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Fixed Crons stopped running

Discussion in 'Resolved Bug Reports' started by digitalpoint, Sep 14, 2013.

  1. digitalpoint

    digitalpoint Well-Known Member

    Under 1.2.0, my crons would stop every couple days (mainly because of some Twitter API stuff I was doing and when the Twitter API failed, it would cause an error while running the cron).

    This was fixed in 1.2.1, but I still ran into an issue where the cron tasks just stopped working again (only has happened once).

    I did some checking around in the code, and I suspect it's the
    XenForo_Model_Cron::getMinimumNextRunTime() method that can cause crons to stop working every once in a blue moon.

    If the query it runs fails for whatever reason, cron will effectively stop running (maybe there's a locking issue and the query times out... maybe you are in the middle of restarting MySQL so it went away for a split second while that query ran, etc.)

    If that query returns nothing, the system sets the next cron run time to January 19, 2038.

    In theory that cron should *never* return nothing unless all crons are disabled.

    It probably would be a better idea to fall back to a default next run time of something more reasonable... like 15 minutes in the future, rather than never checking again for crons to run until 2038.
     
    mjda, sonnb, erich37 and 7 others like this.
  2. Mike

    Mike XenForo Developer Staff Member

    The fallback is probably reasonable, but I think it's very unlikely that is the cause -- it's likely still a potential race condition that's wiping out the deferred process. I have already tweaked this again for 1.2.2 as I realized that there was a situation where a fatal error could still trigger a problem, particularly on a busy site. I think that fits you... ;)

    If it happens again, before you fix it, look at your xf_deferred table. If you don't see a "Cron" entry, then you got hit by the race condition.
     
    Adam Howard, digitalpoint and Chris D like this.
  3. digitalpoint

    digitalpoint Well-Known Member

    Not sure what the race condition that was tweaked in 1.2.2 was, but would it apply to a setup that the deferred.php only runs once a minute? We removed the system that triggers it from page views and instead trigger deferred.php every minute from a single server via crontab.

    Code:
    * * * * *       root    /usr/local/bin/php /home/sites/digitalpoint.com/web/deferred.php > /dev/null 2>&1
     
    shenmuee likes this.
  4. digitalpoint

    digitalpoint Well-Known Member

    Haven't upgraded to 1.2.2 yet, but happened again today. The xf_deferred table has no records in it... so I hopefully it's whatever was fixed in 1.2.2. There also wasn't a MailQueue entry in there until we disabled/reenabled a random cron.
     

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