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From "Eugene Koifman (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-11833) TxnHandler heartbeat txn doesn't need serializable DB txn level
Date Fri, 25 Sep 2015 01:59:04 GMT

     [ https://issues.apache.org/jira/browse/HIVE-11833?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Eugene Koifman updated HIVE-11833:
----------------------------------
    Component/s: Transactions

> TxnHandler heartbeat txn doesn't need serializable DB txn level
> ---------------------------------------------------------------
>
>                 Key: HIVE-11833
>                 URL: https://issues.apache.org/jira/browse/HIVE-11833
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>            Reporter: Sergey Shelukhin
>            Assignee: Sergey Shelukhin
>             Fix For: 2.0.0
>
>         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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