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Posted to dev@drill.apache.org by "Gautam Kumar Parai (JIRA)" <ji...@apache.org> on 2016/06/21 21:40:58 UTC

[jira] [Created] (DRILL-4743) HashJoin's not fully parallelized in query plan

Gautam Kumar Parai created DRILL-4743:
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             Summary: HashJoin's not fully parallelized in query plan
                 Key: DRILL-4743
                 URL: https://issues.apache.org/jira/browse/DRILL-4743
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.5.0
            Reporter: Gautam Kumar Parai
            Assignee: Gautam Kumar Parai


The underlying problem is filter selectivity under-estimate for a query with complicated predicates e.g. deeply nested and/or predicates. This leads to under parallelization of the major fragment doing the join. 

To really resolve this problem we need table/column statistics to correctly estimate the selectivity. However, in the absence of statistics OR even when existing statistics are insufficient to get a correct estimate of selectivity this will serve as a workaround.



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