[jira] [Created] (HIVE-5705) TopN might use better heuristic for disable

["Sergey Shelukhin (JIRA)" <ji...@apache.org>]

Sergey Shelukhin created HIVE-5705:
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             Summary: TopN might use better heuristic for disable
                 Key: HIVE-5705
                 URL: https://issues.apache.org/jira/browse/HIVE-5705
             Project: Hive
          Issue Type: Improvement
            Reporter: Sergey Shelukhin
            Priority: Minor


Right now, if TopN overruns memory threshold it disables itself if it couldn't directly exclude rows as they are sent; it doesn't count evictions that were initially put in the heap and then superceded for this purpose. 
It's reasonable in most cases, but if N is relatively small, and map output is large, the cost could still be worth it even if rows don't get excluded. So we'd pay some memory copies but emit much less rows.



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