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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[DOCS-601] Clarify how $group and $sort operations utilize shards and mongos</title>
                <link>https://jira.mongodb.org/browse/DOCS-601</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;p&gt;The current documentation is not accurate with the aggregation framework&apos;s behavior.&lt;/p&gt;

&lt;blockquote&gt;
&lt;p&gt;When operating on a sharded collection, the aggregation pipeline is split into two parts. The aggregation framework pushes all of the operators up to and including the first $group or $sort to each shard. Then, a second pipeline on the mongos runs. This pipeline consists of the first $group or $sort and any remaining pipeline operators, and runs on the results received from the shards.&lt;/p&gt;

&lt;p&gt;The mongos pipeline merges $sort operations from the shards. The $group operator brings in any &#8220;sub-totals&#8221; from the shards and combines them: in some cases these may be structures. For example, the $avg expression maintains a total and count for each shard; mongos combines these values and then divides.&lt;/p&gt;&lt;/blockquote&gt;

&lt;p&gt;In reality (from &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=redbeard0531&quot; class=&quot;user-hover&quot; rel=&quot;redbeard0531&quot;&gt;redbeard0531&lt;/a&gt;):&lt;/p&gt;

&lt;blockquote&gt;&lt;p&gt;$sort only happens on the mongos, not on the shards. This will change in 2.4 for a $sort followed by a $limit.&lt;/p&gt;&lt;/blockquote&gt;</description>
                <environment></environment>
        <key id="53003">DOCS-601</key>
            <summary>Clarify how $group and $sort operations utilize shards and mongos</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="9">Done</resolution>
                                        <assignee username="sam.kleinman">Sam Kleinman</assignee>
                                    <reporter username="jmikola@mongodb.com">Jeremy Mikola</reporter>
                        <labels>
                    </labels>
                <created>Fri, 12 Oct 2012 14:41:57 +0000</created>
                <updated>Mon, 30 Oct 2023 22:34:35 +0000</updated>
                            <resolved>Thu, 8 Nov 2012 18:04:50 +0000</resolved>
                                    <version>v1.0</version>
                                    <fixVersion>Server_Docs_20231030</fixVersion>
                                    <component>manual</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="184158" author="auto" created="Thu, 8 Nov 2012 18:04:53 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;date&apos;: u&apos;2012-11-08T18:04:22Z&apos;, u&apos;email&apos;: u&apos;samk@10gen.com&apos;, u&apos;name&apos;: u&apos;Sam Kleinman&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-601&quot; title=&quot;Clarify how $group and $sort operations utilize shards and mongos&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-601&quot;&gt;&lt;del&gt;DOCS-601&lt;/del&gt;&lt;/a&gt;: correction about sorts and the aggregation framework.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/316b92cfc414939a5f5574e416aa039e231912d2&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/316b92cfc414939a5f5574e416aa039e231912d2&lt;/a&gt;&lt;/p&gt;</comment>
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