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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-10128) BytesBytesMultiHashMap does not allow concurrent read-only access
Date Wed, 01 Apr 2015 18:38:53 GMT

    [ https://issues.apache.org/jira/browse/HIVE-10128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14391176#comment-14391176
] 

Sergey Shelukhin commented on HIVE-10128:
-----------------------------------------

[~hagleitn] ping?

> BytesBytesMultiHashMap does not allow concurrent read-only access
> -----------------------------------------------------------------
>
>                 Key: HIVE-10128
>                 URL: https://issues.apache.org/jira/browse/HIVE-10128
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Gopal V
>            Assignee: Sergey Shelukhin
>             Fix For: llap
>
>         Attachments: HIVE-10128.01.patch, HIVE-10128.02.patch, HIVE-10128.03.patch, HIVE-10128.patch,
hashmap-after.png, hashmap-sync-source.png, hashmap-sync.png
>
>
> The multi-threaded performance takes a serious hit when LLAP shares hashtables between
the probe threads running in parallel. 
> !hashmap-sync.png!
> This is an explicit synchronized block inside ReusableRowContainer which triggers this
particular pattern.
> !hashmap-sync-source.png!
> Looking deeper into the code, the synchronization seems to be caused due to the fact
that WriteBuffers.setReadPoint modifies the otherwise read-only hashtable.
> To generate this sort of result, run LLAP at a WARN log-level, to avoid all the log synchronization
that otherwise affects the thread sync.



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