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From "Gopal V (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-16329) TopN: TopNHash totalFreeMemory computation ignores free memory
Date Wed, 29 Mar 2017 22:44:41 GMT
Gopal V created HIVE-16329:
------------------------------

             Summary: TopN: TopNHash totalFreeMemory computation ignores free memory
                 Key: HIVE-16329
                 URL: https://issues.apache.org/jira/browse/HIVE-16329
             Project: Hive
          Issue Type: Bug
            Reporter: Gopal V


{code}
      // TODO: For LLAP, assumption is off-heap cache.
      final long memoryUsedPerExecutor = (memoryMXBean.getHeapMemoryUsage().getUsed() / numExecutors);
      // this is total free memory available per executor in case of LLAP
      totalFreeMemory = conf.getMaxMemoryAvailable() - memoryUsedPerExecutor;
{code}

{code}
exec.TopNHash: isTez parameters -615768144 = 5312782848 - 71142611912 / 12
{code}

This turns off the TopNHash entirely causing something trivial like 

{code}
select c_custkey, count(1) from customer group by c_custkey limit 10;
{code}

To shuffle 30M rows instead of 10.



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