Worker reads outdated data from db

[Chris Kopsidas]

Hello,

I create a worker from a callback which is triggered when a specific field of my model is set to true. The worker starts as expected.

It performs its task and continually checks if this field is true or false. Based on this field value it continues its task (if it is true) or exits (if it is false).

But even when this field for the monitored object is changed on db (I validate this via psql cmd line) the worker still reads the old value! It never reads the new value no matter how much time passes, so it never exits. Is this a caching issue? Something else?

[Mike Perham]

Do you see the same behavior in Rails console?

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[Chris Kopsidas]

In rails console the specific entry is also false, as it should be. I use "after_save" call back to trigger the worker, the same issue appeared also with "before_save". The worker is triggered using "perform_async". It is like the worker has its own db snapshot :|

Does sidekiq use any caching or other mechanism that might be blocking it reading from disk? Maybe any related configuration?

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[Mike Perham]

Could you try after_commit instead of after_save?  It’s possible Sidekiq is checking the database before the transaction has committed.

https://github.com/mperham/sidekiq/wiki/FAQ#why-am-i-seeing-a-lot-of-cant-find-modelname-with-id12345-errors-with-sidekiq

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[Chris Kopsidas]

I did the change and restarted both sidekiq and rails server. Unfortunately same behavior with this callback too.

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[Mike Perham]

Do you see the same behavior if you make the change in one Rails console and read in another Rails console?

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[Chris Kopsidas]

No, when I save the object I can immediately see the change in the second rails console which was already spawned.. Sidekiq worker does not get the new value when the change is done via console too. I don't know if it somehow affects the framework behavior but I am using rail_admin to perform the changes. But I only face this issue concerning sidekiq worker, everything else seems to be updated normally.

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[Mike Perham]

I can’t explain that then.  Part of Sidekiq’s ethos is that it never touches your database or any ActiveRecord code at all.  It boots Rails and uses the ActiveSupport::Executor API to run your job code, that’s it.

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[Chris Kopsidas]

Hmm, ok, thank you for your time and support. So there is not a scenario where sidekiq gets the model as is in memory and accesses this instead of the disk?

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[Mike Perham]

Sidekiq doesn’t do anything but execute your perform method.  It has no idea how your Rails app and ActiveRecord are configured, esp wrt caching.

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[Chris Kopsidas]

Thank you again! I will try to debug it, I will come up with something hopefully.

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[jo...@symdistro.com]

Hey Chris, did you get this worked out? The wiki's trouble shooting page suggests using more precise caching with config.active_record.cache_timestamp_format = :nsec.

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[Chris Kopsidas]

Hello,

Thanks for the interest. We decided to implement a completely different approach for our service so we did not have to use this mechanism at all.

[Phan Anh Le]

One of the potential culprits is that if the check is a loop within an open transaction then it might not see the update if the isolation level is repeatable-read.