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From "Matthew Jacobs (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IMPALA-5602) All predicates pushed to Kudu with limit runs incorrectly as 'small query'
Date Thu, 29 Jun 2017 23:05:00 GMT
Matthew Jacobs created IMPALA-5602:
--------------------------------------

             Summary: All predicates pushed to Kudu with limit runs incorrectly as 'small
query'
                 Key: IMPALA-5602
                 URL: https://issues.apache.org/jira/browse/IMPALA-5602
             Project: IMPALA
          Issue Type: Bug
          Components: Frontend
    Affects Versions: Impala 2.8.0
            Reporter: Matthew Jacobs


When Kudu scans have predicates pushed to Kudu, the base implementation of  {{ScanNode.getInputCardinality()}}
is wrong:

{code}
  @Override
  public long getInputCardinality() {
    if (getConjuncts().isEmpty() && hasLimit()) return getLimit();
    return inputCardinality_;
  }
{code}

getConjuncts() won't contain the predicates pushed to Kudu. If such a query has a limit and
there aren't any conjuncts applied at the scan node, then this function will return the limit
as the input cardinality mistakenly.

This can result in a query running with the "small query" optimization when it should not
be, i.e. it runs on a single node with a single scanner thread.



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