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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-30843] Use std::set::upper_bound when calculating the stable timestamp</title>
                <link>https://jira.mongodb.org/browse/SERVER-30843</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Currently the function &lt;tt&gt;ReplicationCoordinatorImpl::_calculateStableTimestamp&lt;/tt&gt; uses &lt;tt&gt;std::find_if&lt;/tt&gt; to search through the list of stable timestamp candidates. The list of stable timestamp candidates is maintained in sorted order, since it is a &lt;tt&gt;std::set&lt;/tt&gt;, however, &lt;tt&gt;std::find_if&lt;/tt&gt; doesn&apos;t take advantage of this. Thus, it&apos;s performance is linear in the size of the candidates list, and becomes the slowest part of the &lt;tt&gt;set stableTimestampForStorage&lt;/tt&gt; operation if the candidate list grows to some non-trivial size. &lt;/p&gt;

&lt;p&gt;We can optimize this by using the &lt;tt&gt;std::set::upper_bound&lt;/tt&gt; function to calculate the stable timestamp. For a &lt;tt&gt;std::set&lt;/tt&gt; container, &lt;tt&gt;upper_bound&lt;/tt&gt; has logarithmic complexity, and returns the first element in a sorted range that is greater than some given value. If we do something like  &lt;/p&gt;

&lt;p/&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;candidates.upper_bound(commitPoint)&lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;

&lt;p&gt;we can obtain an iterator to the &lt;em&gt;smallest candidate timestamp that is greater than the commit point&lt;/em&gt;. By decrementing this iterator by 1, we can then obtain the greatest timestamp candidate that is less than or equal to the commit point. (This is the basic concept; there are a few edge cases to handle). &lt;/p&gt;

&lt;p&gt;This should be done to address the performance regressions introduced by &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-29891&quot; title=&quot;Roll Back to Checkpoint: Call setStableTimestamp() when commit point or last applied changes&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-29891&quot;&gt;&lt;del&gt;SERVER-29891&lt;/del&gt;&lt;/a&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="420430">SERVER-30843</key>
            <summary>Use std::set::upper_bound when calculating the stable timestamp</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="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="william.schultz@mongodb.com">William Schultz</assignee>
                                    <reporter username="william.schultz@mongodb.com">William Schultz</reporter>
                        <labels>
                    </labels>
                <created>Fri, 25 Aug 2017 18:39:11 +0000</created>
                <updated>Mon, 30 Oct 2023 23:14:01 +0000</updated>
                            <resolved>Tue, 12 Sep 2017 22:42:35 +0000</resolved>
                                                    <fixVersion>3.6.0-rc0</fixVersion>
                                    <component>Replication</component>
                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="1671373" author="ramon.fernandez" created="Tue, 12 Sep 2017 23:11:34 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: u&apos;will62794&apos;, &apos;name&apos;: u&apos;William Schultz&apos;, &apos;email&apos;: u&apos;william.schultz@mongodb.com&apos;}
&lt;p&gt;Message:&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-30843&quot; title=&quot;Use std::set::upper_bound when calculating the stable timestamp&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-30843&quot;&gt;&lt;del&gt;SERVER-30843&lt;/del&gt;&lt;/a&gt; Use std::set::upper_bound to calculate the stable timestamp&lt;br/&gt;
Branch:master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/bf8ae1b3edbf7470e92b7407f76a042cc2246d48&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/bf8ae1b3edbf7470e92b7407f76a042cc2246d48&lt;/a&gt;&lt;/p&gt;</comment>
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            <issuekey id="398977">SERVER-29891</issuekey>
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            <issuekey id="420445">SERVER-30845</issuekey>
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