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    <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-50710] Lock acquired in FindCmd run() method is not yielded by SBE</title>
                <link>https://jira.mongodb.org/browse/SERVER-50710</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The &lt;tt&gt;FindCmd&lt;/tt&gt; currently acquires an &lt;tt&gt;AutoGetCollectionForReadCommand&lt;/tt&gt; early in its code path:&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/a8bf9e88b3cd2c0036b3ae3e484dbbc933fc4614/src/mongo/db/commands/find_cmd.cpp#L359-L362&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/a8bf9e88b3cd2c0036b3ae3e484dbbc933fc4614/src/mongo/db/commands/find_cmd.cpp#L359-L362&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;This is held while constructing the &lt;tt&gt;PlanExecutor&lt;/tt&gt; via &lt;tt&gt;getExecutorFind()&lt;/tt&gt;, and it continues to be held while actually running the &lt;tt&gt;PlanExecutor&lt;/tt&gt; to produce the first batch of results. Since &lt;tt&gt;getExecutorFind()&lt;/tt&gt; may invoke runtime planning mechanism to choose a plan, query execution may occur both when calling this method and when constructing the first batch.&lt;/p&gt;

&lt;p&gt;This lock must be held for the classic query execution engine, as it uses the &lt;tt&gt;kLockExternally&lt;/tt&gt; model. This means that the caller is responsible for acquiring the necessary locks. SBE, on the other hand, uses the &lt;tt&gt;kLocksInternally&lt;/tt&gt; model. It acquires its own locks as needed. The fact that the &lt;tt&gt;FindCmd&lt;/tt&gt; also holds the lock is problematic for yielding, since the SBE yielding code has no means to relinquish this lock. As a result, not all locks held by the query are released during a yield unless that yield is happening during a getMore. This means that when the system is configured to use SBE, an operation requiring a strong lock on the collection could block for a long time behind a find command.&lt;/p&gt;

&lt;p&gt;I discovered this while attempting to adapt &lt;a href=&quot;https://github.com/mongodb/mongo/blob/a8bf9e88b3cd2c0036b3ae3e484dbbc933fc4614/jstests/noPassthrough/commands_handle_kill.js&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;commands_handle_kill.js&lt;/a&gt; to run a test case with SBE enabled. Doing so would be a good way to test that this ticket has been addressed adequately.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1460599">SERVER-50710</key>
            <summary>Lock acquired in FindCmd run() method is not yielded by SBE</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="david.storch@mongodb.com">David Storch</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                    </labels>
                <created>Wed, 2 Sep 2020 20:32:29 +0000</created>
                <updated>Sun, 29 Oct 2023 22:03:40 +0000</updated>
                            <resolved>Wed, 3 Mar 2021 04:15:26 +0000</resolved>
                                                    <fixVersion>4.9.0</fixVersion>
                                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="3643620" author="xgen-internal-githook" created="Wed, 3 Mar 2021 04:14:15 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;David Storch&apos;, &apos;email&apos;: &apos;david.storch@mongodb.com&apos;, &apos;username&apos;: &apos;dstorch&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-50710&quot; title=&quot;Lock acquired in FindCmd run() method is not yielded by SBE&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-50710&quot;&gt;&lt;del&gt;SERVER-50710&lt;/del&gt;&lt;/a&gt; Consolidate SBE and classic yielding paths&lt;/p&gt;

&lt;p&gt;SBE will now, like the classic engine, use&lt;br/&gt;
saveLockStateAndUnlock() in order to yield any locks held&lt;br/&gt;
higher on the stack.  Additionally, this patch enables the&lt;br/&gt;
&apos;concurrency&apos; suite in the SBE build variant in order to&lt;br/&gt;
provide additional yielding-related test coverage.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/f83d51c0ffe9420f8dfd68d477de228dc78f9527&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/f83d51c0ffe9420f8dfd68d477de228dc78f9527&lt;/a&gt;&lt;/p&gt;</comment>
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                                        <issuelink>
            <issuekey id="1515208">SERVER-51629</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1404486">SERVER-49385</issuekey>
        </issuelink>
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