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    <title>MongoDB Jira</title>
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    <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-29534] the unaligned variables in counter.h contribute to high use contention</title>
                <link>https://jira.mongodb.org/browse/SERVER-29534</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;In counters.h, the variables with types AtomicUInt32 and AtomicInt64 need to be cache line aligned. as the comment says, &quot;there will be a lot of cache line contention on these.&quot; false sharing  with these counters creates significant contention when loads are high.&lt;/p&gt;</description>
                <environment></environment>
        <key id="392135">SERVER-29534</key>
            <summary>the unaligned variables in counter.h contribute to high use contention</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="andrew.morrow@mongodb.com">Andrew Morrow</assignee>
                                    <reporter username="jvf">Jim Van Fleet</reporter>
                        <labels>
                    </labels>
                <created>Fri, 9 Jun 2017 14:59:20 +0000</created>
                <updated>Mon, 30 Oct 2023 23:16:13 +0000</updated>
                            <resolved>Fri, 7 Jul 2017 15:48:50 +0000</resolved>
                                                    <fixVersion>3.5.10</fixVersion>
                                    <component>Internal Code</component>
                                        <votes>0</votes>
                                    <watches>10</watches>
                                                                                                                <comments>
                            <comment id="1616380" author="xgen-internal-githook" created="Fri, 7 Jul 2017 15:47:01 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;acmorrow&apos;, u&apos;name&apos;: u&apos;Andrew Morrow&apos;, u&apos;email&apos;: u&apos;acm@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-29534&quot; title=&quot;the unaligned variables in counter.h contribute to high use contention&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-29534&quot;&gt;&lt;del&gt;SERVER-29534&lt;/del&gt;&lt;/a&gt; Place network and op counters on independent cache lines&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/be4c4f1fffe6ca69fb67ee872b52b3bd4e630659&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/be4c4f1fffe6ca69fb67ee872b52b3bd4e630659&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1608022" author="jvf" created="Tue, 27 Jun 2017 20:12:57 +0000"  >&lt;p&gt;I can not say I have tested the changes directly, but I have run a number of experiments with the changed code. None of the tests showed negative leanings.&lt;/p&gt;

&lt;p&gt;The test that prompted this change is not available to me at this time, so I am disappointed in not being able to provide that feedback..&lt;/p&gt;</comment>
                            <comment id="1600079" author="acm" created="Sat, 17 Jun 2017 21:48:57 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=jvf&quot; class=&quot;user-hover&quot; rel=&quot;jvf&quot;&gt;jvf&lt;/a&gt; - &lt;/p&gt;

&lt;p&gt;Could you please re-run your experiment that indicated false sharing on these counters with the following branch:&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/acmorrow/mongo/commits/partition-no-false-sharing&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/acmorrow/mongo/commits/partition-no-false-sharing&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;Note that this branch also spaces out the striped locks in the cursor manager lock partition, so I think it might be interesting to see if you can find any increased throughput or reduced cache ping-ponging with this branch on whatever workload you were using to look at the scalability in that component.&lt;/p&gt;

&lt;p&gt;If possible, I recommend you A/B testing this against the prior commit on that branch, so we aren&apos;t comparing apples to oranges - there have been a lot of other changes committed on master recently.&lt;/p&gt;</comment>
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