docs/topics/impala_enable_expr_rewrites.xml

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

  <title>ENABLE_EXPR_REWRITES Query Option</title>

  <titlealts audience="PDF">

    <navtitle>ENABLE_EXPR_REWRITES</navtitle>

  </titlealts>

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

  <conbody>

    <p>
      The <codeph>ENABLE_EXPR_REWRITES</codeph> query option controls whether to enable or
      disable the query compile time optimizations. These optimizations rewrite the expression
      trees to a more compact and optimized form that helps avoid redundant expression
      evaluation at run time. Performance optimizations controlled by this query option include:
    </p>

    <ul>
      <li>
        Constant folding (added in <keyword keyref="impala28">)</keyword>
      </li>

      <li>
        Extracting common conjuncts from disjunctions (added in
        <keyword
          keyref="impala28">)</keyword>
      </li>

      <li>
        Simplify conditionals with constant conditions (added in
        <keyword
          keyref="impala29">)</keyword>
      </li>
    </ul>

    <p>
      Set the option to <codeph>false</codeph> or <codeph>0</codeph> to disable the performance
      optimizations.
    </p>

    <p>
      <b>Type: </b><codeph>boolean</codeph>
    </p>

    <p>
      <b>Default:</b> <codeph>true</codeph> (<codeph>1</codeph>)
    </p>

    <p>
      <b>Added in:</b> <keyword keyref="impala28"/>
    </p>

  </conbody>

</concept>