Cron task gets triggered too often if one-off task is run

[helloagain-dev]

I have a daily task that runs at 08:00 which takes can take up to 20 minutes to complete.
I also have one-off tasks that run at different times.
I noticed a scenario where my daily task which should only run once per day ran 3 times. In this case a one-off task was also scheduled for 08:00.

A test-scenario that reproduced this issue (from time to time was the following):

• Have a long-running task (just sleep for 120 seconds) LT that is executed every hour as a cronschedule (0 * * * *)
• Have a short task (just log something) ST that can be scheduled at arbitrary times. This is a periodic task with an interval set to 1 minute and has the scheduled start_time with one_off=True
• All of them are in timezone Europe/Vienna

Schedule the following:

• 07:59: ST
• 08:00: LT
• 08:00: ST
• 08:01: ST

This leads to the LT being executed more than once sometimes.
I believe it has something to do with the schedule being changed and the last_run_at time not being written yet.
At least I get the following messages after the ST ran:

E  [2019-02-07 08:00:16,197: INFO/Beat] DatabaseScheduler: Schedule changed.
E  [2019-02-07 08:00:16,197: INFO/Beat] Writing entries...
E  [2019-02-07 08:00:16,576: INFO/Beat] DatabaseScheduler: Schedule changed.
E  [2019-02-07 08:00:16,576: INFO/Beat] Writing entries...
E  [2019-02-07 08:00:17,284: INFO/Beat] DatabaseScheduler: Schedule changed.
E  [2019-02-07 08:00:17,284: INFO/Beat] Writing entries...

Is this the intended behaviour? In other words does celery beat give a guarantee that the task is only run once or does it just mean it will run at least once and I have to check myself if it was already called.

It also seems to be a bug of django-celery-beat as the logs indicate that celery-beat sends the task to celery a second time.

Versions:

Django==2.0.6
celery==4.2.1
# Latest django-celery-beat master as this contains a needed fix
git+https://github.com/celery/django-celery-beat.git@75491bf3ae2d1cbc4811711faba659e3860957c1#egg=django-celery-beat

[helloagain-dev]

Is anybody else experiencing this?

[adikshirsagar]

yes, I am also facing same issue.
I also run same task at 4:00 and 17:40 but it run twice for 4:00 and 4:03 and run 17:40 one time.

[prafulbagai708]

Was anyone able to resolve this problem? We're facing a similar issue

[auvipy]

which versions are you using

[baijiangjie]

Try it.

#660