docs/topics/impala_shuffle_distinct_exprs.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="shuffle_distinct_exprs">

  <title>SHUFFLE_DISTINCT_EXPRS Query Option</title>

  <titlealts audience="PDF">

    <navtitle>SHUFFLE_DISTINCT_EXPRS</navtitle>

  </titlealts>

  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Query Options"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      The <codeph>SHUFFLE_DISTINCT_EXPRS</codeph> query option controls the
      shuffling behavior when a query has both grouping and distinct expressions.
      Impala can optionally include the distinct expressions in the hash exchange
      to spread the data among more nodes. However, this plan requires one more
      hash exchange phase.
    </p>

    <p>
      It is recommended that you turn off this option if the NDVs of the grouping
      expressions are high.
    </p>

    <p conref="../shared/impala_common.xml#common/type_boolean"/>

    <p conref="../shared/impala_common.xml#common/default_false"/>

  </conbody>

</concept>