PL/SQL Brain Teaser: when does a COMMIT not commit?

So your users make changes to tables (with great care and security, through your PL/SQL API), your app calls this procedure and that function. At some point along the way, a COMMIT statement is executed successfully in a user's session.

Yet that same user's session still has uncommitted changes!

Huh? How is this possible?

Think you know? Comment below!

Comments

  1. The commit was within an autonomous transaction.

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  2. commit write nowait/batch?

    ReplyDelete
  3. Autonomous Transaction :allows you to leave the context of the calling transaction, perform an independent transaction, and return to the calling transaction without affecting it's state.Hence the uncommitted changes in the users session are still significant.

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  4. Autonomous transaction! Love the brain teaser!!

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  5. Just few untested random use-cases in a hurry. Feel free to correct.
    1. Dirty data is in bulk collected collections. Processing commits in loop.
    2. View with instead of trigger. Trigger only uses partial data to update.
    3. Part of dirty data is written to a external table on really slow IO device.
    4. Distributed transaction. Part of dirty data has to be updated on some other DB.
    5. Call to external service from API with part of dirty data.
    6. Trigger on table allows selective data to update?

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  6. It all depends where in the process chain the commit was executed, if there were any dml statements after it, and if any rollback (to savepoint) was executed...

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  7. And here are some thoughts offered up on LinkedIn:

    * Is the commit statement outside the procedure? It so, it may be out of scope. Is there a rollback somewhere in the procedure or function?

    * The procedure having COMMIT might have executed with autonomously. So the user changes outside that procedure are still in process and not yet committed.

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  8. And now my answer: definitely, the answer in my mind is that the COMMIT statement was executed within an autonomous transaction subprogram.

    If you include

    PRAGMA AUTONOMOUS_TRANSACTION;

    in the declaration section of your procedure or function, then a COMMIT in that subprogram will commit only those changes made in the scope of that subprogram.

    Other outstanding changes in my session will NOT be committed.

    Now as to your comments:

    @stanley, I'd love to hear more explanation about some of your items, as they are outside my area of expertise. I am not sure if a distributed xaction applies here, since I reference the "user's session".

    @john, certainly any DML statements executed after the commit would be uncommitted. ROLLBACK TO before the commit would remove outstanding changes. After the commit? Well, the teaser has to do with state of session right after the commit (implied: before other actions take place).

    Thanks for participating!

    ReplyDelete

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