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Forums Using DNN Platform Performance and Optimization

Scheduler suddenly stops working

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Gus
New Around Here
Posts: 3
New Around Here
3/1/2024 2:28 PM

    We're using DNN v. 09.12.00 (0) and since we upgraded to this version, we've noticed that the scheduler suddenly stops working and no scheduled tasks get executed and when trying to manualle run the scheduled task, nothing happens (no visual error is displayed), no task gets executed. Reviewing the logs we can see the following error after attempting to manually run a scheduled task:

    2024-02-27 23:57:57,210 [servername][Thread:Scheduler Thread][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidOperationException: Sequence contains no elements
       at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
       at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.ValidateServersAreActiveForScheduledItem(ScheduleItem scheduleItem)
       at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.AddToScheduleQueue(ScheduleHistoryItem scheduleHistoryItem)
       at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.LoadQueueFromTimer()
       at DotNetNuke.Services.Scheduling.Scheduler.CoreScheduler.Start()

    This is a strange error, as all Scheduled Tasks had been running fine until an unlown point when suddenly it stops working. Looking into the  ValidateServersAreActiveForScheduledItem method, the code shouldn't even be reaching that point as there is no server name attached to the Scheduled Task, it is blank, so the ValidateServersAreActiveForScheduledItem should return true all the time.

    This issue gets resolved by restarting the app and then everything starts working again. Wondering if anyone out there has seen this issue or something similar?

    Gus

    2
    Will Strohl
    Senior Member
    Posts: 1362
    Senior Member
    3/1/2024 4:04 PM

      First, hopefully, you're not experiencing issues due to changes to the core of DNN. I'd recommend using the Security Analyzer in the persona bar to see if there are any detectable issues.  

      Next, it's worth noting that the Scheduler is not running constantly, by default.  Sometimes when you go in, if there aren't any actively running tasks, it will appear to not be running.  What's your setting for the scheduler right now? 

      Also, it's not completely unusual to have intermittent or even regularly occurring errors resulting from the scheduler.  Most often, this is either due to orphaned scheduled tasks that should be removed/disabled; and from the servers table having invalid server names. 

      Be sure to look at the Servers view in the persona bar and use the "Remove Inactive Servers" feature, if it's there.  

      Next, review all of the scheduled tasks to see if any are actually no longer necessary. 

      Gus
      New Around Here
      Posts: 3
      New Around Here
      3/1/2024 4:16 PM

        Thank you for your reply Will! We're going over your suggestions and will post here our findings.

        Gus

        3
        Gus
        New Around Here
        Posts: 3
        New Around Here
        3/1/2024 4:16 PM

          Thank you for your reply Will! We're going over your suggestions and will post here our findings.

          Gus

          3
          Daniel Valadas
          Advanced Member
          Posts: 217
          Advanced Member
          3/1/2024 5:23 PM
            In any scheduled task details, check the "Server" field is empty. That field can be used to run that task only on a specific server and if that server no longer exists, it might be your issue.
            3
            James Clarkson
            Growing Member
            Posts: 78
            Growing Member
            3/1/2024 6:54 PM
              In Persona Bar -> Settings -> Servers -> System Info -> WEB SERVERS, check that all of the servers listed there exist and are contactable. Remove anything that is out of date.
              3

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