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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-53274] The force-write of the `history` field to all chunks on FCV upgrade from 3.6 to 4.0 is unnecessary</title>
                <link>https://jira.mongodb.org/browse/SERVER-53274</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;With the (partial) introduction of the &lt;tt&gt;readAtCluster&lt;/tt&gt; time feature in version 4.0, we introduced the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/r4.0.20/src/mongo/s/catalog/type_chunk.h#L315&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;&lt;tt&gt;history&lt;/tt&gt;&lt;/a&gt; field to entries in &lt;tt&gt;config.chunks&lt;/tt&gt;. The FCV upgrade step from 3.6 to 4.0 forcefully &lt;a href=&quot;https://github.com/mongodb/mongo/blob/r4.0.20/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp#L954&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;writes the &lt;tt&gt;history&lt;/tt&gt;&lt;/a&gt; field to all chunks in the system and bumps their version in order for the cache to be able to see the change.&lt;/p&gt;

&lt;p&gt;This however, causes problems on upgrades, because it causes a total throw-out of the caches and also full rewrite of the local cache collections on the Shards, which in the case of many chunks can cause minutes of stall. These stalls on top of that are unpredictable and might not be related when the FCV command was run.&lt;/p&gt;

&lt;p&gt;I am fairly certain that we can throw out the force-write of the &lt;tt&gt;history&lt;/tt&gt; field and leave them to happen lazily. The code even in master is &lt;a href=&quot;https://github.com/mongodb/mongo/blob/51660945fb6662367f30e00b1a4685787ad9bd89/src/mongo/s/chunk.cpp#L54&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;prepared to handle&lt;/a&gt; the missing field.&lt;/p&gt;

&lt;p&gt;On downgrades I think it is also safe to not bother removing it. Older code will ignore it and if another upgrade is performed, there is no harm with having the values there, because they will map to a very old cluster time which will be smaller than the current one, so no harm.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1562465">SERVER-53274</key>
            <summary>The force-write of the `history` field to all chunks on FCV upgrade from 3.6 to 4.0 is unnecessary</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="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="jordi.serra-torrens@mongodb.com">Jordi Serra Torrens</assignee>
                                    <reporter username="kaloian.manassiev@mongodb.com">Kaloian Manassiev</reporter>
                        <labels>
                            <label>Sharding-EMEA</label>
                            <label>sharding-wfbf-day</label>
                    </labels>
                <created>Tue, 8 Dec 2020 13:43:08 +0000</created>
                <updated>Sun, 29 Oct 2023 21:59:41 +0000</updated>
                            <resolved>Fri, 5 Feb 2021 10:18:32 +0000</resolved>
                                    <version>4.0.21</version>
                                    <fixVersion>4.0.23</fixVersion>
                                    <component>Sharding</component>
                                        <votes>6</votes>
                                    <watches>10</watches>
                                                                                                                <comments>
                            <comment id="3765891" author="xgen-internal-githook" created="Tue, 11 May 2021 08:59:57 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jordi Serra Torrens&apos;, &apos;email&apos;: &apos;jordi.serra-torrens@mongodb.com&apos;, &apos;username&apos;: &apos;jordist&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-56795&quot; title=&quot;Changes from SERVER-53274 were unintentionally reverted&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-56795&quot;&gt;&lt;del&gt;SERVER-56795&lt;/del&gt;&lt;/a&gt; Changes from &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-53274&quot; title=&quot;The force-write of the `history` field to all chunks on FCV upgrade from 3.6 to 4.0 is unnecessary&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-53274&quot;&gt;&lt;del&gt;SERVER-53274&lt;/del&gt;&lt;/a&gt; were unintentionally reverted&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/70299e858e3f54c01fdb96cdd1c430972500b97f&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/70299e858e3f54c01fdb96cdd1c430972500b97f&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3601076" author="xgen-internal-githook" created="Fri, 5 Feb 2021 10:17:20 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jordi Serra Torrens&apos;, &apos;email&apos;: &apos;jordi.serra-torrens@mongodb.com&apos;, &apos;username&apos;: &apos;jordist&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-53274&quot; title=&quot;The force-write of the `history` field to all chunks on FCV upgrade from 3.6 to 4.0 is unnecessary&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-53274&quot;&gt;&lt;del&gt;SERVER-53274&lt;/del&gt;&lt;/a&gt; Avoid bumping all chunk versions after writing &apos;history&apos; field on FCV upgrade to 4.0.&lt;/p&gt;

&lt;p&gt;Instead, bump only one chunk per shard to satisfy the reqirements&lt;br/&gt;
imposed by &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-33356&quot; title=&quot;Ensure shards&amp;#39; persisted collection cache picks up collection UUIDs after setFCV=4.0&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-33356&quot;&gt;&lt;del&gt;SERVER-33356&lt;/del&gt;&lt;/a&gt;&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/52d6f11c459b8d3666379431a6accf7fef4e852f&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/52d6f11c459b8d3666379431a6accf7fef4e852f&lt;/a&gt;&lt;/p&gt;</comment>
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            <issuekey id="1708599">SERVER-56795</issuekey>
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