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From "Wei Zheng (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-12996) Temp tables shouldn't be locked
Date Tue, 03 May 2016 23:32:12 GMT

    [ https://issues.apache.org/jira/browse/HIVE-12996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15269840#comment-15269840
] 

Wei Zheng commented on HIVE-12996:
----------------------------------

The original symptom was that temp table records show up in metastore tables for ACID. But
the root cause is we locked temporary table the same way as we do for regular table.

Since temp tables are only visible to current session, there cannot be concurrent operations
on them, thus unnecessary to lock them.

> Temp tables shouldn't be locked
> -------------------------------
>
>                 Key: HIVE-12996
>                 URL: https://issues.apache.org/jira/browse/HIVE-12996
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>    Affects Versions: 2.0.0
>            Reporter: Wei Zheng
>            Assignee: Wei Zheng
>
> Internally, INSERT INTO ... VALUES statements use temp table to accomplish its functionality.
But temp tables shouldn't be stored in the metastore tables for ACID, because they are by
definition only visible inside the session that created them, and we don't allow multiple
threads inside a session. If a temp table is used in a query, it should be ignored by lock
manager.
> {code}
> mysql> select * from COMPLETED_TXN_COMPONENTS;
> +-----------+--------------+-----------------------+------------------+
> | CTC_TXNID | CTC_DATABASE | CTC_TABLE             | CTC_PARTITION    |
> +-----------+--------------+-----------------------+------------------+
> |         1 | acid         | t1                    | NULL             |
> |         1 | acid         | values__tmp__table__1 | NULL             |
> |         2 | acid         | t1                    | NULL             |
> |         2 | acid         | values__tmp__table__2 | NULL             |
> |         3 | acid         | values__tmp__table__3 | NULL             |
> |         3 | acid         | t1                    | NULL             |
> |         4 | acid         | values__tmp__table__1 | NULL             |
> |         4 | acid         | t2p                   | ds=today         |
> |         5 | acid         | values__tmp__table__1 | NULL             |
> |         5 | acid         | t3p                   | ds=today/hour=12 |
> +-----------+--------------+-----------------------+------------------+
> {code}



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