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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
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    <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-12281] When choosing multikey index bounds, never choose a superset if a subset is available</title>
                <link>https://jira.mongodb.org/browse/SERVER-12281</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;For queries with multiple predicates over a multikey field, you can&apos;t intersect the index bounds. Suppose there is a multikey index on field &apos;a&apos;. The following query&lt;/p&gt;
&lt;p/&gt;
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&lt;p/&gt;
&lt;p&gt;would have empty index bounds if &apos;a&apos; were not a multikey field. Since it is multikey, however, we either use bounds&lt;/p&gt;
&lt;p/&gt;
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&lt;p/&gt;
&lt;p&gt;or&lt;/p&gt;
&lt;p/&gt;
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&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;
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						&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;[1, Infinity]&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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&lt;p/&gt;

&lt;p&gt;Which bounds to use is chosen arbitrarily. As an optimization, we could make sure that we always choose the &lt;em&gt;smallest&lt;/em&gt; interval over which to perform the index scan. For instance, for the query&lt;/p&gt;
&lt;p/&gt;
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					&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.t.find({a: {$gt: 4, $gte: 5}});&lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;
&lt;p&gt;we would choose&lt;/p&gt;
&lt;p/&gt;
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&lt;p/&gt;
&lt;p&gt;rather than&lt;/p&gt;
&lt;p/&gt;
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			&lt;/td&gt;
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&lt;p/&gt;
&lt;p&gt;because the former is a subset of the latter.&lt;/p&gt;</description>
                <environment></environment>
        <key id="105000">SERVER-12281</key>
            <summary>When choosing multikey index bounds, never choose a superset if a subset is available</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-query-optimization">Backlog - Query Optimization</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                            <label>asya</label>
                    </labels>
                <created>Tue, 7 Jan 2014 19:29:05 +0000</created>
                <updated>Tue, 6 Dec 2022 05:13:25 +0000</updated>
                                            <version>2.5.4</version>
                                                    <component>Querying</component>
                                        <votes>11</votes>
                                    <watches>23</watches>
                                                                                                                <comments>
                            <comment id="1071953" author="david.storch" created="Tue, 27 Oct 2015 18:32:16 +0000"  >&lt;p&gt;As of the fix for &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-16042&quot; title=&quot;Optimise $all/$and to select smallest subset as initial index bounds&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-16042&quot;&gt;&lt;del&gt;SERVER-16042&lt;/del&gt;&lt;/a&gt;, the server no longer chooses the multikey index bounds arbitrarily. Instead, the server will generate alternative plans using each possible set of bounds, and rank these candidates against one another. If a particular set of bounds is significantly more selective, this should be discovered during the plan ranking process.&lt;/p&gt;

&lt;p&gt;As an optimization, we could still consider suppressing generation of plans whose bounds are a superset of another plan&apos;s bounds. However, &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-16042&quot; title=&quot;Optimise $all/$and to select smallest subset as initial index bounds&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-16042&quot;&gt;&lt;del&gt;SERVER-16042&lt;/del&gt;&lt;/a&gt; solves the immediate problem and makes this work much less urgent.&lt;/p&gt;</comment>
                            <comment id="910081" author="david.storch" created="Mon, 11 May 2015 16:14:51 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=tredman%40fb.com&quot; class=&quot;user-hover&quot; rel=&quot;tredman@fb.com&quot;&gt;tredman@fb.com&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;An update on your question:&lt;/p&gt;

&lt;blockquote&gt;
&lt;p&gt;This bit us too. Query is in the form { foo: { $in: [ a ], $nin: [ b, c, ..., z ] } }. Basically results in a full index scan. Any chance of this getting back-ported to 2.6?&lt;/p&gt;&lt;/blockquote&gt;

&lt;p&gt;We have a fix for this query under related ticket &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18364&quot; title=&quot;Ensure non-negation predicates get chosen over negation predicates for multikey index bounds construction&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18364&quot;&gt;&lt;del&gt;SERVER-18364&lt;/del&gt;&lt;/a&gt;. The fix is currently in master, and will be available in 2.6.10 as well as 3.0.4. The RC process for 2.6.10 is set to begin within the next few weeks.&lt;/p&gt;

&lt;p&gt;Best,&lt;br/&gt;
Dave&lt;/p&gt;</comment>
                            <comment id="909325" author="asya" created="Sat, 9 May 2015 05:04:55 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=tredman%40fb.com&quot; class=&quot;user-hover&quot; rel=&quot;tredman@fb.com&quot;&gt;tredman@fb.com&lt;/a&gt; we can request a backport only once there is a fix committed to master.&lt;/p&gt;</comment>
                            <comment id="909259" author="tredman@fb.com" created="Fri, 8 May 2015 23:54:53 +0000"  >&lt;p&gt;This bit us too. Query is in the form { foo: &lt;/p&gt;
{ $in: [ a ], $nin: [ b, c, ..., z ] }
&lt;p&gt; }. Basically results in a full index scan. Any chance of this getting back-ported to 2.6?&lt;/p&gt;</comment>
                            <comment id="813217" author="sef@voxelbrain.com" created="Mon, 26 Jan 2015 17:29:04 +0000"  >&lt;p&gt;I was bitten by this as well, query went from 7ms to 71661ms after upgrade to MongoDB 2.6.7 (from 2.4.12). Query and details in case anyone is interested: &lt;a href=&quot;http://pastebin.com/Sca2c3qS&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://pastebin.com/Sca2c3qS&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="764389" author="boutell" created="Fri, 14 Nov 2014 15:23:40 +0000"  >&lt;p&gt;+1; I was surprised by the harsh slowdown imposed by the presence of $nin as well as $in.&lt;/p&gt;</comment>
                    </comments>
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            <issuekey id="157606">SERVER-15214</issuekey>
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            <issuekey id="163597">SERVER-15658</issuekey>
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