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https://issues.apache.org/jira/browse/HIVE-22850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17033311#comment-17033311
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Rajesh Balamohan commented on HIVE-22850:
-----------------------------------------

Yes [~pvary] . Need to fix in separate ticket. Patch is for listing databases, 
which is not modifying the behavior "IN" clauses in TxnHandler.

> Optimise lock acquisition in TxnHandler
> ---------------------------------------
>
>                 Key: HIVE-22850
>                 URL: https://issues.apache.org/jira/browse/HIVE-22850
>             Project: Hive
>          Issue Type: Improvement
>          Components: Hive
>            Reporter: Rajesh Balamohan
>            Priority: Major
>         Attachments: HIVE-22850.1.patch, HIVE-22850.2.patch, Screenshot 
> 2020-02-07 at 4.14.51 AM.jpg
>
>
> With concurrent queries, time taken for lock acquisition increases 
> substantially. As part of lock acquisition in the query, 
> {{TxnHandler::checkLock}} gets invoked. This involves getting a mutex and 
> compare the locks being requested for, with that of existing locks in 
> {{HIVE_LOCKS}} table.
> With concurrent queries, time taken to do this check increase and this 
> significantly increases the time taken for getting mutex for other threads 
> (due to select for update). In a synthetic workload, it was in the order of 
> 10+ seconds. This codepath can be optimized when all lock requests are 
> SHARED_READ.
>  
>  
> !Screenshot 2020-02-07 at 4.14.51 AM.jpg|width=743,height=348!



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