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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-15279] Disable hash-based index intersection (AND_HASH) by default</title>
                <link>https://jira.mongodb.org/browse/SERVER-15279</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Performance testing has suggested that hash-based index intersection, implemented by the AND_HASH query execution stage, does not offer a significant performance advantage for test workloads. This is due in part to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-12923&quot; title=&quot;Plan ranking is bad for plans with blocking stages&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-12923&quot;&gt;SERVER-12923&lt;/a&gt;, which describes how query optimization can suffer for plans that are not fully pipelined.&lt;/p&gt;

&lt;p&gt;Based on the results of this testing, we should disable hash-based intersection by default. It will be possible to re-enable AND_HASH at run time via:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;db.adminCommand({setParameter: 1, internalQueryPlannerEnableHashIntersection: 1});&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
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&lt;p/&gt;

&lt;p&gt;Sort-based intersection will be on by default and will not be affected by this change.&lt;/p&gt;</description>
                <environment></environment>
        <key id="158552">SERVER-15279</key>
            <summary>Disable hash-based index intersection (AND_HASH) by default</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="9">Done</resolution>
                                        <assignee username="david.storch@mongodb.com">David Storch</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                    </labels>
                <created>Tue, 16 Sep 2014 23:55:15 +0000</created>
                <updated>Thu, 28 Dec 2017 05:21:57 +0000</updated>
                            <resolved>Wed, 17 Sep 2014 13:54:37 +0000</resolved>
                                                    <fixVersion>2.6.5</fixVersion>
                    <fixVersion>2.7.7</fixVersion>
                                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="720753" author="xgen-internal-githook" created="Wed, 17 Sep 2014 13:56:55 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;dstorch&apos;, u&apos;name&apos;: u&apos;David Storch&apos;, u&apos;email&apos;: u&apos;david.storch@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-15279&quot; title=&quot;Disable hash-based index intersection (AND_HASH) by default&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-15279&quot;&gt;&lt;del&gt;SERVER-15279&lt;/del&gt;&lt;/a&gt; disable hash-based index intersection by default&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 5e2b3c29b438f936eeb0a675e70e0131ab4c145a)&lt;/p&gt;

&lt;p&gt;Conflicts:&lt;br/&gt;
	src/mongo/dbtests/plan_ranking.cpp&lt;br/&gt;
Branch: v2.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/775777b99c575edff05262140fbd529316aee939&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/775777b99c575edff05262140fbd529316aee939&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="720747" author="xgen-internal-githook" created="Wed, 17 Sep 2014 13:53:49 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;dstorch&apos;, u&apos;name&apos;: u&apos;David Storch&apos;, u&apos;email&apos;: u&apos;david.storch@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-15279&quot; title=&quot;Disable hash-based index intersection (AND_HASH) by default&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-15279&quot;&gt;&lt;del&gt;SERVER-15279&lt;/del&gt;&lt;/a&gt; disable hash-based index intersection by default&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/8baf068f5c7bcb52c7cc19bd6343fc2569cd92fc&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/8baf068f5c7bcb52c7cc19bd6343fc2569cd92fc&lt;/a&gt;&lt;/p&gt;</comment>
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            <issuekey id="153664">SERVER-14961</issuekey>
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            <issuekey id="167638">SERVER-15985</issuekey>
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