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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-52911] A lock-free read must not be able to acquire old in-memory Collection state and new on-disk collection state between a MODE_X operation storage write and onCommit handler CollectionCatalog updates</title>
                <link>https://jira.mongodb.org/browse/SERVER-52911</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;&lt;b&gt;This will only be a problem for lock-free reads, that bypass the atomicity of a collection MODE_X locked catalog operation&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;A lock free read can momentarily see an old version of the in-memory Collection state and a newer version of the on-disk collection state&lt;/p&gt;</description>
                <environment></environment>
        <key id="1544101">SERVER-52911</key>
            <summary>A lock-free read must not be able to acquire old in-memory Collection state and new on-disk collection state between a MODE_X operation storage write and onCommit handler CollectionCatalog updates</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="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="13202">Works as Designed</resolution>
                                        <assignee username="henrik.edin@mongodb.com">Henrik Edin</assignee>
                                    <reporter username="dianna.hohensee@mongodb.com">Dianna Hohensee</reporter>
                        <labels>
                    </labels>
                <created>Tue, 17 Nov 2020 15:19:06 +0000</created>
                <updated>Fri, 27 Oct 2023 13:52:35 +0000</updated>
                            <resolved>Fri, 4 Dec 2020 17:39:09 +0000</resolved>
                                                                    <component>Storage</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="3516661" author="henrik.edin" created="Fri, 4 Dec 2020 17:39:09 +0000"  >&lt;p&gt;Closing this as WAD. Has brainstormed with Dianna and Benety and don&apos;t believe this is causing any issue with lock free reads.&lt;/p&gt;

&lt;p&gt;createIndex: the index would be avaliable in the storage snapshot but not in the in-memory collection/index catalog. A query would simply not use the index which is fine.&lt;/p&gt;

&lt;p&gt;createCollection is protected by Collection::isCommitted and is not causing a problem.&lt;/p&gt;

&lt;p&gt;dropIndex/dropCollection is using the ident reaper and we&apos;re still holding a reference to the ident so it won&apos;t actually be removed from the storage engine&lt;/p&gt;

&lt;p&gt;collMod operations are affecting writes not reads, like the Validator. If this does not match it is not causing a problem.&lt;/p&gt;

&lt;p&gt;Last when we assert that durable state is matching the in-memory catalog we are holding locks so this is not affecting lock free reads. Example: &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46befe17d5d41b52808af01ef680a3405e113792/src/mongo/db/catalog/database_impl.cpp#L498-L499&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/46befe17d5d41b52808af01ef680a3405e113792/src/mongo/db/catalog/database_impl.cpp#L498-L499&lt;/a&gt;&lt;/p&gt;</comment>
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