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

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

    [ https://issues.apache.org/jira/browse/HIVE-11833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14746359#comment-14746359 ] 

Sergey Shelukhin commented on HIVE-11833:
-----------------------------------------

[~alangates] [~ekoifman] can you take a look

> 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
>         Attachments: HIVE-11833.patch
>
>
> What it does is:
> 1) 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. UPD: We can change queries to detect 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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