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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>[DOCS-15441] Investigate changes in REP-784: PrimaryPreferred read preference on the destination can lead to regressing state</title>
                <link>https://jira.mongodb.org/browse/DOCS-15441</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>    &lt;div class=&quot;panel&quot; style=&quot;background-color: #c2d2c2;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;background-color: #239eb0;&quot;&gt;&lt;b&gt;Original Downstream Change Summary&lt;/b&gt;&lt;/div&gt;&lt;/div&gt;
&lt;p&gt;    We modified the way we handle read preference in mongosync:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;On the source, we respect whatever the user requested and use PrimaryPreferred if they did not set any preference.&lt;/li&gt;
	&lt;li&gt;On the destination, we overwrite whatever the user requested with Primary.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;If the user reverses the replication direction, we will apply the same logic on the new source and new destination.&lt;/p&gt;

&lt;p&gt;e.g.&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;User asks for nearest on source and secondaryPreferred on destination.&lt;/li&gt;
	&lt;li&gt;We will use nearest on source (as requested) and Primary on destination (overwritten).&lt;/li&gt;
	&lt;li&gt;If they call Reverse, we will use secondaryPreferred on the new source (as requested) and Primary on new destination (overwritten).
&lt;h2&gt;&lt;a name=&quot;DescriptionofLinkedTicket&quot;&gt;&lt;/a&gt;Description of Linked Ticket&lt;/h2&gt;
&lt;p&gt;    The following scenario is possible:&lt;br/&gt;
1. a. Replicator persists state on destination as COMMITTING&lt;br/&gt;
1. b. State COMMITTING is saved on majority of nodes, but not some secondary S, which still thinks the state is RUNNING.&lt;br/&gt;
2. Replicator is killed.&lt;br/&gt;
3. Replicator restarts, and tries to restore its resume data. Since it uses PrimaryPreferred, if the primary is unavailable the replicator may read from S, and restore its state as RUNNING.&lt;/p&gt;&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;We may also see similar issues whenever we hit the api/v1/progress endpoint: it may return stale data.&lt;/p&gt;

&lt;p&gt;To solve this, we should:&lt;br/&gt;
1. Force destination readPreference to be primary&lt;br/&gt;
2. Recreate mongo clients on reverse (since the destination should have the readPreference set)&lt;/p&gt;

&lt;p&gt;Moved part on linearizability to &lt;a href=&quot;https://jira.mongodb.org/browse/REP-854&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;https://jira.mongodb.org/browse/REP-854&lt;/a&gt;&lt;/p&gt;
</description>
                <environment></environment>
        <key id="2075561">DOCS-15441</key>
            <summary>Investigate changes in REP-784: PrimaryPreferred read preference on the destination can lead to regressing state</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="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="-1">Unassigned</assignee>
                                    <reporter username="backlog-server-pm">Backlog - Core Eng Program Management Team</reporter>
                        <labels>
                            <label>backlog</label>
                            <label>request</label>
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                <created>Thu, 23 Jun 2022 19:23:39 +0000</created>
                <updated>Mon, 22 Jan 2024 16:09:15 +0000</updated>
                                                            <fixVersion>1.0.0</fixVersion>
                                    <component>C2C</component>
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                    <component>Server</component>
                        <due></due>
                            <votes>0</votes>
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