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<?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>
<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"/>
<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.
<b>Type:</b> numeric (0, 1)
or corresponding mnemonic strings (<codeph>NONE</codeph>, <codeph>HT_BUCKET</codeph>).
<b>Default:</b> 1 (equivalent to <codeph>HT_BUCKET</codeph>)
<p conref="../shared/impala_common.xml#common/added_in_260"/>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
The default mode is 1, which means that hash table buckets are
prefetched during join query processing.
<p conref="../shared/impala_common.xml#common/related_info"/>
<xref href="impala_joins.xml#joins"/>,
<xref href="impala_perf_joins.xml#perf_joins"/>.