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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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<item>
            <title>[SERVER-43893] $sample should desugar to $meta:&quot;randVal&quot; sort followed by $limit</title>
                <link>https://jira.mongodb.org/browse/SERVER-43893</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;When &lt;tt&gt;$sample&lt;/tt&gt; cannot execute using the storage-engine optimized path, it executes in terms of a &lt;a href=&quot;https://github.com/mongodb/mongo/blob/150406020cc1b77e4b8ce411e4d5723d03e323ca/src/mongo/db/pipeline/document_source_sample.h&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;&lt;tt&gt;DocumentSourceSample&lt;/tt&gt;&lt;/a&gt;. The implementation of &lt;tt&gt;DocumentSourceSample&lt;/tt&gt; delegates to a &lt;tt&gt;DocumentSourceSort&lt;/tt&gt; stage, which is &lt;a href=&quot;https://github.com/mongodb/mongo/blob/150406020cc1b77e4b8ce411e4d5723d03e323ca/src/mongo/db/pipeline/document_source_sample.h#L77&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;held as a data member&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;The design of the query execution tree should typically compose operators by connecting them into a tree, rather than composing them by making one a data member of another. Therefore, we should improve the code by making &lt;tt&gt;$sample&lt;/tt&gt; execute as a $meta:&quot;randVal&quot; sort operator with a coalesced limit value. The value of the limit is determined by the user query&apos;s sample size. This alternative implementation could be achieved by desugaring the user&apos;s &lt;tt&gt;$sample&lt;/tt&gt; stage into a &lt;tt&gt;$sort&lt;/tt&gt; followed by a &lt;tt&gt;$limit&lt;/tt&gt;. This would rely on the planner to construct an execution tree which generates the &quot;randVal&quot; metadata then subsequently performs the &lt;tt&gt;$sort&lt;/tt&gt;-&lt;tt&gt;$limit&lt;/tt&gt; as a top-k sort.&lt;/p&gt;</description>
                <environment></environment>
        <key id="964801">SERVER-43893</key>
            <summary>$sample should desugar to $meta:&quot;randVal&quot; sort followed by $limit</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>
                    </labels>
                <created>Tue, 8 Oct 2019 18:27:10 +0000</created>
                <updated>Tue, 6 Dec 2022 02:45:21 +0000</updated>
                                                                            <component>Aggregation Framework</component>
                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="3084333" author="david.storch" created="Wed, 13 May 2020 18:35:04 +0000"  >&lt;p&gt;I&apos;m removing this ticket from the &quot;Unify PlanStage and DocumentSource&quot; project but keeping it on the backlog. I don&apos;t think there is a strong motivation for scheduling it right now.&lt;/p&gt;</comment>
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