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Change-Id: I86116cb9163b91133d17b1bb3f40af9e636f02cf Reviewed-on: http://gerrit.cloudera.org:8080/11309 Reviewed-by: Alex Rodoni <arodoni@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
87 lines
2.4 KiB
XML
87 lines
2.4 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="enable_expr_rewrites">
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<title>ENABLE_EXPR_REWRITES Query Option</title>
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<titlealts audience="PDF">
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<navtitle>ENABLE_EXPR_REWRITES</navtitle>
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</titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Impala Query Options"/>
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<data name="Category" value="Troubleshooting"/>
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<data name="Category" value="Performance"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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The <codeph>ENABLE_EXPR_REWRITES</codeph> query option controls whether to enable or
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disable the query compile time optimizations. These optimizations rewrite the expression
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trees to a more compact and optimized form that helps avoid redundant expression
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evaluation at run time. Performance optimizations controlled by this query option include:
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</p>
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<ul>
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<li>
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Constant folding (added in <keyword keyref="impala28">)</keyword>
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</li>
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<li>
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Extracting common conjuncts from disjunctions (added in
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<keyword
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keyref="impala28">)</keyword>
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</li>
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<li>
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Simplify conditionals with constant conditions (added in
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<keyword
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keyref="impala29">)</keyword>
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</li>
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</ul>
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<p>
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Set the option to <codeph>false</codeph> or <codeph>0</codeph> to disable the performance
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optimizations.
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</p>
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<p>
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<b>Type: </b><codeph>boolean</codeph>
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</p>
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<p>
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<b>Default:</b> <codeph>true</codeph> (<codeph>1</codeph>)
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</p>
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<p>
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<b>Added in:</b> <keyword keyref="impala28"/>
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</p>
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</conbody>
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</concept>
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