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From "Gopal V (JIRA)" <>
Subject [jira] [Updated] (HIVE-10128) LLAP: BytesBytesMultiHashMap does not allow concurrent read-only access
Date Sat, 28 Mar 2015 03:59:52 GMT


Gopal V updated HIVE-10128:
    Attachment: hashmap-after.png

Fix looks good, the hashmap sync points have gone away from the inner loops.


The orange sections are the IO elevator lagging behind the map-join operator.

Found other init-time lock sections, will file more JIRAs.

> LLAP: BytesBytesMultiHashMap does not allow concurrent read-only access
> -----------------------------------------------------------------------
>                 Key: HIVE-10128
>                 URL:
>             Project: Hive
>          Issue Type: Sub-task
>            Reporter: Gopal V
>            Assignee: Sergey Shelukhin
>         Attachments: 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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