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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-9199) Excessive exclusive lock used in some DDLs with DummyTxnManager
Date Wed, 24 Dec 2014 00:15:13 GMT

    [ https://issues.apache.org/jira/browse/HIVE-9199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14257712#comment-14257712
] 

Alan Gates commented on HIVE-9199:
----------------------------------

+1.  I didn't actually write this code, I just moved it to DummyTxnManager from Driver. But
looking over the patch, it makes sense.  Completeness doesn't have any meaning for DDL, only
for DML.

> Excessive exclusive lock used in some DDLs with DummyTxnManager
> ---------------------------------------------------------------
>
>                 Key: HIVE-9199
>                 URL: https://issues.apache.org/jira/browse/HIVE-9199
>             Project: Hive
>          Issue Type: Bug
>          Components: Locking
>            Reporter: Chaoyu Tang
>            Assignee: Chaoyu Tang
>         Attachments: HIVE-9199.patch
>
>
> In DummyTxnManager, the lockMode for a WriteEntity (e.g. database, table) is determined
by "complete" instead of its writeType. But since DDL output WriteEntity is usually complete,
some DDL operations might be given exclusive locks which are actually not needed, which causes
unnecessary locking contention. For example, in createTable, DummyTxnManager suggests an exclusive
lock to table database writeentity since it is complete.



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