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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-47006] Implement a downgrade floor between 4.4 and 4.2</title>
                <link>https://jira.mongodb.org/browse/SERVER-47006</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;We have realized that we need a downgrade floor, because it&apos;s possible that multi-shard multi-document transactions will generate data that existing versions of MongoDB 4.2 won&apos;t be able to read.&lt;/p&gt;

&lt;p&gt;We are planning to increment the WiredTiger compatibility version in MongoDB 4.2 from 3.2.2 to 3.3.0 in &lt;a href=&quot;https://jira.mongodb.org/browse/WT-5892&quot; title=&quot;Bump log/WT version to facilitate downgrade floor for MongoDB 4.2&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-5892&quot;&gt;&lt;del&gt;WT-5892&lt;/del&gt;&lt;/a&gt;. In order for the downgrade floor to work we need MongoDB to also set some specific compatibility version strings in &lt;tt&gt;wiredtiger_open&lt;/tt&gt;.&lt;/p&gt;

&lt;p&gt;We need to set &lt;tt&gt;compatibility=(release=3.2)&lt;/tt&gt; to make sure that MongoDB 4.2 keeps producing log files in a format that older releases understand.&lt;/p&gt;

&lt;p&gt;We need to set &lt;tt&gt;compatibility=(requires_max=3.3)&lt;/tt&gt; to allow the 4.2 release after this change is included to open a database generated by 4.4 (after it&apos;s had a clean shutdown).&lt;/p&gt;

&lt;p&gt;There is a related but orthogonal change in &lt;a href=&quot;https://jira.mongodb.org/browse/WT-5890&quot; title=&quot;Bump log/WT version to facilitate upgrade/downgrade floor for MongoDB&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-5890&quot;&gt;&lt;del&gt;WT-5890&lt;/del&gt;&lt;/a&gt; - where we are changing it so that WiredTiger in MongoDB 4.4 will use compatibility version 10.0, and generate log files that can&apos;t be read by older versions of MongoDB. On clean shutdown the compatibility version is decreased so that it generates log files that correspond to &lt;tt&gt;compatibility=3.3&lt;/tt&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1283379">SERVER-47006</key>
            <summary>Implement a downgrade floor between 4.4 and 4.2</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="13201">Fixed</resolution>
                                        <assignee username="daniel.gottlieb@mongodb.com">Daniel Gottlieb</assignee>
                                    <reporter username="alexander.gorrod@mongodb.com">Alexander Gorrod</reporter>
                        <labels>
                    </labels>
                <created>Fri, 20 Mar 2020 04:58:40 +0000</created>
                <updated>Sun, 29 Oct 2023 22:10:31 +0000</updated>
                            <resolved>Thu, 2 Apr 2020 22:56:44 +0000</resolved>
                                                    <fixVersion>4.2.6</fixVersion>
                    <fixVersion>4.4.0-rc0</fixVersion>
                    <fixVersion>4.7.0</fixVersion>
                                    <component>Storage</component>
                                        <votes>0</votes>
                                    <watches>10</watches>
                                                                                                                <comments>
                            <comment id="3024320" author="xgen-internal-githook" created="Thu, 2 Apr 2020 22:53:48 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Daniel Gottlieb&apos;, &apos;email&apos;: &apos;daniel.gottlieb@mongodb.com&apos;, &apos;username&apos;: &apos;dgottlieb&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-47006&quot; title=&quot;Implement a downgrade floor between 4.4 and 4.2&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-47006&quot;&gt;&lt;del&gt;SERVER-47006&lt;/del&gt;&lt;/a&gt;: Implement a downgrade floor between 4.4 and 4.2 &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-47068&quot; title=&quot;Remove repair lock file when WT salvage refused to work on incompatible data files&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-47068&quot;&gt;&lt;del&gt;SERVER-47068&lt;/del&gt;&lt;/a&gt;: Remove repair lock file when WT salvage refused to work on incompatible data files.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/907fc7a809ae947f24395033027c68de9c7ae415&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/907fc7a809ae947f24395033027c68de9c7ae415&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3013756" author="xgen-internal-githook" created="Mon, 30 Mar 2020 19:58:52 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Daniel Gottlieb&apos;, &apos;email&apos;: &apos;daniel.gottlieb@mongodb.com&apos;, &apos;username&apos;: &apos;dgottlieb&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-47006&quot; title=&quot;Implement a downgrade floor between 4.4 and 4.2&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-47006&quot;&gt;&lt;del&gt;SERVER-47006&lt;/del&gt;&lt;/a&gt;: Correct a comment typo in MDB/WT versioning.&lt;br/&gt;
Branch: v4.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/eee72639cc0b1fe1e5f6877da44fbff054bd647c&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/eee72639cc0b1fe1e5f6877da44fbff054bd647c&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2995584" author="xgen-internal-githook" created="Wed, 25 Mar 2020 04:16:15 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;daniel.gottlieb@mongodb.com&apos;, &apos;name&apos;: &apos;Daniel Gottlieb&apos;, &apos;username&apos;: &apos;dgottlieb&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-47006&quot; title=&quot;Implement a downgrade floor between 4.4 and 4.2&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-47006&quot;&gt;&lt;del&gt;SERVER-47006&lt;/del&gt;&lt;/a&gt; Implement a downgrade floor between 4.4 and 4.2&lt;br/&gt;
Branch: v4.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/7300c441a25b886b9bca5e15e6be7fa7e451a85e&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/7300c441a25b886b9bca5e15e6be7fa7e451a85e&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2993672" author="xgen-internal-githook" created="Tue, 24 Mar 2020 06:17:40 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;daniel.gottlieb@mongodb.com&apos;, &apos;name&apos;: &apos;Daniel Gottlieb&apos;, &apos;username&apos;: &apos;dgottlieb&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-47006&quot; title=&quot;Implement a downgrade floor between 4.4 and 4.2&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-47006&quot;&gt;&lt;del&gt;SERVER-47006&lt;/del&gt;&lt;/a&gt; Implement a downgrade floor between 4.4 and 4.2&lt;br/&gt;
Branch: v4.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/70c19c844d348774290fdadb9f9bbb0deb5301ad&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/70c19c844d348774290fdadb9f9bbb0deb5301ad&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2991448" author="alexander.gorrod" created="Sun, 22 Mar 2020 22:25:06 +0000"  >&lt;p&gt;Thanks for the excellent write-up &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=daniel.gottlieb&quot; class=&quot;user-hover&quot; rel=&quot;daniel.gottlieb&quot;&gt;daniel.gottlieb&lt;/a&gt; - that matches the plan is a much clearer explanation than I&apos;ve been able to muster.&lt;/p&gt;</comment>
                            <comment id="2989246" author="sue.loverso" created="Fri, 20 Mar 2020 16:29:48 +0000"  >&lt;blockquote&gt;&lt;p&gt;To make sure I got this right, I&apos;ll state my interpretation/understanding (which I&apos;m extending to include 4.0 so I understand the bigger picture)&lt;/p&gt;&lt;/blockquote&gt;

