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        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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            <title>[SERVER-68483] Use multikey metadata for more precise array estimation</title>
                <link>https://jira.mongodb.org/browse/SERVER-68483</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The optimizer collects metadata about path multikeyness (whether a path contains arrays).&lt;/p&gt;

&lt;p&gt;This metadata is available via the method ScanDefinition::getNonMultiKeyPathSet() that returns all paths that do NOT contain arrays.&lt;/p&gt;

&lt;p&gt;This task should use this metadata to improve cardinality estimation in the cases when such metadata is available. This metadata has priority over statistics - that is, if statistics says there are arrays, but the metadata says there aren&apos;t, we trust the metadata. Normally this shouldn&apos;t happen.&lt;/p&gt;

&lt;p&gt;We can also use this information for heuristic estimation, for instance a query that uses an array comparison value will return 0 matches if there are no arrays.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2104318">SERVER-68483</key>
            <summary>Use multikey metadata for more precise array estimation</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>
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                                    <resolution id="3">Duplicate</resolution>
                                        <assignee username="backlog-query-optimization">Backlog - Query Optimization</assignee>
                                    <reporter username="timour.katchaounov@mongodb.com">Timour Katchaounov</reporter>
                        <labels>
                            <label>M4</label>
                    </labels>
                <created>Tue, 2 Aug 2022 08:53:02 +0000</created>
                <updated>Mon, 5 Dec 2022 23:52:48 +0000</updated>
                            <resolved>Thu, 15 Sep 2022 07:46:17 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="4829413" author="JIRAUSER1258247" created="Thu, 15 Sep 2022 07:46:17 +0000"  >&lt;p&gt;This task won&apos;t be needed since &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-69591&quot; title=&quot;[CQF] Simplify non-sargable paths &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-69591&quot;&gt;&lt;del&gt;SERVER-69591&lt;/del&gt;&lt;/a&gt; will remove traverses over non-multikey paths.&lt;/p&gt;</comment>
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