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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-23732] Aggregation should optimize an irrelevant $sort preceding a $group</title>
                <link>https://jira.mongodb.org/browse/SERVER-23732</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;At the moment, we execute the following pipeline:&lt;br/&gt;
{$sort: {a: 1}} {$group: {_id: &quot;$b&quot;}}&lt;br/&gt;
Despite the fact that the $sort has no effect upon the $group.&lt;/p&gt;

&lt;p&gt;We should change DocumentSourceSort::optimizeAt() to remove itself if the following stage is a $group that doesn&apos;t use any of the sort&apos;s keys.&lt;/p&gt;</description>
                <environment></environment>
        <key id="279826">SERVER-23732</key>
            <summary>Aggregation should optimize an irrelevant $sort preceding a $group</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="benjamin.murphy">Benjamin Murphy</reporter>
                        <labels>
                            <label>performance</label>
                    </labels>
                <created>Thu, 14 Apr 2016 19:58:43 +0000</created>
                <updated>Tue, 6 Dec 2022 04:27:59 +0000</updated>
                                                                            <component>Aggregation Framework</component>
                                        <votes>0</votes>
                                    <watches>6</watches>
                                                                                                                <comments>
                            <comment id="1708418" author="asya" created="Wed, 25 Oct 2017 13:51:54 +0000"  >&lt;p&gt;This optimization must not happen if $sort is able to use an index via pushdown into query subsystem.&lt;/p&gt;

&lt;p&gt;Also if following $group does anything with full document (i.e. $push &quot;$$ROOT&quot; into an array) then that should be considered as &quot;using&quot; sort keys as the sort will determine the order of the documents in that array.&lt;/p&gt;</comment>
                            <comment id="1237293" author="rassi@10gen.com" created="Fri, 15 Apr 2016 16:25:07 +0000"  >&lt;p&gt;FWIW, I&apos;m somewhat skeptical about making the server responsible for removing predicates or pipeline stages that have no effect on the result set.  These kinds of optimizations are trivial for users to apply themselves; doing it on the server side encourages poor application design patterns, requires server code that has to be maintained, and slows down well-written application code by adding additional run-time analysis.&lt;/p&gt;</comment>
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                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="201429">SERVER-18287</issuekey>
        </issuelink>
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                                        <issuelink>
            <issuekey id="377780">SERVER-28980</issuekey>
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            <issuelink>
            <issuekey id="73561">SERVER-9507</issuekey>
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