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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-14885] replica sets that disable chaining may have trouble electing a primary if members have different priorities</title>
                <link>https://jira.mongodb.org/browse/SERVER-14885</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;This report comes mostly from code inspection. When chaining is not allowed in replication, ReplSetImpl::getMemberToSyncTo only allows a secondary to sync from the primary. If a primary cannot be reached, syncing does not happen.&lt;/p&gt;

&lt;p&gt;In consensus.cpp, an election will refuse to elect a member with a lower priority if a member with a higher priority exists and is within 10 seconds of being caught up.&lt;/p&gt;

&lt;p&gt;These two facts together can cause a replica set to never elect a primary.&lt;/p&gt;

&lt;p&gt;Take the following scenario. Chaining is disabled, and no primary exists. Member A has priority 10 (the highest in the set), and is 5 seconds behind member B that has priority 1. B is furthest along. Neither A nor B will ever be elected. B won&apos;t be elected because the election algorithm will say &quot;A is within 10 seconds and has a higher priority&quot;. A won&apos;t get elected because it is behind B, and because chaining is disallowed, cannot replicate from B to catch up.&lt;/p&gt;

&lt;p&gt;I think the end result is a primary never gets elected.&lt;/p&gt;

&lt;p&gt;I don&apos;t see any code that says &quot;ignore the chainingAllowed bit and replicate off a secondary because a primary does not exist&quot;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="152410">SERVER-14885</key>
            <summary>replica sets that disable chaining may have trouble electing a primary if members have different priorities</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="backlog-server-repl">Backlog - Replication Team</assignee>
                                    <reporter username="zardosht">Zardosht Kasheff</reporter>
                        <labels>
                            <label>elections</label>
                            <label>mms-s</label>
                    </labels>
                <created>Wed, 13 Aug 2014 16:09:42 +0000</created>
                <updated>Tue, 6 Dec 2022 05:02:46 +0000</updated>
                            <resolved>Mon, 26 Oct 2015 19:18:51 +0000</resolved>
                                                    <fixVersion>3.1.9</fixVersion>
                                    <component>Replication</component>
                                        <votes>0</votes>
                                    <watches>15</watches>
                                                                                                                <comments>
                            <comment id="1070766" author="milkie" created="Mon, 26 Oct 2015 19:18:51 +0000"  >&lt;p&gt;In 3.1.9, the new election protocol no longer has this problem.  Priorities are handled in a new way.&lt;/p&gt;</comment>
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