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    <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>[DOCS-14449] Investigate changes in SERVER-56307: The chunk migration &quot;convergence algorithm&quot; is very primitive</title>
                <link>https://jira.mongodb.org/browse/DOCS-14449</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;

    &lt;div class=&quot;panel&quot; style=&quot;background-color: #c2d2c2;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;background-color: #239eb0;&quot;&gt;&lt;b&gt;Downstream Change Summary&lt;/b&gt;&lt;/div&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #c2d2c2;&quot;&gt;
&lt;p&gt;    The changeset adds a new server parameter (&apos;minCatchUpPercentageBeforeBlockingWrites&apos;, loaded at startup time) to adjust the behaviour of the live migration protocol in the catchup phase.&lt;/p&gt;

&lt;p&gt;Higher percentage values anticipate the moment when incoming write operations over the data being migrated get suspended: this allows the migration protocol to converge earlier in situations of high load - at the cost of introducing an increased latency over concurrent upserts and deletes.&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h2&gt;&lt;a name=&quot;DescriptionofLinkedTicket&quot;&gt;&lt;/a&gt;Description of Linked Ticket&lt;/h2&gt;
&lt;p&gt;    The chunk migration &quot;convergence algorithm&quot; is the logic which the donor and participant implement in order for the donor to decide when to enter the critical section and block writes.&lt;/p&gt;

&lt;p&gt;The current implementation relies on the recipient being capable of&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/913217ab00e3597bf763e40904cdd159e7e8cb2b/src/mongo/db/s/migration_destination_manager.cpp#L1162&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;catching up on every modification occurred during the migration&lt;/a&gt;&#160;and reaching the STEADY state to allow the donor to enter the critical section.&lt;/p&gt;

&lt;p&gt;It has been detected that under situations of heavy load&#160;such condition may be never met, as the rate of incoming modifications is bigger than what can be transferred to the recipient.&lt;/p&gt;

&lt;p&gt;Potetial fixes are:&lt;/p&gt;

&lt;p&gt;(1) The donor sends to the recipient some measure of how much mods are left, so it can enter the steady state based on some delta, rather than zero.&lt;/p&gt;

&lt;p&gt;(2) The donor decides to enter the critical section not based on whether the recipient has decided to enter steady-state (which includes a&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/913217ab00e3597bf763e40904cdd159e7e8cb2b/src/mongo/db/s/migration_destination_manager.cpp#L1222&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;wait for majority&lt;/a&gt;)&lt;br/&gt;
(Option 2 might not be appropriate, though because it adds the recipient&apos;s majority wait under the critical section)&lt;/p&gt;


&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="1714379">DOCS-14449</key>
            <summary>Investigate changes in SERVER-56307: The chunk migration &quot;convergence algorithm&quot; is very primitive</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="jeffrey.allen@mongodb.com">Jeffrey Allen</assignee>
                                    <reporter username="backlog-server-pm">Backlog - Core Eng Program Management Team</reporter>
                        <labels>
                    </labels>
                <created>Thu, 13 May 2021 07:51:41 +0000</created>
                <updated>Mon, 13 Nov 2023 17:54:44 +0000</updated>
                            <resolved>Thu, 26 Aug 2021 16:17:18 +0000</resolved>
                                                    <fixVersion>4.2.15</fixVersion>
                    <fixVersion>4.4.7</fixVersion>
                    <fixVersion>4.0.26</fixVersion>
                    <fixVersion>5.0.0-rc3</fixVersion>
                    <fixVersion>5.1.0-rc0</fixVersion>
                    <fixVersion>Server_Docs_20231030</fixVersion>
                    <fixVersion>Server_Docs_20231106</fixVersion>
                    <fixVersion>Server_Docs_20231105</fixVersion>
                    <fixVersion>Server_Docs_20231113</fixVersion>
                                    <component>manual</component>
                    <component>Server</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="4024548" author="xgen-internal-githook" created="Thu, 26 Aug 2021 16:17:01 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jeff Allen&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-14449&quot; title=&quot;Investigate changes in SERVER-56307: The chunk migration &amp;quot;convergence algorithm&amp;quot; is very primitive&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-14449&quot;&gt;&lt;del&gt;DOCS-14449&lt;/del&gt;&lt;/a&gt;): maxCatchUpPercentageBeforeBlockingWrites server parameter&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/11015e548c96d1df3cc6c7bc58820014b7293060&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/11015e548c96d1df3cc6c7bc58820014b7293060&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4024523" author="xgen-internal-githook" created="Thu, 26 Aug 2021 16:10:29 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jeff Allen&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-14449&quot; title=&quot;Investigate changes in SERVER-56307: The chunk migration &amp;quot;convergence algorithm&amp;quot; is very primitive&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-14449&quot;&gt;&lt;del&gt;DOCS-14449&lt;/del&gt;&lt;/a&gt;): maxCatchUpPercentageBeforeBlockingWrites server parameter&lt;br/&gt;
Branch: v4.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/fa522b867c5dc7dd4c6380b443626ab67c4b8ec0&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/fa522b867c5dc7dd4c6380b443626ab67c4b8ec0&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4024505" author="xgen-internal-githook" created="Thu, 26 Aug 2021 16:02:32 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jeff Allen&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-14449&quot; title=&quot;Investigate changes in SERVER-56307: The chunk migration &amp;quot;convergence algorithm&amp;quot; is very primitive&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-14449&quot;&gt;&lt;del&gt;DOCS-14449&lt;/del&gt;&lt;/a&gt;): maxCatchUpPercentageBeforeBlockingWrites server parameter&lt;br/&gt;
Branch: v5.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/660765c3ef55873deaa3a5731fe4b80955cb1893&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/660765c3ef55873deaa3a5731fe4b80955cb1893&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4024495" author="xgen-internal-githook" created="Thu, 26 Aug 2021 16:00:39 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jeff Allen&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-14449&quot; title=&quot;Investigate changes in SERVER-56307: The chunk migration &amp;quot;convergence algorithm&amp;quot; is very primitive&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-14449&quot;&gt;&lt;del&gt;DOCS-14449&lt;/del&gt;&lt;/a&gt;): maxCatchUpPercentageBeforeBlockingWrites server parameter&lt;br/&gt;
Branch: v4.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/2a02f2d334d7ba2fe2456da06a1e34167c8e33f4&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/2a02f2d334d7ba2fe2456da06a1e34167c8e33f4&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4024481" author="xgen-internal-githook" created="Thu, 26 Aug 2021 15:57:16 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jeff Allen&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-14449&quot; title=&quot;Investigate changes in SERVER-56307: The chunk migration &amp;quot;convergence algorithm&amp;quot; is very primitive&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-14449&quot;&gt;&lt;del&gt;DOCS-14449&lt;/del&gt;&lt;/a&gt;): maxCatchUpPercentageBeforeBlockingWrites server parameter&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/6f202efc9993c8d40a135b0c407e5c0891faf922&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/6f202efc9993c8d40a135b0c407e5c0891faf922&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
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                                            <outwardlinks description="backported by">
                                        <issuelink>
            <issuekey id="1731273">DOCS-14468</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1742837">DOCS-14484</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1742886">DOCS-14485</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1792592">DOCS-14583</issuekey>
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            <issuekey id="1689612">SERVER-56307</issuekey>
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