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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-48169] Optimize distinct count to avoid materializing any values outside the index</title>
                <link>https://jira.mongodb.org/browse/SERVER-48169</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Today we have two separate optimized index scans: COUNT_SCAN and DISTINCT_SCAN. COUNT_SCAN will return simple sentinel values as it scans the index, avoiding the cost of translating the index key format to the format the query plan needs/understands. DISTINCT_SCAN can seek over large sections of the index where the values are identical, but still materializes an object outside the index key for consumption by the query plan. These two optimizations could be combined in the case of a query like&lt;/p&gt;
&lt;p/&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;   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;{ $match: { &lt;/span&gt;&lt;/pre&gt;
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					&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;    value1: 1, &lt;/span&gt;&lt;/pre&gt;
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					&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;}},&lt;/span&gt;&lt;/pre&gt;
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						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
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&lt;p/&gt;

&lt;p&gt;This would lead to better performance, unclear how much.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1348999">SERVER-48169</key>
            <summary>Optimize distinct count to avoid materializing any values outside the index</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="charlie.swanson@mongodb.com">Charlie Swanson</reporter>
                        <labels>
                            <label>qopt-team</label>
                    </labels>
                <created>Tue, 12 May 2020 22:35:27 +0000</created>
                <updated>Tue, 6 Dec 2022 02:27:09 +0000</updated>
                                            <version>4.4.0</version>
                                                    <component>Aggregation Framework</component>
                    <component>Performance</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
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                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="103150">SERVER-12159</issuekey>
        </issuelink>
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