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Change-Id: Iefcec53a6272a9221800678b9ed1ef52a898ed42 Reviewed-on: http://gerrit.cloudera.org:8080/11242 Reviewed-by: Alex Rodoni <arodoni@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
88 lines
3.0 KiB
XML
88 lines
3.0 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="thread_reservation_aggregate_limit">
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<title>THREAD_RESERVATION_AGGREGATE_LIMIT Query Option (<keyword
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keyref="impala31"/> or higher only)</title>
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<titlealts audience="PDF">
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<navtitle>THREAD_RESERVATION_AGGREGATE_LIMIT</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="Scalability"/>
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<data name="Category" value="Memory"/>
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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>
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The <codeph>THREAD_RESERVATION_AGGREGATE_LIMIT</codeph> query option limits the number of
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reserved threads for a query across all nodes on which it is executing. The option is
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intended to prevent execution of complex queries that can consume excessive CPU or
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operating system resources on a cluster. Queries that have more threads than this
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threshold are rejected by Impala’s admission controller before they start executing.
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</p>
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<p>
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For example, an Impala administrator could set a default value of
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<codeph>THREAD_RESERVATION_AGGREGATE_LIMIT=2000</codeph> for a resource pool on a 100 node
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where they expect only relatively simple queries with less than 20 threads per node to
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run. This will reject queries that require more than 2000 reserved threads across all
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nodes, for example a query with 21 fragments running on all 100 nodes of the cluster.
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</p>
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<p>
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You can override the default value per-query or per-session, in the same way as other
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query options, if you do not want the default
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<codeph>THREAD_RESERVATION_AGGREGATE_LIMIT</codeph> value to apply to a specific query or
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session.
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</p>
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<p>
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<b>Syntax:</b> <codeph>SET THREAD_RESERVATION_AGGREGATE_LIMIT=number;</codeph>
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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 (no limit)
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</p>
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<p>
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<b>Added in:</b> <keyword keyref="impala31"/>
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</p>
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</conbody>
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</concept>
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