# prefect-community

Jessica Smith

06/10/2022, 12:52 PM
Curious if there is a best practice on something I'm struggling with. I have a task that creates a sql alchemy engine from a parameter, and this is passed on to the next set of tasks. However, you can't pickle a sql alchemy engine, which means I have checkpointing turned off for the Get Engine task. This means that if one of the queries fails and retries it will not have the input it needs. Do I need to just create the engine inside the task? Or is there another way people have used?
Is there a way I can have the GetEngine task marked to be re-ran before the query task retries?

Anna Geller

06/10/2022, 1:23 PM
I understand what you mean - it's considered best practice to define the sqlalchemy engine within a task, but you can also pass the connection string as a parameter value or as a Secret to downstream tasks

Kevin Kho

06/10/2022, 1:29 PM
You can’t retry an upstream task based on the result/state of a downstream task in 1.0

Jessica Smith

06/10/2022, 1:31 PM
Ah, I could replace the GetEngine task with a GetConnectionString task
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that would do the same thing and be pickleable
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thanks for the idea, i'll go with that!

Stéphan Taljaard

07/15/2022, 6:44 AM
Hey @Jessica Smith. I also had a similar use-case in the past. I wanted to do Prefect-
task runs on a list of len >100, each using the SQLAlchemy eninge. Though that can be flaky, if engine breaks, many mapped task run's can't auto-recover. Curious what are your thoughts on such a use-case?
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Jessica Smith

08/09/2022, 2:59 PM
Hey @Stéphan Taljaard, I think you sent this message right as I was switching jobs to a job that doesn't use Prefect. I'm back on the Slack now, but I doubt you still are looking for an answer for this. If you are, let me know, happy to give it some thought
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