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There are interactions between mt_dop and num_nodes and num_scanner_threads. Mention these in the docs. Change-Id: I3d9a6f56ffaf211d7d3ca1fad506ee83d516ccbd Reviewed-on: http://gerrit.cloudera.org:8080/17043 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
58 lines
2.0 KiB
XML
58 lines
2.0 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="num_scanner_threads">
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<title>NUM_SCANNER_THREADS Query Option</title>
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<titlealts audience="PDF"><navtitle>NUM_SCANNER_THREADS</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="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>
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<indexterm audience="hidden">NUM_SCANNER_THREADS query option</indexterm>
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Maximum number of scanner threads (on each node) used for each query. By default, Impala uses as many cores
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as are available (one thread per core). You might lower this value if queries are using excessive resources
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on a busy cluster. Impala imposes a maximum value automatically, so a high value has no practical effect.
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</p>
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<p>
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Has no effect if multi-threaded query execution is enabled, i.e.
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<codeph>MT_DOP</codeph> is greater than 0.
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</p>
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<p>
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<b>Type:</b> numeric
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</p>
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<p>
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<b>Default:</b> 0
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</p>
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</conbody>
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</concept>
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