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    <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-77864] Make the use of the AlternativeClientRegion for replay protection implicit</title>
                <link>https://jira.mongodb.org/browse/SERVER-77864</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;In order to guarantee replay protection many command such as ShardsvrParticipantBlock will run within a&lt;br/&gt;
retryable write. Any local transaction or retryable write spawned by this command&lt;br/&gt;
(such as the release of the critical section) using the original operation context&lt;br/&gt;
will cause a dead lock due to the session used that has been already checked-out. We prevent the issue by using a &lt;a href=&quot;https://github.com/10gen/mongo/blob/911bf4f087168bffce30bcaecbca4c1129a055a0/src/mongo/db/s/shardsvr_participant_block_command.cpp#L129-L137&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;new operation context with an empty session&lt;/a&gt; and later by issuing a dummy write to&#160; &lt;a href=&quot;https://github.com/10gen/mongo/blob/911bf4f087168bffce30bcaecbca4c1129a055a0/src/mongo/db/s/shardsvr_participant_block_command.cpp#L148-L153&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;durably persist the session in the oplog&lt;/a&gt;.&#160;&lt;/p&gt;

&lt;p&gt;This is ok since the only reason we use a retryable write is indeed to guarantee replay protection, which is a situation in which a DDL is retried by a node that is no longer the primary (this can happen because of a network partition). By storing session information in the oplog, any request coming with a txnNumber lower then the persisted one will result in an error, preventing the old primary to successfully commit.&lt;/p&gt;

&lt;p&gt;At the moment there is no better solution unless we re-think a way to guarantee replay protection without forcing those commands to run within a retryable write.&#160;&lt;/p&gt;

&lt;p&gt;The goal of the ticket is to simplify the readability of and re-usage of the boilerplate code that prevents the deadlock. We could do this by hiding the code in a RAII object helper class or by executing it from the entry point (this might require some design).&lt;/p&gt;</description>
                <environment></environment>
        <key id="2360894">SERVER-77864</key>
            <summary>Make the use of the AlternativeClientRegion for replay protection implicit</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="backlog-server-catalog-and-routing">Backlog - Catalog and Routing</assignee>
                                    <reporter username="enrico.golfieri@mongodb.com">Enrico Golfieri</reporter>
                        <labels>
                            <label>oldshardingemea</label>
                            <label>shardingemea-qw</label>
                    </labels>
                <created>Wed, 7 Jun 2023 09:02:13 +0000</created>
                <updated>Thu, 26 Oct 2023 10:09:57 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>2</watches>
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