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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>[CXX-2414] Ignore read preference for $out/$merge on secondaries if any servers are pre-5.0</title>
                <link>https://jira.mongodb.org/browse/CXX-2414</link>
                <project id="11980" key="CXX">C++ Driver</project>
                    <description>&lt;p&gt;This ticket was split from &lt;a href=&quot;https://jira.mongodb.org/browse/DRIVERS-1969&quot; title=&quot;Ignore read preference for $out/$merge on secondaries if any servers are pre-5.0&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DRIVERS-1969&quot;&gt;&lt;del&gt;DRIVERS-1969&lt;/del&gt;&lt;/a&gt;, please see that ticket for a detailed description.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1920646">CXX-2414</key>
            <summary>Ignore read preference for $out/$merge on secondaries if any servers are pre-5.0</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="13202">Works as Designed</resolution>
                                        <assignee username="jesse.williamson@mongodb.com">Jesse Williamson</assignee>
                                    <reporter username="dbeng-pm-bot">PM Bot</reporter>
                        <labels>
                    </labels>
                <created>Mon, 8 Nov 2021 17:59:14 +0000</created>
                <updated>Fri, 27 Oct 2023 13:13:32 +0000</updated>
                            <resolved>Tue, 22 Mar 2022 21:05:59 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="4428133" author="JIRAUSER1261121" created="Tue, 22 Mar 2022 21:05:59 +0000"  >&lt;p&gt;This depends on the wire protocol version and resultant sever selection negotiated by the underlying /connection/-- which are the C driver&apos;s responsibility. In the few C++ driver tests that reference readPreference, it&apos;s being read.&lt;/p&gt;</comment>
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                                                                <inwardlinks description="split from">
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            <issuekey id="1913549">DRIVERS-1969</issuekey>
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                        <customfieldname>Upstream Changes Summary</customfieldname>
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                            <customfieldvalue>&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/browse/DRIVERS-1969&quot; title=&quot;Ignore read preference for $out/$merge on secondaries if any servers are pre-5.0&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DRIVERS-1969&quot;&gt;&lt;del&gt;DRIVERS-1969&lt;/del&gt;&lt;/a&gt;:&lt;br/&gt;
In &lt;a href=&quot;https://github.com/mongodb/specifications/commit/747b7480c47900827ff2b64f23c2a14636803d1a&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;mongodb/specifications@747b748&lt;/a&gt;, the rules were applying a read preference for aggregations using &lt;tt&gt;$out&lt;/tt&gt; and &lt;tt&gt;$merge&lt;/tt&gt; was changed. Previously, drivers were instructed to attempt using the read preference and only fall back to a primary if a pre-5.0 secondary was selected.&lt;/p&gt;

&lt;p&gt;This was changed to require drivers to always disregard the read preference if there is &lt;em&gt;any&lt;/em&gt; evidence of a pre-5.0 server. If there are either no available servers or all servers are 5.0+ (or load balanced, where we assume 5.0+), drivers can utilize the read preference.&lt;/p&gt;

&lt;p&gt;Spec tests have not been changed, as this clarification really only changes behavior for mixed version clusters or a replica set consisting of a single pre-5.0 primary, neither of which are tested.&lt;/p&gt;</customfieldvalue>

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