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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <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-41558] Make CollectionScan on oplog work without holding database/collection lock</title>
                <link>https://jira.mongodb.org/browse/SERVER-41558</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Currently, &lt;tt&gt;CollectionScan&lt;/tt&gt; eventually calls &lt;a href=&quot;https://github.com/mongodb/mongo/blob/661588a68066dcef3f7f3fea0af37ecebb23594a/src/mongo/db/exec/requires_collection_stage.h#L95-L101&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this&lt;/a&gt; which then calls &lt;tt&gt;databaseHolder-&amp;gt;getDb&lt;/tt&gt; where &lt;a href=&quot;https://github.com/mongodb/mongo/blob/661588a68066dcef3f7f3fea0af37ecebb23594a/src/mongo/db/catalog/database_holder_impl.cpp#L74&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;we invariant a database IS lock is held&lt;/a&gt;. &lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;mongod(void mongo::invariantWithLocation&amp;lt;bool&amp;gt;(bool const&amp;amp;, char const*, char const*, unsigned int) 0x3F) [0x5579e275041b]&lt;/span&gt;&lt;/pre&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;mongod(mongo::DatabaseHolderImpl::getDb(mongo::OperationContext*, mongo::StringData) const 0x91) [0x5579e314717f]&lt;/span&gt;&lt;/pre&gt;
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						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;mongod(mongo::RequiresCollectionStageBase&amp;lt;mongo::Collection const*&amp;gt;::getDatabaseEpoch(mongo::Collection const*) const 0x106) [0x5579e32ead18]&lt;/span&gt;&lt;/pre&gt;
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						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;mongod(mongo::RequiresCollectionStageBase&amp;lt;mongo::Collection const*&amp;gt;::RequiresCollectionStageBase(char const*, mongo::OperationContext*, mongo::Collection const*) 0xD6) [0x5579e32e9a4e]&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;mongod(mongo::CollectionScan::CollectionScan(mongo::OperationContext*, mongo::Collection const*, mongo::CollectionScanParams const&amp;amp;, mongo::WorkingSet*, mongo::MatchExpression const*) 0x69) &lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;

&lt;p&gt;I heard that we have plan to make oplog special so we can do oplog traversal with global lock only. As part of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-41448&quot; title=&quot;TransactionHistoryIterator should always do untimestamped reads&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-41448&quot;&gt;&lt;del&gt;SERVER-41448&lt;/del&gt;&lt;/a&gt;, we plan to make TransactionHistoryIterator only take global IS lock. So, I am wondering is it possible to special case oplog read to not take a database or a collection lock?&lt;/p&gt;

&lt;p&gt;CC &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=siyuan.zhou&quot; class=&quot;user-hover&quot; rel=&quot;siyuan.zhou&quot;&gt;siyuan.zhou&lt;/a&gt;&lt;/p&gt;</description>
                <environment></environment>
        <key id="790600">SERVER-41558</key>
            <summary>Make CollectionScan on oplog work without holding database/collection lock</summary>
                <type id="6" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Question</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="3">Duplicate</resolution>
                                        <assignee username="backlog-server-execution">Backlog - Storage Execution Team</assignee>
                                    <reporter username="lingzhi.deng@mongodb.com">Lingzhi Deng</reporter>
                        <labels>
                    </labels>
                <created>Wed, 5 Jun 2019 22:43:41 +0000</created>
                <updated>Tue, 6 Dec 2022 02:57:41 +0000</updated>
                            <resolved>Fri, 7 Jun 2019 14:37:17 +0000</resolved>
                                                                    <component>Storage</component>
                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="2275771" author="milkie" created="Fri, 7 Jun 2019 14:37:17 +0000"  >&lt;p&gt;The linked ticket will be solving this issue.&lt;/p&gt;</comment>
                            <comment id="2273656" author="milkie" created="Thu, 6 Jun 2019 12:14:54 +0000"  >&lt;p&gt;Yes, I think that would be reasonable to make an exception on the locking requirements for local.oplog.rs namespace.&lt;/p&gt;</comment>
                            <comment id="2273304" author="siyuan.zhou@10gen.com" created="Wed, 5 Jun 2019 22:49:43 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=milkie&quot; class=&quot;user-hover&quot; rel=&quot;milkie&quot;&gt;milkie&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=benety.goh&quot; class=&quot;user-hover&quot; rel=&quot;benety.goh&quot;&gt;benety.goh&lt;/a&gt;, we tried to use the oplog collection pointer from LocalOplogInfo for oplog reading while only holding global lock IS lock, but it seems DatabaseHolderImpl checks for DB lock. Does it make sense to make an exception for oplog here?&lt;/p&gt;</comment>
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