docs/topics/impala_broadcast_bytes_limit.xml

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

    <title>BROADCAST_BYTES_LIMIT Query Option</title>

    <titlealts audience="PDF">

        <navtitle>BROADCAST_BYTES_LIMIT</navtitle>

    </titlealts>

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

    <conbody>

        <p>
            <indexterm audience="hidden">BROADCAST_BYTES_LIMIT query option</indexterm> Sets the limit
            for the size of the broadcast input based on estimated size.
        </p>
        <p>
            The Impala planner may in rare cases make a bad choice to broadcast a large table or intermediate
            result and encounter performance problems due to high memory pressure. Setting this limit will
            make the planner pick a partition based hash join instead of broadcast and avoid such performance problems.
        </p>
        <p conref="../shared/impala_common.xml#common/type_integer"/>

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

        <p>
            The default value is 34359738368 (32 GB). A value of 0 causes the option to be ignored.
        </p>
        <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock><![CDATA[
-- Change the limit to 16GB.
set broadcast_bytes_limit=17179869184;

-- Disable the BROADCAST_BYTES_LIMIT.
set broadcast_bytes_limit=0;
]]>
</codeblock>
    </conbody>
</concept>