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https://issues.apache.org/jira/browse/HIVE-17645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16211914#comment-16211914
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Eugene Koifman commented on HIVE-17645:
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There is a single LM for the warehouse. Having multiple TMs is like having
multiple Sessions - they can lock the same resources as long as requested locks
are compatible.
The issue is that each TM has it's own transaction context, i.e. in a different
transaction. For Spark reads, each Query Fragment uses a separate TM (and
ValidTxnList) so from the overall query perspective this creates Read Committed
semantics.
(to be continued)
> MM tables patch conflicts with HIVE-17482 (Spark/Acid integration)
> ------------------------------------------------------------------
>
> Key: HIVE-17645
> URL: https://issues.apache.org/jira/browse/HIVE-17645
> Project: Hive
> Issue Type: Sub-task
> Components: Transactions
> Affects Versions: 3.0.0
> Reporter: Eugene Koifman
> Labels: mm-gap-2
>
> MM code introduces
> {noformat}
> HiveTxnManager txnManager = SessionState.get().getTxnMgr()
> {noformat}
> in a number of places (e.g _DDLTask.generateAddMmTasks(Table tbl)_).
> HIVE-17482 adds a mode where a TransactionManager not associated with the
> session should be used. This will need to be addressed.
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