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Change-Id: I07ec0a197de8a625788a3b0485d5ecf237e554ba Reviewed-on: http://gerrit.cloudera.org:8080/22576 Reviewed-by: Zoltan Borok-Nagy <boroknagyz@cloudera.com> Tested-by: Peter Rozsa <prozsa@cloudera.com>
95 lines
3.4 KiB
HTML
95 lines
3.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<meta name="copyright" content="(C) Copyright 2025" />
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<meta name="DC.rights.owner" content="(C) Copyright 2025" />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="THREAD_RESERVATION_LIMIT Query Option (Impala 3.1 or higher only)" />
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<meta name="DC.Relation" scheme="URI" content="../topics/impala_set.html" />
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<meta name="prodname" content="Impala" />
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<meta name="version" content="Impala 3.4.x" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="thread_reservation_limit" />
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<link rel="stylesheet" type="text/css" href="../commonltr.css" />
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<title>THREAD_RESERVATION_LIMIT Query Option (Impala 3.1 or higher only)</title>
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</head>
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<body id="thread_reservation_limit">
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<h1 class="title topictitle1" id="ariaid-title1">THREAD_RESERVATION_LIMIT Query Option (<span class="keyword">Impala 3.1</span> or higher only)</h1>
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<div class="body conbody">
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<p class="p">
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The <code class="ph codeph">THREAD_RESERVATION_LIMIT</code> 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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<a class="xref" href="impala_explain_plan.html#explain_plan">explain plan</a> in the
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“Per-Host Resource Reservation" line.
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</p>
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<p class="p">
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For example, an Impala administrator could set a default value of
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<code class="ph codeph">THREAD_RESERVATION_LIMIT=100</code> 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 class="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 <code class="ph codeph">THREAD_RESERVATION_LIMIT</code>
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value to apply to a specific query or session.
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</p>
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<div class="p">
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<div class="note note"><span class="notetitle">Note:</span>
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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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</div>
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</div>
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<p class="p">
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<strong class="ph b">Syntax:</strong> <code class="ph codeph">SET THREAD_RESERVATION_LIMIT=number;</code>
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</p>
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<p class="p">
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<strong class="ph b">Type:</strong> numeric
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</p>
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<p class="p">
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<strong class="ph b">Default:</strong> 3000
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</p>
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<p class="p">
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<strong class="ph b">Added in:</strong> <span class="keyword">Impala 3.1</span>
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</p>
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</div>
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<div class="related-links">
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_set.html">SET Statement</a></div>
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</div>
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</div></body>
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</html> |