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    <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-81909] AutoMerger&apos;s `_maxHistoryTimeCurrentRound` never updated due to variable shadowing</title>
                <link>https://jira.mongodb.org/browse/SERVER-81909</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/s/balancer/auto_merger_policy.h#L113&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;_maxHistoryTimeCurrentRound&lt;/a&gt; variable supposed to drive auto-merging scanning is never updated due to a &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/s/balancer/auto_merger_policy.cpp#L297C9-L297C20&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;variable shadowing&lt;/a&gt; that was committed involuntarily.&lt;/p&gt;

&lt;p&gt;This is not a correctness bug since it results in &quot;simply&quot; forcing the auto-merger to unnecessarily scan through chunks already inspected in previous rounds.&lt;/p&gt;

&lt;p&gt;Purpose of this ticket is to understand whether it makes sense to fix this bug or just get rid of the variable: fixing this performance bug would mean introducing a correctness bug since the auto-merger would skip scanning chunks that were split without being migrated. The side effect would be produced by &lt;a href=&quot;https://github.com/mongodb/mongo/blob/267c504401386922ba05ef6bfc2519dd5294dd52/src/mongo/db/s/balancer/auto_merger_policy.cpp#L307-L309&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this query&lt;/a&gt; that only returns chunks result of a migration (splits don&apos;t change &lt;tt&gt;onCurrentShardSince&lt;/tt&gt;).&lt;/p&gt;

&lt;p&gt;Other options would be:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;Force a reset of &lt;a href=&quot;https://github.com/mongodb/mongo/blob/0df6c43273e7ab340305bc9208e5775b7a591817/src/mongo/db/s/balancer/auto_merger_policy.h#L114&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;_maxHistoryTimePreviousRound&lt;/a&gt; when a split happens&lt;/li&gt;
	&lt;li&gt;Or - more fine grained - keep a &lt;tt&gt;_maxHistoryTimePreviousRound&lt;/tt&gt; per collection and just reset it for collections that undergo some split&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="2461431">SERVER-81909</key>
            <summary>AutoMerger&apos;s `_maxHistoryTimeCurrentRound` never updated due to variable shadowing</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="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-server-catalog-and-routing">Backlog - Catalog and Routing</assignee>
                                    <reporter username="pierlauro.sciarelli@mongodb.com">Pierlauro Sciarelli</reporter>
                        <labels>
                            <label>car-qw</label>
                    </labels>
                <created>Thu, 5 Oct 2023 18:58:24 +0000</created>
                <updated>Wed, 8 Nov 2023 08:53:37 +0000</updated>
                                            <version>7.2.0-rc0</version>
                    <version>7.0.2</version>
                    <version>7.1.0</version>
                                                                        <votes>0</votes>
                                    <watches>1</watches>
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