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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-82124] Investigate safety of multiple acquisitions of CollectionRoutingInfo in nested aggregates</title>
                <link>https://jira.mongodb.org/browse/SERVER-82124</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;For nested aggregates in a sharded cluster which feature stages like $lookup, we often wind up acquiring multiple CollectionRoutingInfo objects (&lt;a href=&quot;https://github.com/mongodb/mongo/blob/e7dc7c9e239c1890caa679a7f4fd8af79270155c/src/mongo/s/query/cluster_aggregate.cpp#L403-L404&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;once at the top level&lt;/a&gt; and again when checking the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/4cffcc49e02348e40ce0652eb9abc60eeefa2c35/src/mongo/db/pipeline/process_interface/mongos_process_interface.cpp#L364-L368&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;shardedness of the inner collections&lt;/a&gt;. On its own, this isn&apos;t a problem because usually these involve different collections (so, conceptually, separate CollectionRoutingInfo objects) and ultimately the checks are used to inform routing decisions (that is, choosing the &apos;wrong&apos; host should mean that we get a suboptimal, but not incorrect, plan). However, there are a few cases that could be pose a problem&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;Cases where the target collection is the same as the inner collection&lt;/li&gt;
	&lt;li&gt;Cases where we have different collections, but which have the same database (i.e. all $lookup queries). This a problem potentially because the DBversion can change, between checks, indicating either a new owning shard for an unsplittable collection, or that the db was dropped and recreated.&#160;&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;This ticket tracks the work to investigate whether the cases described above can hit crashes or incorrect query results.&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="2472776">SERVER-82124</key>
            <summary>Investigate safety of multiple acquisitions of CollectionRoutingInfo in nested aggregates</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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-execution">Backlog - Query Execution</assignee>
                                    <reporter username="mihai.andrei@mongodb.com">Mihai Andrei</reporter>
                        <labels>
                    </labels>
                <created>Thu, 12 Oct 2023 15:37:32 +0000</created>
                <updated>Mon, 16 Oct 2023 11:05:54 +0000</updated>
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