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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
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        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[DOCS-12375] Document that in 4.2, an index drop will no longer kill a query which is not using the index</title>
                <link>https://jira.mongodb.org/browse/DOCS-12375</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;

&lt;p&gt;In all versions of MongoDB prior to 4.2, dropping an index on a particular collection would cause all active queries against that collection to be killed. See &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-3964&quot; title=&quot;Dropping an index invalidates all cursors on that collection, not just ones using that index.&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-3964&quot;&gt;&lt;del&gt;SERVER-3964&lt;/del&gt;&lt;/a&gt;. Work done by the query team&apos;s &quot;all cursors globally managed&quot; project has improved this behavior such that dropping an index only kills concurrent queries whose plan actually relies on that index. We may wish to document this improvement (possibly as part of the 4.2 release notes?). I&apos;ve left a few additional details on &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-3964&quot; title=&quot;Dropping an index invalidates all cursors on that collection, not just ones using that index.&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-3964&quot;&gt;&lt;del&gt;SERVER-3964&lt;/del&gt;&lt;/a&gt;, but feel free to reach out directly to me if you have any questions or require additional information.&lt;/p&gt;
&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;
&lt;ul&gt;
	&lt;li&gt;Update &lt;a href=&quot;https://docs.mongodb.com/manual/reference/command/dropIndexes/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;dropIndexes&lt;/a&gt; and its shell helper with the new behavior&lt;/li&gt;
	&lt;li&gt;Update the release note with the new behavior&lt;/li&gt;
&lt;/ul&gt;


&lt;h2&gt;&lt;a name=&quot;%C2%A0&quot;&gt;&lt;/a&gt;&#160;&lt;/h2&gt;</description>
                <environment></environment>
        <key id="674103">DOCS-12375</key>
            <summary>Document that in 4.2, an index drop will no longer kill a query which is not using the index</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="13201">Fixed</resolution>
                                        <assignee username="ravind.kumar">Ravind Kumar</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                            <label>docs-query</label>
                    </labels>
                <created>Thu, 17 Jan 2019 15:03:38 +0000</created>
                <updated>Mon, 30 Oct 2023 20:47:52 +0000</updated>
                            <resolved>Fri, 1 Mar 2019 14:49:12 +0000</resolved>
                                                    <fixVersion>Server_Docs_20231030</fixVersion>
                                    <component>manual</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="2167336" author="xgen-internal-githook" created="Fri, 1 Mar 2019 14:49:06 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;rk-mongo&apos;, &apos;email&apos;: &apos;ravind.kumar@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12375&quot; title=&quot;Document that in 4.2, an index drop will no longer kill a query which is not using the index&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12375&quot;&gt;&lt;del&gt;DOCS-12375&lt;/del&gt;&lt;/a&gt;: dropIndexes only kills queries using dropped index&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/c21ea8329a2c7bc68c98be342de6ab4b08b106a6&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/c21ea8329a2c7bc68c98be342de6ab4b08b106a6&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2122908" author="david.storch" created="Tue, 22 Jan 2019 16:54:27 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=ravind.kumar&quot; class=&quot;user-hover&quot; rel=&quot;ravind.kumar&quot;&gt;ravind.kumar&lt;/a&gt;, actually, I looked more thoroughly at the source code, and it appears that my previous comment was incorrect! Apparently the dropIndexes command does take a MODE_X lock on the entire database, rather than taking a MODE_IX lock on the database and a MODE_X lock on the collection. Therefore, the docs would be correct in asserting that &lt;tt&gt;dropIndexes&lt;/tt&gt; write locks the entire database.&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=geert.bosch&quot; class=&quot;user-hover&quot; rel=&quot;geert.bosch&quot;&gt;geert.bosch&lt;/a&gt; could confirm my reading of the code. Also, he is working on a project to take more granular locks for catalog operations (PM-1242), so he may be changing this soon. Either way, &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-3964&quot; title=&quot;Dropping an index invalidates all cursors on that collection, not just ones using that index.&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-3964&quot;&gt;&lt;del&gt;SERVER-3964&lt;/del&gt;&lt;/a&gt; did not change any locking behavior, so this conversation does not pertain to the particular documentation requested by this ticket.&lt;/p&gt;</comment>
                            <comment id="2120296" author="ravind.kumar" created="Fri, 18 Jan 2019 14:56:13 +0000"  >&lt;p&gt;Thanks David - the current docs simply state that the command write locks the whole database, which does not seem correct. might as well fix that while I&apos;m in there.&lt;/p&gt;

&lt;p&gt;Is the locking behavior you&apos;re describing generally true for 3.6+? I know we&apos;re slightly out of scope here but it was bothering me while reading through the current docs.&lt;/p&gt;</comment>
                            <comment id="2120269" author="david.storch" created="Fri, 18 Jan 2019 14:26:13 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=ravind.kumar&quot; class=&quot;user-hover&quot; rel=&quot;ravind.kumar&quot;&gt;ravind.kumar&lt;/a&gt;, the locking behavior of index drops did not change for this project. An index drop operation will take an exclusive lock on the &lt;em&gt;collection&lt;/em&gt; not the database. Specifically, it will acquire a MODE_IX (&quot;intent exclusive&quot;) global lock, a MODE_IX lock at the database level, and a MODE_X (exclusive) lock on the collection. The MODE_X collection lock will exclude all other readers and writers from the collection. However, the MODE_IX database lock will permit concurrent readers and writers in other collections.&lt;/p&gt;</comment>
                            <comment id="2118274" author="ravind.kumar" created="Thu, 17 Jan 2019 15:40:52 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=david.storch&quot; class=&quot;user-hover&quot; rel=&quot;david.storch&quot;&gt;david.storch&lt;/a&gt; - from reading the epic for global cursors, there are changes to locking behavior. Right now we document that dropping an index take a write lock on the database. Is that still the case?&lt;/p&gt;</comment>
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