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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-78764] Revisit sampling CE scan-from-start in performance variants</title>
                <link>https://jira.mongodb.org/browse/SERVER-78764</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;In order to reduce noise in sampling variants, we opted to scan from the start of the collection (rather than taking a true random sample) in our performance tests. We should revisit this approach.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2385760">SERVER-78764</key>
            <summary>Revisit sampling CE scan-from-start in performance variants</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="2">Won&apos;t Fix</resolution>
                                        <assignee username="backlog-query-optimization">Backlog - Query Optimization</assignee>
                                    <reporter username="alya.berciu@mongodb.com">Alya Berciu</reporter>
                        <labels>
                    </labels>
                <created>Fri, 7 Jul 2023 09:18:43 +0000</created>
                <updated>Fri, 19 Jan 2024 16:51:33 +0000</updated>
                            <resolved>Fri, 19 Jan 2024 16:48:21 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="6026124" author="david.percy" created="Fri, 19 Jan 2024 16:48:22 +0000"  >&lt;p&gt;It sounds like when we set up these tests, we had decided to use sequential sampling because:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;We want to minimize noise in the tests, and saw that random sampling made them noisier.&lt;/li&gt;
	&lt;li&gt;Given that the test data is random (with no correlation between value and position), the estimates we get from sequential sampling vs random sampling will be similar.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;We considered doing random sampling with a fixed seed, but it uses a WiredTiger random cursor, which doesn&apos;t support repeatability / fixed seed: &lt;a href=&quot;https://jira.mongodb.org/browse/WT-11815&quot; title=&quot;Implement repeatable random cursor&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-11815&quot;&gt;WT-11815&lt;/a&gt;.&#160; (And repeatability requires more than a fixed seed, because the result also depends on the tree shape for example.)&lt;/p&gt;</comment>
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