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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-19416) Create single version transactional table metastore statistics for aggregation queries
Date Wed, 13 Jun 2018 00:38:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-19416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16510455#comment-16510455
] 

Sergey Shelukhin commented on HIVE-19416:
-----------------------------------------

Wouldn't 1.1 case be also detected by 1.2, assuming these two checks/alterations of tables
are safe for races? I guess one case could be when table data is affected without creating
a txn, so txn state cannot be recorded... however, if such changes exist (I'm not sure they
do) how are they protected from races? is it by ACID locks? Just checking.
If my assumptions are correct (alter doesn't create txn/writeId but is safe due to locks),
it might be cleaner for txn tables to not have the parameter stored, but instead just unset
the txnId/writeIds data. If it's unset it will never match any query, which is the intention.
The parameter can just be generated at read time, and not exist in DB.
3.1-2 I don't think anybody's working on that. If stats optimizer gets write IDs but then
some in-flight txn commits before Driver gets locks and writeIds, it could mean stats optimizer
picks different data than the actual query would pick. So that is a problem.

> Create single version transactional table metastore statistics for aggregation queries
> --------------------------------------------------------------------------------------
>
>                 Key: HIVE-19416
>                 URL: https://issues.apache.org/jira/browse/HIVE-19416
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>            Reporter: Steve Yeom
>            Assignee: Steve Yeom
>            Priority: Major
>
> The system should use only statistics for aggregation queries like count on transactional
tables.



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