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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-23808] Implement Index Choice based on Partial Filter Expression</title>
                <link>https://jira.mongodb.org/browse/SERVER-23808</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Request for index selection based solely on the partialFilterExpression.&lt;/p&gt;

&lt;p&gt;Currently, the query optimizer decides on an index based on the match and sort arguments of a query. With partial indexes, it will also consider the partialFilterExpression, but as implemented, it can still miss an index that would be performant on the query. &lt;/p&gt;

&lt;p&gt;Here&apos;s an example where the current implementation is sub-optimal:&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;   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.foo.dropIndex();&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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.foo.createIndex( { a : 1 }, { partialFilterExpression : { b : { $gte : 5 } } } );&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;for (i=1; i&amp;lt;=10; i++) { db.foo.insertOne( { a : i, b : i } ) };&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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-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.foo.find( { b : { $gte : 5 } }, { _id : 0, a : 1 } ).explain()&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;Desired result: The query uses the index, and it is a covered query&lt;br/&gt;
Current result: the query performs a collection scan&lt;br/&gt;
&lt;del&gt;Variation: db.foo.find( { a : { $exists: true }, b : { $gte : 5 } }, { _id : 0, a : 1 } ).explain() results in an index scan, but does not cover the query even though the index could cover this query.&lt;/del&gt;&lt;/p&gt;</description>
                <environment></environment>
        <key id="280875">SERVER-23808</key>
            <summary>Implement Index Choice based on Partial Filter Expression</summary>
                <type id="2" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14711&amp;avatarType=issuetype">New Feature</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="william.cross">William Cross</reporter>
                        <labels>
                    </labels>
                <created>Tue, 19 Apr 2016 19:13:31 +0000</created>
                <updated>Tue, 6 Dec 2022 04:27:36 +0000</updated>
                                            <version>3.2.5</version>
                                                    <component>Index Maintenance</component>
                                        <votes>0</votes>
                                    <watches>16</watches>
                                                                                                                <comments>
                            <comment id="1468407" author="william.cross" created="Tue, 3 Jan 2017 18:29:43 +0000"  >&lt;p&gt;I think this ticket is different in scope than &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-26896&quot; title=&quot;Use knowledge about partial index filter expression to determine whether $exists predicate can be covered&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-26896&quot;&gt;SERVER-26896&lt;/a&gt;. Per your reference to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-12869&quot; title=&quot;Index null values and missing values differently&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-12869&quot;&gt;SERVER-12869&lt;/a&gt; (Index null values and missing values differently), I&apos;m removing the mention of expecting a covered query for { a : &lt;/p&gt;
{ $exists : true }
&lt;p&gt; }.&lt;/p&gt;</comment>
                            <comment id="1465322" author="asya" created="Tue, 27 Dec 2016 15:30:09 +0000"  >&lt;p&gt;same as &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-26896&quot; title=&quot;Use knowledge about partial index filter expression to determine whether $exists predicate can be covered&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-26896&quot;&gt;SERVER-26896&lt;/a&gt;?&lt;/p&gt;</comment>
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                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="384363">SERVER-29247</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="322861">SERVER-26580</issuekey>
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