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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-45845] TransactionCoordinator stepUp can deadlock</title>
                <link>https://jira.mongodb.org/browse/SERVER-45845</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Scenario:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;a transaction on ns foo.bar is on prepare&lt;/li&gt;
	&lt;li&gt;new primary just stepped up on this shard&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;Sequence of events to deadlock:&lt;br/&gt;
1. The new primary&apos;s TransactionParticipants make sure necessary locks are acquired for the prepared txn.&lt;br/&gt;
2. An operation makes a write, generating a new oplog and advancing last op timestamp.&lt;br/&gt;
3. An operation requiring a conflicting exclusive lock arrives on the new primary.&lt;br/&gt;
4. Multiple operations conflicting with the exclusive lock also arrives, blocking behind the lock request of operation in #3. The numbers came in enough to exhaust the read ticket.&lt;br/&gt;
5. TransactionCoordinatorService stepUp code kicks in, &lt;a href=&quot;https://github.com/mongodb/mongo/blob/r4.3.2/src/mongo/db/s/transaction_coordinator_service.cpp#L191&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;tries to wait for last op to become majority committed&lt;/a&gt;.&lt;br/&gt;
6. Secondaries try to fetch oplog from new primary but can&apos;t query the primary because the read ticket is already exhausted. So majority timestamp won&apos;t advance.&lt;br/&gt;
7. Retried CoordinatorCommit command for the prepared transaction arrives &lt;a href=&quot;https://github.com/mongodb/mongo/blob/r4.3.2/src/mongo/db/s/transaction_coordinator_catalog.cpp#L117&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;tries to wait for TransactionCoordinatorService to fully step up before proceeding&lt;/a&gt;. Deadlock occurs. Also note that TransactionCoordinatorService will also try to &lt;a href=&quot;https://github.com/mongodb/mongo/blob/r4.3.2/src/mongo/db/s/transaction_coordinator_service.cpp#L224&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;start coordinating in progress coordinators after waiting for majority&lt;/a&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1120474">SERVER-45845</key>
            <summary>TransactionCoordinator stepUp can deadlock</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="3">Duplicate</resolution>
                                        <assignee username="backlog-server-sharding">[DO NOT USE] Backlog - Sharding Team</assignee>
                                    <reporter username="randolph@mongodb.com">Randolph Tan</reporter>
                        <labels>
                    </labels>
                <created>Wed, 29 Jan 2020 18:38:45 +0000</created>
                <updated>Tue, 6 Dec 2022 02:37:04 +0000</updated>
                            <resolved>Wed, 19 Feb 2020 22:52:12 +0000</resolved>
                                                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="2885776" author="esha.maharishi@10gen.com" created="Wed, 19 Feb 2020 22:51:56 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=renctan&quot; class=&quot;user-hover&quot; rel=&quot;renctan&quot;&gt;renctan&lt;/a&gt; ok, closing as dup of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-45953&quot; title=&quot;Exempt oplog readers from acquiring read tickets&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-45953&quot;&gt;&lt;del&gt;SERVER-45953&lt;/del&gt;&lt;/a&gt;. If you think we shouldn&apos;t do that for any reason, please do reopen this ticket. &lt;img class=&quot;emoticon&quot; src=&quot;https://jira.mongodb.org/images/icons/emoticons/smile.png&quot; height=&quot;16&quot; width=&quot;16&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt;&lt;/p&gt;</comment>
                            <comment id="2885436" author="renctan" created="Wed, 19 Feb 2020 20:17:48 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=esha.maharishi&quot; class=&quot;user-hover&quot; rel=&quot;esha.maharishi&quot;&gt;esha.maharishi&lt;/a&gt; I believe fixing &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-45953&quot; title=&quot;Exempt oplog readers from acquiring read tickets&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-45953&quot;&gt;&lt;del&gt;SERVER-45953&lt;/del&gt;&lt;/a&gt; will break the cyclic dependency in the deadlock chain.&lt;/p&gt;</comment>
                            <comment id="2878570" author="esha.maharishi@10gen.com" created="Fri, 14 Feb 2020 16:08:03 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=renctan&quot; class=&quot;user-hover&quot; rel=&quot;renctan&quot;&gt;renctan&lt;/a&gt;, is there work to do after &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-45953&quot; title=&quot;Exempt oplog readers from acquiring read tickets&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-45953&quot;&gt;&lt;del&gt;SERVER-45953&lt;/del&gt;&lt;/a&gt;?&lt;/p&gt;</comment>
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