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d484d2f684
This now gives a clean RAT check with bin/check-rat-report.py, which is one way for the Impala community to check compliance with ASF rules on intellectual property. Change-Id: I2ad06435f84a65ba126759e42a18fdaf52cd7036 Reviewed-on: http://gerrit.cloudera.org:8080/5232 Reviewed-by: Jim Apple <jbapple-impala@apache.org> Tested-by: Impala Public Jenkins Reviewed-by: John Russell <jrussell@cloudera.com>
64 lines
2.8 KiB
XML
64 lines
2.8 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="disable_streaming_preaggregations" rev="2.5.0 IMPALA-1305">
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<title>DISABLE_STREAMING_PREAGGREGATIONS Query Option (<keyword keyref="impala25"/> or higher only)</title>
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<titlealts audience="PDF"><navtitle>DISABLE_STREAMING_PREAGGREGATIONS</navtitle></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="Performance"/>
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<data name="Category" value="Aggregate Functions"/>
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<data name="Category" value="Troubleshooting"/>
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<data name="Category" value="Developers"/>
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<data name="Category" value="Data Analysts"/>
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</metadata>
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</prolog>
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<conbody>
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<p rev="2.5.0 IMPALA-1305">
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<indexterm audience="Cloudera">DISABLE_STREAMING_PREAGGREGATIONS query option</indexterm>
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Turns off the <q>streaming preaggregation</q> optimization that is available in <keyword keyref="impala25_full"/>
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and higher. This optimization reduces unnecessary work performed by queries that perform aggregation
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operations on columns with few or no duplicate values, for example <codeph>DISTINCT <varname>id_column</varname></codeph>
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or <codeph>GROUP BY <varname>unique_column</varname></codeph>. If the optimization causes regressions in
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existing queries that use aggregation functions, you can turn it off as needed by setting this query option.
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</p>
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<p conref="../shared/impala_common.xml#common/type_boolean"/>
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<p conref="../shared/impala_common.xml#common/default_false_0"/>
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<note conref="../shared/impala_common.xml#common/one_but_not_true"/>
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<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
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<p>
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Typically, queries that would require enabling this option involve very large numbers of
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aggregated values, such as a billion or more distinct keys being processed on each
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worker node.
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</p>
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<p conref="../shared/impala_common.xml#common/added_in_250"/>
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</conbody>
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</concept>
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