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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-41187] Majority committed replication lag spikes after an election</title>
                <link>https://jira.mongodb.org/browse/SERVER-41187</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;One of my scripts for testing Flow Control prompts an election. I&apos;ve noticed that in some runs of the test, there is a spike in reported lastCommitted lag that occurs immediately after the election. This spike occurred both when the election chose the same primary as previously and when the election chose a different node as primary. Flow Control is a consumer of lastCommitted lag, so it will respond to the spike and throttle writes. I don&apos;t see why lastCommitted lag should have a reason to spike, particularly if the same primary is elected, so I believe this behavior should be investigated.&lt;/p&gt;</description>
                <environment></environment>
        <key id="770018">SERVER-41187</key>
            <summary>Majority committed replication lag spikes after an election</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="9">Done</resolution>
                                        <assignee username="lingzhi.deng@mongodb.com">Lingzhi Deng</assignee>
                                    <reporter username="maria.vankeulen@mongodb.com">Maria van Keulen</reporter>
                        <labels>
                    </labels>
                <created>Thu, 16 May 2019 19:06:36 +0000</created>
                <updated>Thu, 14 Nov 2019 21:11:29 +0000</updated>
                            <resolved>Thu, 14 Nov 2019 21:11:29 +0000</resolved>
                                                                    <component>Replication</component>
                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="2541521" author="lingzhi.deng" created="Thu, 14 Nov 2019 21:11:29 +0000"  >&lt;p&gt;Closing as the investigation is done. We can continue the conversation in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44634&quot; title=&quot;Account for election down time when calculating majority committed lag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44634&quot;&gt;&lt;del&gt;SERVER-44634&lt;/del&gt;&lt;/a&gt; instead.&lt;/p&gt;</comment>
                            <comment id="2541496" author="maria.vankeulen" created="Thu, 14 Nov 2019 20:59:11 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=lingzhi.deng&quot; class=&quot;user-hover&quot; rel=&quot;lingzhi.deng&quot;&gt;lingzhi.deng&lt;/a&gt; and I discussed this lag overstatement issue further today, and I&apos;ve filed &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44634&quot; title=&quot;Account for election down time when calculating majority committed lag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44634&quot;&gt;&lt;del&gt;SERVER-44634&lt;/del&gt;&lt;/a&gt; to track the fix. I think it&apos;s fair to focus on when it occurs due to elections rather than when it occurs due to the replica set being idle for extended periods, since elections are a more discernible case.&lt;/p&gt;</comment>
                            <comment id="2255019" author="maria.vankeulen" created="Tue, 21 May 2019 20:42:38 +0000"  >&lt;p&gt;My hypothesis is that when the new primary starts accepting writes, there is a brief window of time during which some of the secondaries have not established their new sync source yet, so they are not replicating. Here is a screenshot of FTDC data from a script that forces an election of the same primary and generates majority committed lag. Node 0 is the primary, Nodes 1 through 3 are periodically stopped to induce replication lag, and Node 4 is allowed to replicate writes as normal. &lt;br/&gt;
 &lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;a id=&quot;217593_thumb&quot; href=&quot;https://jira.mongodb.org/secure/attachment/217593/217593_Screen+Shot+2019-05-21+at+4.31.03+PM.png&quot; title=&quot;Screen Shot 2019-05-21 at 4.31.03 PM.png&quot; file-preview-type=&quot;image&quot; file-preview-id=&quot;217593&quot; file-preview-title=&quot;Screen Shot 2019-05-21 at 4.31.03 PM.png&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/thumbnail/217593/_thumb_217593.png&quot; style=&quot;border: 0px solid black&quot; role=&quot;presentation&quot;/&gt;&lt;/a&gt;&lt;/span&gt; &lt;br/&gt;
 In the interval between B and C, the primary is accepting writes, but Node 4 has not yet re-established Node 0 as its sync source, as evidenced by the gap in the FTDC data for syncSourceId. The lastCommitted lag spikes in this interval. I am sending this to Replication to investigate further.&lt;/p&gt;</comment>
                            <comment id="2249380" author="maria.vankeulen" created="Thu, 16 May 2019 19:09:12 +0000"  >&lt;p&gt;This may be related to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-32703&quot; title=&quot;Secondary can take a couple minutes to re-establish sync source after network partition&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-32703&quot;&gt;&lt;del&gt;SERVER-32703&lt;/del&gt;&lt;/a&gt;. I did notice that in the runs of my test case that had these lag spikes, several secondaries were missing syncSourceId data in FTDC.&lt;/p&gt;</comment>
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