[jira] [Commented] (AIRFLOW-30) Make preoperators part of the same transaction as the actual operation

["Chris Riccomini (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/AIRFLOW-30?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15266837#comment-15266837 ] 

Chris Riccomini commented on AIRFLOW-30:
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Initially, this seemed fine to me, but it actually sounds a little tricky to me. The concern I have is what happens if the DAG fails half way through and the transaction is reverted? In such a case, Airflow will show prior operators as having successfully run, but their state mutation will not have taken place. This effectively means that the entire DAG needs to be re-run, even if some of the operators show a successfully executed view.


> Make preoperators part of the same transaction as the actual operation
> ----------------------------------------------------------------------
>
>                 Key: AIRFLOW-30
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-30
>             Project: Apache Airflow
>          Issue Type: Improvement
>            Reporter: Bence Nagy
>
> All my use cases would work better if each operator would execute everything in one transaction. Two examples:
> - I want to {{GenericTransfer}} a set of rows from one DB to another, and I have to create the table first in the destination DB. I feel like it'd be a lot more clean if I didn't have empty tables lying around if the insertion fails for some reason later on.
> - I want to {{GenericTransfer}} all rows from an entire table periodically to sync it from one DB to another. To do this correctly I want to clear the destination table first to make sure I end up with no duplicate rows, so I'd have a {{DELETE * FROM dst_table}} preoperator. If the insertions fail afterwards, I'd end up with no data (it would be better in most cases to fall back to the old data), and even if everything is working correctly, I'll have an empty table while the insertions as still executing.
> To fix this, the relevant {{DbApiHook}} methods could support a new kwarg to set whether it should commit at the end.
> Thoughts?



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