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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-56254] [SBE] ixscan&apos;s snapshot id slot should be updated during yield recovery</title>
                <link>https://jira.mongodb.org/browse/SERVER-56254</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;In &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-52907&quot; title=&quot;Implement index key consistency check in SBE FETCH&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-52907&quot;&gt;&lt;del&gt;SERVER-52907&lt;/del&gt;&lt;/a&gt;, we extended the SBE ixscan stage to have a slot for the snapshot id. The snapshot id slot is currently only &lt;a href=&quot;https://github.com/mongodb/mongo/blob/78c15ec274d0a4162aa5fcb29b367a8e1c0809d3/src/mongo/db/exec/sbe/stages/ix_scan.cpp#L131-L135&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;reset during IndexScanStage::prepare()&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;When performing a fetch, the seek stage will &lt;a href=&quot;https://github.com/mongodb/mongo/blob/78c15ec274d0a4162aa5fcb29b367a8e1c0809d3/src/mongo/db/query/sbe_stage_builder.cpp#L309&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;consult the value of this slot&lt;/a&gt; in order to determine whether the index key may have survived a yield. If the snapshot id associated with the index key is not equal to the current snapshot id, then some expensive checks are performed in order to make sure that the document being fetched still matches the query predicate.&lt;/p&gt;

&lt;p&gt;The problem is that the value of the ixscan&apos;s snapshot id slot is not updated during a yield. Imagine a long-running index scan plan which yields several times. This means that after the first yield, &lt;em&gt;all&lt;/em&gt; index keys will be associated with a stale snapshot id, and the expensive validity checks involving index key generation will be performed unnecessarily. Index key generation is known to be expensive, so this is likely to be a performance problem.&lt;/p&gt;

&lt;p&gt;In order to fix the performance problem, we should update the snapshot id held in the ixscan stage&apos;s snapshot id slot during yield recovery, i.e. during &lt;tt&gt;IndexScanStage::doRestoreState()&lt;/tt&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1686116">SERVER-56254</key>
            <summary>[SBE] ixscan&apos;s snapshot id slot should be updated during yield recovery</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="mihai.andrei@mongodb.com">Mihai Andrei</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                    </labels>
                <created>Wed, 21 Apr 2021 23:16:09 +0000</created>
                <updated>Sun, 29 Oct 2023 21:54:40 +0000</updated>
                            <resolved>Thu, 29 Apr 2021 00:47:01 +0000</resolved>
                                                    <fixVersion>5.0.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="3745580" author="xgen-internal-githook" created="Thu, 29 Apr 2021 00:05:45 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Mihai Andrei&apos;, &apos;email&apos;: &apos;mihai.andrei@10gen.com&apos;, &apos;username&apos;: &apos;mtandrei&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-56254&quot; title=&quot;[SBE] ixscan&amp;#39;s snapshot id slot should be updated during yield recovery&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-56254&quot;&gt;&lt;del&gt;SERVER-56254&lt;/del&gt;&lt;/a&gt; &lt;span class=&quot;error&quot;&gt;&amp;#91;SBE&amp;#93;&lt;/span&gt; ixscan&apos;s snapshot id slot should be updated during yield recovery&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/5891c05b1581624b0decf6663bd6b354161b2cb6&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/5891c05b1581624b0decf6663bd6b354161b2cb6&lt;/a&gt;&lt;/p&gt;</comment>
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