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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-51108] Performance impact when enabling FCV 4.0</title>
                <link>https://jira.mongodb.org/browse/SERVER-51108</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Hello,&lt;/p&gt;

&lt;p&gt;We have a quite large cluster (over 20 shards / multiple databases and collections / config database having over 1M documents in chunk collection) . We&apos;ve observed impact during setting FCV to 4.0 on such a cluster while the whole cluster &quot;freezes&quot; when cache chunks are refreshed on each shard.&lt;/p&gt;

&lt;p&gt;============&lt;/p&gt;

&lt;p&gt;My understanding of the setting of FCV in case of 4.0 is:&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;FCV is triggered on mongos :&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/91e3352a1aa717674575fce3cc6edb2f279a4479/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/91e3352a1aa717674575fce3cc6edb2f279a4479/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;mongos sends the command to config servers:&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/91e3352a1aa717674575fce3cc6edb2f279a4479/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp#L94&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/91e3352a1aa717674575fce3cc6edb2f279a4479/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp#L94&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;config replicaset executes&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;it does that through the block dedicated to config server:&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp#L184&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp#L184&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;Within this block config will update to new FCV and trigger upgradeChunksHistory for each collection.&lt;/li&gt;
	&lt;li&gt;It will trigger the upgrade of FCV on each shard:&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp#L226&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/v4.0/src/mongo/db/commands/set_feature_compatibility_version_command.cpp#L226&lt;/a&gt;.&lt;/li&gt;
	&lt;li&gt;setting FCV on config replicaset.&lt;br/&gt;
===============================&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;Upgrade was performed from 3.6.10 to 4.0.15.&lt;/p&gt;

&lt;p&gt;Is there any way to mitigate the impact of enabling FCV on large cluster with lots of chunks?&lt;/p&gt;

&lt;p&gt;Thank you,&lt;/p&gt;

&lt;p&gt;Cristian&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="1485111">SERVER-51108</key>
            <summary>Performance impact when enabling FCV 4.0</summary>
                <type id="6" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Question</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="3">Duplicate</resolution>
                                        <assignee username="dmitry.agranat@mongodb.com">Dmitry Agranat</assignee>
                                    <reporter username="radan@adobe.com">Cristian Radan</reporter>
                        <labels>
                    </labels>
                <created>Wed, 23 Sep 2020 16:19:22 +0000</created>
                <updated>Tue, 3 Nov 2020 15:57:40 +0000</updated>
                            <resolved>Wed, 30 Sep 2020 13:20:47 +0000</resolved>
                                    <version>4.0.15</version>
                                                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="3418402" author="dmitry.agranat" created="Wed, 30 Sep 2020 13:20:20 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=radan%40adobe.com&quot; class=&quot;user-hover&quot; rel=&quot;radan@adobe.com&quot;&gt;radan@adobe.com&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;Among other improvements, the most relevant ticket for the reported issue is &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-49544&quot; title=&quot;Config server should send setFCV to all shards in parallel&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-49544&quot;&gt;SERVER-49544&lt;/a&gt;. I will link your report to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-49544&quot; title=&quot;Config server should send setFCV to all shards in parallel&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-49544&quot;&gt;SERVER-49544&lt;/a&gt; and resolve as a duplicate. You can watch &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-49544&quot; title=&quot;Config server should send setFCV to all shards in parallel&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-49544&quot;&gt;SERVER-49544&lt;/a&gt; for updates.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Dima&lt;/p&gt;</comment>
                            <comment id="3409025" author="dmitry.agranat" created="Thu, 24 Sep 2020 09:12:27 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=radan%40adobe.com&quot; class=&quot;user-hover&quot; rel=&quot;radan@adobe.com&quot;&gt;radan@adobe.com&lt;/a&gt;, thank you for the report.&lt;/p&gt;

&lt;p&gt;We do have some improvements in this area but these are aimed at 4.4. I am checking if any of these improvements are aimed to be backported to earlier versions.&lt;/p&gt;

&lt;p&gt;Thanks,&lt;br/&gt;
Dima&lt;/p&gt;</comment>
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