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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
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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-82752] Writers can skip acquiring resource metadata lock for capped collection in 4.4 and older versions.</title>
                <link>https://jira.mongodb.org/browse/SERVER-82752</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Prior to 4.7.0 (&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-48312&quot; title=&quot;Remove support for supportsDocLocking = false&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-48312&quot;&gt;&lt;del&gt;SERVER-48312&lt;/del&gt;&lt;/a&gt;), the capped writers may skip acquiring the resource metadata lock, allowing concurrent writes to the capped collection.&#160; W&lt;b&gt;e require the resource metadata lock to serialize capped writes and maintain consistent natural ordering across the replica set.&#160; Disparity in natural ordering between the primary and secondaries can lead to &lt;a href=&quot;https://www.mongodb.com/docs/manual/core/capped-collections/#query-efficiency&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;tailable capped cursors&lt;/a&gt; skipping events upon resuming after a failover.&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;In 4.4, the resource metadata lock is acquired only when&#160;&lt;a href=&quot;https://github.com/10gen/mongo/blob/8c600e86ac6869aa618ba9f41a4fb471e3c01438/src/mongo/db/catalog/collection_impl.cpp#L255-L630%20is%20true&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;CollectionImpl::_needCappedLock is true&lt;/a&gt;. And, this flag is set to true only when the following&#160;&lt;a href=&quot;https://github.com/10gen/mongo/blob/8c600e86ac6869aa618ba9f41a4fb471e3c01438/src/mongo/db/catalog/collection_impl.cpp#L255&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;conditions&lt;/a&gt;&#160;are met:&lt;br/&gt;
1) supportsDocLocking() - returns global variable mongo::_supportsDocLocking&lt;br/&gt;
2) _recordStore-&amp;gt;isCapped()&lt;br/&gt;
3) _ns.db() != &quot;local&quot;&lt;/p&gt;

&lt;p&gt;After a node restart, supportsDocLocking() may erroneously return false, even if the storage engine is WiredTiger. That&apos;s because, as part of storage startup recovery procedure, &lt;tt&gt;initializeStorageEngine()&lt;/tt&gt;&#160;first&#160; loads the catalog and initialize the collection&#160;&lt;a href=&quot;https://github.com/10gen/mongo/blob/8c600e86ac6869aa618ba9f41a4fb471e3c01438/src/mongo/db/storage/storage_engine_init.cpp#L118&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;&#160;using the default value of mongo::_supportsDocLocking (&#160;&lt;a href=&quot;https://github.com/10gen/mongo/blob/8c600e86ac6869aa618ba9f41a4fb471e3c01438/src/mongo/db/service_context.cpp#L99&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;false&lt;/a&gt;&#160;), before&#160;&lt;a href=&quot;https://github.com/10gen/mongo/blob/8c600e86ac6869aa618ba9f41a4fb471e3c01438/src/mongo/db/storage/storage_engine_init.cpp#L177&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;initializing mongo::_supportsDocLocking with the correct true value&lt;/a&gt;&lt;/p&gt;</description>
                <environment></environment>
        <key id="2489949">SERVER-82752</key>
            <summary>Writers can skip acquiring resource metadata lock for capped collection in 4.4 and older versions.</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</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="2">Won&apos;t Fix</resolution>
                                        <assignee username="alan.zheng@mongodb.com">Alan Zheng</assignee>
                                    <reporter username="suganthi.mani@mongodb.com">Suganthi Mani</reporter>
                        <labels>
                    </labels>
                <created>Fri, 3 Nov 2023 06:20:40 +0000</created>
                <updated>Mon, 20 Nov 2023 22:02:53 +0000</updated>
                            <resolved>Tue, 14 Nov 2023 14:51:53 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>4</watches>
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                                                                <inwardlinks description="is related to">
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            <issuekey id="2474120">SERVER-82180</issuekey>
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                            <attachment id="487763" name="HELP-51123.repro" size="1001" author="suganthi.mani@mongodb.com" created="Mon, 6 Nov 2023 22:10:55 +0000"/>
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