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https://issues.apache.org/jira/browse/HIVE-12636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15991064#comment-15991064
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Eugene Koifman commented on HIVE-12636:
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committed to master (3.0)
https://github.com/apache/hive/commit/21909601f8f5f9d8325774178aaaa8fb3c26a764
thanks Wei for the review
> Ensure that all queries (with DbTxnManager) run in a transaction
> ----------------------------------------------------------------
>
> Key: HIVE-12636
> URL: https://issues.apache.org/jira/browse/HIVE-12636
> Project: Hive
> Issue Type: Improvement
> Components: Transactions
> Affects Versions: 1.0.0
> Reporter: Eugene Koifman
> Assignee: Eugene Koifman
> Priority: Critical
> Fix For: 3.0.0
>
> Attachments: HIVE-12636.01.patch, HIVE-12636.02.patch,
> HIVE-12636.03.patch, HIVE-12636.04.patch, HIVE-12636.05.patch,
> HIVE-12636.06.patch, HIVE-12636.07.patch, HIVE-12636.09.patch,
> HIVE-12636.10.patch, HIVE-12636.12.patch, HIVE-12636.13.patch,
> HIVE-12636.17.patch
>
>
> Assuming Hive is using DbTxnManager
> Currently (as of this writing only auto commit mode is supported), only
> queries that write to an Acid table start a transaction.
> Read-only queries don't open a txn but still acquire locks.
> This makes internal structures confusing/odd.
> The are constantly 2 code paths to deal with which is inconvenient and error
> prone.
> Also, a txn id is convenient "handle" for all locks/resources within a txn.
> Doing thing would mean the client no longer needs to track locks that it
> acquired. This enables further improvements to metastore side of Acid.
> # add metastore call to openTxn() and acquireLocks() in a single call. this
> it to make sure perf doesn't degrade for read-only query. (Would also be
> useful for auto commit write queries)
> # Should RO queries generate txn ids from the same sequence? (they could for
> example use negative values of a different sequence). Txnid is part of the
> delta/base file name. Currently it's 7 digits. If we use the same sequence,
> we'll exceed 7 digits faster. (possible upgrade issue). On the other hand
> there is value in being able to pick txn id and commit timestamp out of the
> same logical sequence.
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