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    <title>MongoDB Jira</title>
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    <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>
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<item>
            <title>[SERVER-66283] Tailable cursors can miss writes on unreplicated capped collections</title>
                <link>https://jira.mongodb.org/browse/SERVER-66283</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Unreplicated capped collections do not serialize writes (see &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-21646&quot; title=&quot;Inserts and updates to replicated capped collections must be single threaded&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-21646&quot;&gt;&lt;del&gt;SERVER-21646&lt;/del&gt;&lt;/a&gt;), which means that tailable cursors can miss writes that commit in a different order than they were inserted.&lt;/p&gt;

&lt;p&gt;This problem has essentially existed since we implemented document-level locking in 3.0.&lt;/p&gt;

&lt;p&gt;Instead of also serializing writes to capped local collections, which would affect performance of inserts into the system.profile collection, I propose that we ban the usage of tailable cursors on unreplicated capped collections since they never worked correctly anyways.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2041348">SERVER-66283</key>
            <summary>Tailable cursors can miss writes on unreplicated capped collections</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="13201">Fixed</resolution>
                                        <assignee username="louis.williams@mongodb.com">Louis Williams</assignee>
                                    <reporter username="louis.williams@mongodb.com">Louis Williams</reporter>
                        <labels>
                    </labels>
                <created>Fri, 6 May 2022 16:04:01 +0000</created>
                <updated>Mon, 5 Feb 2024 21:45:00 +0000</updated>
                            <resolved>Thu, 29 Dec 2022 21:32:18 +0000</resolved>
                                                    <fixVersion>6.3.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="5082297" author="xgen-internal-githook" created="Thu, 29 Dec 2022 21:13:49 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Louis Williams&apos;, &apos;email&apos;: &apos;louis.williams@mongodb.com&apos;, &apos;username&apos;: &apos;louiswilliams&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66283&quot; title=&quot;Tailable cursors can miss writes on unreplicated capped collections&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66283&quot;&gt;&lt;del&gt;SERVER-66283&lt;/del&gt;&lt;/a&gt; Correct tailable cursor support on unreplicated capped collections&lt;/p&gt;

&lt;p&gt;This corrects previously incorrect behavior where tailable cursors on unreplicated capped&lt;br/&gt;
collections like the profile collection could miss writes&lt;/p&gt;

&lt;p&gt;This pushes non-oplog capped collection visibility logic outside of the storage engine layer&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/96573561ca19babfc0fa5f535c6cec095e703ebc&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/96573561ca19babfc0fa5f535c6cec095e703ebc&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5057557" author="gregory.noma" created="Thu, 15 Dec 2022 15:19:46 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=louis.williams%40mongodb.com&quot; class=&quot;user-hover&quot; rel=&quot;louis.williams@mongodb.com&quot;&gt;louis.williams@mongodb.com&lt;/a&gt; I see this is in Blocked but it&apos;s not linked as dependent as on anything, is there a ticket this can be linked to?&lt;/p&gt;</comment>
                            <comment id="4538634" author="louis.williams" created="Tue, 10 May 2022 15:54:10 +0000"  >&lt;p&gt;More context: we unintentionally broke tailable cursors on the system.profile collection in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61277&quot; title=&quot;Allow concurrent writes on capped clustered collections&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61277&quot;&gt;&lt;del&gt;SERVER-61277&lt;/del&gt;&lt;/a&gt; for 5.3.0 by no longer serializing writes, which was a request in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-55476&quot; title=&quot;Database profiling should not serialize writes on all collections&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-55476&quot;&gt;&lt;del&gt;SERVER-55476&lt;/del&gt;&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;We have three options:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Partially-revert the change in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61277&quot; title=&quot;Allow concurrent writes on capped clustered collections&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61277&quot;&gt;&lt;del&gt;SERVER-61277&lt;/del&gt;&lt;/a&gt; and serialize writes on system.profile again&lt;/li&gt;
	&lt;li&gt;Implement &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18934&quot; title=&quot;Don&amp;#39;t require storage engines to implement oplog visibility rules&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18934&quot;&gt;SERVER-18934&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;Ban tailable cursors on unreplicated capped collections. We don&apos;t think we should do this.&lt;/li&gt;
&lt;/ul&gt;
</comment>
                            <comment id="4531744" author="louis.williams" created="Fri, 6 May 2022 16:10:44 +0000"  >&lt;p&gt;This is essentially an alternative to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18934&quot; title=&quot;Don&amp;#39;t require storage engines to implement oplog visibility rules&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18934&quot;&gt;SERVER-18934&lt;/a&gt;, which is a decent amount of work.&lt;/p&gt;</comment>
                    </comments>
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            <issuekey id="2098545">SERVER-68271</issuekey>
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            <issuekey id="2567599">SERVER-86241</issuekey>
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