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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
    </build-info>


<item>
            <title>[SERVER-56583] Push $setWindowFields to shards when shards contain whole partitions</title>
                <link>https://jira.mongodb.org/browse/SERVER-56583</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;It&apos;s safe to run the $setWindowFields stage on each shard independently as long as each partition lives on a single shard. That means the shard key must be at least as coarse as the partitionBy expression / the shard key must be constant within each partition.&lt;/p&gt;

&lt;p&gt;For example, given this query:&lt;/p&gt;
&lt;p/&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;  partitionBy: {state: &quot;$state&quot;, city: &quot;$city&quot;},&lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;
&lt;p&gt;This is safe to push down if the shard key is any of these:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;{state: 1, city: 1}&lt;/li&gt;
	&lt;li&gt;{city: 1, state: 1}&lt;/li&gt;
	&lt;li&gt;{state: 1}&lt;/li&gt;
	&lt;li&gt;{city: 1}
&lt;p&gt;In all these cases, the documents that the &apos;partitionBy&apos; groups together live on the same shard.&lt;/p&gt;&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;Some examples of shard keys that wouldn&apos;t allow this:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;{state: 1, city: 1, _id: 1}&lt;/li&gt;
	&lt;li&gt;{_id: 1}&lt;/li&gt;
	&lt;li&gt;{country: 1, state: 1, city: 1}&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;The analysis we&apos;d need seems similar to pushing down $match past $setWindowFields: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-56419&quot; title=&quot;Push down $match past $setWindowFields when it keeps/drops whole partitions&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-56419&quot;&gt;SERVER-56419&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;One problem is that we convert $setWindowFields with a partitionBy to a $sort + $_internalSetWindowFields before optimization. Pushing down the $sort wouldn&apos;t be valid.&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Maybe we should somehow delay introducing the $sort until after we&apos;ve done some optimization.&lt;/li&gt;
	&lt;li&gt;Maybe we can do something like &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-53638&quot; title=&quot;Enable pushdown of config.cache.chunks $lookup through $sort&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-53638&quot;&gt;&lt;del&gt;SERVER-53638&lt;/del&gt;&lt;/a&gt;, where we push a $lookup down through the mergesort part of a sharded sort.&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="1699775">SERVER-56583</key>
            <summary>Push $setWindowFields to shards when shards contain whole partitions</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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-execution">Backlog - Query Execution</assignee>
                                    <reporter username="david.percy@mongodb.com">David Percy</reporter>
                        <labels>
                    </labels>
                <created>Mon, 3 May 2021 20:21:20 +0000</created>
                <updated>Tue, 6 Dec 2022 01:21:23 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="4955939" author="JIRAUSER1264467" created="Fri, 4 Nov 2022 18:01:57 +0000"  >&lt;p&gt;Probably not high urgency, as 1% of customers use sharding and $setWindowFields is used by even fewer customers. Unless there&apos;s a specific customer who complains, I would say this is relatively low priority&lt;/p&gt;</comment>
                            <comment id="4387373" author="kyle.suarez" created="Wed, 2 Mar 2022 19:20:25 +0000"  >&lt;p&gt;This ticket got lost on the backlog; flagging for retriage.&lt;/p&gt;</comment>
                    </comments>
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                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="1583451">SERVER-53638</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="35285">SERVER-5477</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1693544">SERVER-56419</issuekey>
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