&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=daniel.gottlieb&quot; class=&quot;user-hover&quot; rel=&quot;daniel.gottlieb&quot;&gt;daniel.gottlieb&lt;/a&gt; thank you for this clear and concise statement, it speaks the language I understand and helps me a lot in the reviews I&apos;m doing.&lt;/p&gt;</comment>
                            <comment id="2988897" author="daniel.gottlieb@10gen.com" created="Fri, 20 Mar 2020 13:38:52 +0000"  >&lt;p&gt;To make sure I got this right, I&apos;ll state my interpretation/understanding (which I&apos;m extending to include 4.0 so I understand the bigger picture):&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;MongoDB 4.0 runs in WT 3.1.0 and writes log version 3.&lt;/li&gt;
	&lt;li&gt;MongoDB 4.0 shutting down in FCV 3.6 will leave WT in a 3.0.0 state with log version 2&lt;/li&gt;
	&lt;li&gt;MongoDB 4.2.6+ will receive a backport that allows it to read log versions 4&lt;/li&gt;
	&lt;li&gt;In the absence of 4.2.6 explicitly calling &lt;tt&gt;wiredtiger_open&lt;/tt&gt; with &lt;tt&gt;compatibility=(release=3.2)&lt;/tt&gt;, it would write out data in 3.3.0/log version 4&lt;/li&gt;
	&lt;li&gt;MongoDB 4.4 will run in WT 10 and write log version 5&lt;/li&gt;
	&lt;li&gt;MongoDB 4.4 shutting down in FCV 4.2 will write out data in WT 3.3.0/log version 4&lt;/li&gt;
	&lt;li&gt;MongoDB 4.4 shutting down in FCV 4.4 will leave data in WT 10.0/log version 5&lt;/li&gt;
	&lt;li&gt;Compatibility version 3.3/log version 4 will only produced by MongoDB 4.4 that was shut down in FCV 4.2&lt;/li&gt;
	&lt;li&gt;For MongoDB 4.2.6, running with &lt;tt&gt;compatibility=(release=3.2)&lt;/tt&gt; will result in an unconfigured WT_CONNECTION::close to write out 3.2/log version 3 files. An explicit &lt;tt&gt;compatibility=(release=3.2)&lt;/tt&gt; is not needed to downgrade to 4.2.4-.&lt;/li&gt;
	&lt;li&gt;MongoDB 4.2.6 will also technically understand WT compatibility version 10.0/log version 5? (thus the requirement to &lt;tt&gt;require_max=3.3.0&lt;/tt&gt;)&lt;/li&gt;
&lt;/ul&gt;
</comment>
                            <comment id="2988696" author="alexander.gorrod" created="Fri, 20 Mar 2020 05:06:12 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=milkie&quot; class=&quot;user-hover&quot; rel=&quot;milkie&quot;&gt;milkie&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=daniel.gottlieb&quot; class=&quot;user-hover&quot; rel=&quot;daniel.gottlieb&quot;&gt;daniel.gottlieb&lt;/a&gt; would you mind taking a look at this? It&apos;s blocking some upgrade downgrade work, so I&apos;d appreciate it if we could get it addressed quickly.&lt;/p&gt;</comment>
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