[jira] [Created] (HIVE-10128) LLAP: BytesBytesMultiHashMap does not allow concurrent read-only access

["Gopal V (JIRA)" <ji...@apache.org>]

Gopal V created HIVE-10128:
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             Summary: LLAP: BytesBytesMultiHashMap does not allow concurrent read-only access
                 Key: HIVE-10128
                 URL: https://issues.apache.org/jira/browse/HIVE-10128
             Project: Hive
          Issue Type: Sub-task
            Reporter: Gopal V
            Assignee: Sergey Shelukhin


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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