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https://issues.apache.org/jira/browse/HIVE-23725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17184162#comment-17184162
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Zoltan Haindrich commented on HIVE-23725:
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* I think using hooks is better - because it could give you more context about
the actual system's state...if some information is not yet accessible using the
hooks please try to extend the hooks with it...so that you can be notified/etc
* making the plugin optional could have been usefull in that case...when a
plugin doesn't work as expected; you could disable it - but in case it's burned
in..you can't disable it...
* I don't know why would you need to go over say
HIVE_QUERY_MAX_REEXECUTION_COUNT - I think if we try something for 3 times it
will likely not succeed after further attempts as well...
> ValidTxnManager snapshot outdating causing partial reads in merge insert
> ------------------------------------------------------------------------
>
> Key: HIVE-23725
> URL: https://issues.apache.org/jira/browse/HIVE-23725
> Project: Hive
> Issue Type: Bug
> Reporter: Peter Varga
> Assignee: Peter Varga
> Priority: Major
> Labels: pull-request-available
> Time Spent: 5h 40m
> Remaining Estimate: 0h
>
> When the ValidTxnManager invalidates the snapshot during merge insert and
> starts to read committed transactions that were not committed when the query
> compilation happened, it can cause partial read problems if the committed
> transaction created new partition in the source or target table.
> The solution should be not only fix the snapshot but also recompile the query
> and acquire the locks again.
> You could construct an example like this:
> 1. open and compile transaction 1 that merge inserts data from a partitioned
> source table that has a few partition.
> 2. Open, run and commit transaction 2 that inserts data to an old and a new
> partition to the source table.
> 3. Open, run and commit transaction 3 that inserts data to the target table
> of the merge statement, that will retrigger a snapshot generation in
> transaction 1.
> 4. Run transaction 1, the snapshot will be regenerated, and it will read
> partial data from transaction 2 breaking the ACID properties.
> Different setup.
> Switch the transaction order:
> 1. compile transaction 1 that inserts data to an old and a new partition of
> the source table.
> 2. compile transaction 2 that insert data to the target table
> 2. compile transaction 3 that merge inserts data from the source table to the
> target table
> 3. run and commit transaction 1
> 4. run and commit transaction 2
> 5. run transaction 3, since it cointains 1 and 2 in its snaphot the
> isValidTxnListState will be triggered and we do a partial read of the
> transaction 1 for the same reasons.
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