[jira] [Created] (HIVE-11833) TxnHandler heartbeat txn doesn't need to serializable DB txn level

["Sergey Shelukhin (JIRA)" <ji...@apache.org>]

Sergey Shelukhin created HIVE-11833:
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             Summary: TxnHandler heartbeat txn doesn't need to serializable DB txn level
                 Key: HIVE-11833
                 URL: https://issues.apache.org/jira/browse/HIVE-11833
             Project: Hive
          Issue Type: Bug
            Reporter: Sergey Shelukhin
            Assignee: Sergey Shelukhin


What it does is:
1) Blindly update lock heartbeat time, fails if not found.
2) Get txn state.
3) If not found, look for txn in completed, fails regardless of result.
4) Update txn heartbeat time if not (3) and not aborted.

All this can run the same under repeatable-reads.
Now if it runs under read-committed, someone could 
1) update txn state after we read it
2) delete txn state (moving to completed) after we read it
3) same for completed state
In case of 1 we will update heartbeat for e.g. aborted txn without detecting it.
In case of 2 the update will produce 0 rows so we will detect that and can check completed as we already do.
The 3 case seems like it doesn't matter.

I don't know if (1) matters. These heartbeats happen often and can cause contention on the db




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