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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-38585] Add no-op delimiter stage to aggregation to prevent pipeline optimizations</title>
                <link>https://jira.mongodb.org/browse/SERVER-38585</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;MongoDB will perform a variety of &lt;a href=&quot;https://docs.mongodb.com/manual/core/aggregation-pipeline-optimization/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;sequencing and coalescing optimizations to an aggregation pipeline&lt;/a&gt;.&#160; These are very helpful and the list of available modifications continues to grow over time.&lt;/p&gt;

&lt;p&gt;However in some situations these modifications have a negative impact on performance.&#160; In such cases, it would be beneficial to have additional control over how the pipeline is split.&lt;/p&gt;

&lt;p&gt;As an arbitrary example, consider that there is a workaround in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-7568&quot; title=&quot;Aggregation framework favors non-blocking sorts&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-7568&quot;&gt;&lt;del&gt;SERVER-7568&lt;/del&gt;&lt;/a&gt; that involves injecting a &lt;tt&gt;$project&lt;/tt&gt; between a &lt;tt&gt;$match&lt;/tt&gt; and &lt;tt&gt;$sort&lt;/tt&gt;&#160;to modify the indices eligible for use by the operation.&#160; Notably&#160;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-26442&quot; title=&quot;Push $sort before $project and $addFields&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-26442&quot;&gt;SERVER-26442&lt;/a&gt; is a request to introduce an additional optimization that would &quot;break&quot; this workaround.&#160; For that reason, workaround such as that are not something that we would guarantee to behave the same across versions.&#160;&#160;&lt;/p&gt;

&lt;p&gt;Introducing a dedicated stage such as&#160; {&lt;tt&gt;$hint: {delimitPipeline: true&lt;/tt&gt;}} would provide additional control if needed in specific situations.&#160;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="652100">SERVER-38585</key>
            <summary>Add no-op delimiter stage to aggregation to prevent pipeline optimizations</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="christopher.harris@mongodb.com">Chris Harris</reporter>
                        <labels>
                    </labels>
                <created>Wed, 12 Dec 2018 22:08:42 +0000</created>
                <updated>Thu, 26 Jan 2023 16:15:09 +0000</updated>
                                                                            <component>Aggregation Framework</component>
                                        <votes>1</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="2093435" author="asya" created="Mon, 17 Dec 2018 20:41:24 +0000"  >&lt;p&gt;Interesting idea.&#160; If we had some sort of $tee it could serve a similar purpose (indicating that documents are needed to examine as they are at this point in the pipeline).&#160; Then the actual output of the documents could be optional.&#160; &lt;img class=&quot;emoticon&quot; src=&quot;https://jira.mongodb.org/images/icons/emoticons/smile.png&quot; height=&quot;16&quot; width=&quot;16&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</comment>
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