docs/topics/impala_disable_streaming_preaggregations.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="disable_streaming_preaggregations" rev="2.5.0 IMPALA-1305">

  <title>DISABLE_STREAMING_PREAGGREGATIONS Query Option (<keyword keyref="impala25"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>DISABLE_STREAMING_PREAGGREGATIONS</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Query Options"/>
      <data name="Category" value="Performance"/>
      <data name="Category" value="Aggregate Functions"/>
      <data name="Category" value="Troubleshooting"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="2.5.0 IMPALA-1305">
      <indexterm audience="hidden">DISABLE_STREAMING_PREAGGREGATIONS query option</indexterm>
      Turns off the <q>streaming preaggregation</q> optimization that is available in <keyword keyref="impala25_full"/>
      and higher. This optimization reduces unnecessary work performed by queries that perform aggregation
      operations on columns with few or no duplicate values, for example <codeph>DISTINCT <varname>id_column</varname></codeph>
      or <codeph>GROUP BY <varname>unique_column</varname></codeph>. If the optimization causes regressions in
      existing queries that use aggregation functions, you can turn it off as needed by setting this query option.
    </p>

    <p conref="../shared/impala_common.xml#common/type_boolean"/>
    <p conref="../shared/impala_common.xml#common/default_false_0"/>

    <note conref="../shared/impala_common.xml#common/one_but_not_true"/>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
    <p>
      Typically, queries that would require enabling this option involve very large numbers of
      aggregated values, such as a billion or more distinct keys being processed on each
      worker node.
    </p>

    <p conref="../shared/impala_common.xml#common/added_in_250"/>

  </conbody>
</concept>