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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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            <title>[SERVER-42008] Simultaneous sharded collection drops do not have a total ordering in change streams</title>
                <link>https://jira.mongodb.org/browse/SERVER-42008</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;At present, when dropping a sharded collection, the &lt;tt&gt;drop&lt;/tt&gt; command is &lt;a href=&quot;https://github.com/mongodb/mongo/blob/491d4e528a91b04e8b20f2ddf0d1d88758599d6a/src/mongo/db/s/config/sharding_catalog_manager_collection_operations.cpp#L215-L228&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;dispatched sequentially to each shard&lt;/a&gt;. This means that each successive &lt;tt&gt;drop&lt;/tt&gt; always has a higher &lt;tt&gt;clusterTime&lt;/tt&gt; than its predecessor, such that the drop events appear in a change stream with a specific ordering.&lt;/p&gt;

&lt;p&gt;However, this ordering is due purely to current sharding mechanics and is not reflected in the resume token format. If a sharded collection were to be dropped on two or more shards at the same &lt;tt&gt;clusterTime&lt;/tt&gt; - as might happen if the sharding team decides to parallelize the collection drop operation - then the events on each shard would produce identical resume tokens, since they all have the same UUID and no &lt;tt&gt;documentKey&lt;/tt&gt;. This would lead to exactly the same ordering fiasco as described in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-34554&quot; title=&quot;Database drops do not have a total ordering in a change stream&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-34554&quot;&gt;SERVER-34554&lt;/a&gt;, and for the same reasons.&lt;/p&gt;

&lt;p&gt;If and when we decide to update the resume token format to address &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-34554&quot; title=&quot;Database drops do not have a total ordering in a change stream&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-34554&quot;&gt;SERVER-34554&lt;/a&gt;, we should make sure to address this potential future problem as well.&lt;/p&gt;</description>
                <environment></environment>
        <key id="828096">SERVER-42008</key>
            <summary>Simultaneous sharded collection drops do not have a total ordering in change streams</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="bernard.gorman@mongodb.com">Bernard Gorman</reporter>
                        <labels>
                            <label>change-streams-improvements</label>
                    </labels>
                <created>Fri, 28 Jun 2019 17:00:16 +0000</created>
                <updated>Tue, 6 Dec 2022 02:55:31 +0000</updated>
                                                                            <component>Aggregation Framework</component>
                                        <votes>0</votes>
                                    <watches>4</watches>
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