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eadd35f6d5
The recent documentation formatting changes introduced the navigation panel on the left. However, due to the length of the query options navigation title these could overlap with the documentation paragraphs. This commit removes the underscores from the navigation titles of the query options, so browsers can break them into multiple lines. Additionally, the "SET" and "Query Options for the SET Statement" pages are merged to save some more space for the query option navigation titles. Testing: - Built the documentation and tested manually Change-Id: Icec787d7a2af848aaaff65be2ecf311a5ce8fe7f Reviewed-on: http://gerrit.cloudera.org:8080/20556 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Jason Fehr <jfehr@cloudera.com> Reviewed-by: Peter Rozsa <prozsa@cloudera.com> Reviewed-by: Tamas Mate <tmater@apache.org>
96 lines
3.2 KiB
XML
96 lines
3.2 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_limit">
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<title>THREAD_RESERVATION_LIMIT Query Option (<keyword keyref="impala31"/> or higher only)</title>
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<titlealts audience="PDF">
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<navtitle>THREAD RESERVATION 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_LIMIT</codeph> query option limits the number of reserved
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threads for a query on each node. The option is intended to prevent execution of complex
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queries that can consume excessive CPU or operating system resources on a single node.
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Queries that have more threads per node than this threshold are rejected by Impala’s
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admission controller before they start executing. You can see the number of reserved
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threads for a query in its
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<xref
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href="impala_explain_plan.xml#explain_plan">explain plan</xref> in the
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“Per-Host Resource Reservation" line.
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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_LIMIT=100</codeph> for a resource pool where they expect only
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relatively simple queries to run. This will reject queries that require more than 100
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reserved threads on a node, for example, queries with more than 100 fragments.
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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 <codeph>THREAD_RESERVATION_LIMIT</codeph>
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value to apply to a specific query or session.
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</p>
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<p>
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<note>
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The number of reserved threads on a node may be lower than the maximum value in the
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explain plan if not all fragments of that query are scheduled on every node.
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</note>
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</p>
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<p>
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<b>Syntax:</b> <codeph>SET THREAD_RESERVATION_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 rev="">
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<b>Default:</b> 3000
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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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