docs/topics/impala_prefetch_mode.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="prefetch_mode" rev="2.6.0 IMPALA-3286">

  <title>PREFETCH_MODE Query Option (<keyword keyref="impala26"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>PREFETCH_MODE</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="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="2.6.0 IMPALA-3286">
      <indexterm audience="hidden">PREFETCH_MODE query option</indexterm>
      Determines whether the prefetching optimization is applied during
      join query processing.
    </p>

    <p>
      <b>Type:</b> numeric (0, 1)
      or corresponding mnemonic strings (<codeph>NONE</codeph>, <codeph>HT_BUCKET</codeph>).
    </p>

    <p>
      <b>Default:</b> 1 (equivalent to <codeph>HT_BUCKET</codeph>)
    </p>

    <p conref="../shared/impala_common.xml#common/added_in_260"/>

    <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
    <p>
      The default mode is 1, which means that hash table buckets are
      prefetched during join query processing.
    </p>

    <p conref="../shared/impala_common.xml#common/related_info"/>
    <p>
      <xref href="impala_joins.xml#joins"/>,
      <xref href="impala_perf_joins.xml#perf_joins"/>.
    </p>

  </conbody>
</concept>