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<item>
            <title>[SERVER-78268] Remove shard slows down when there are multiple sharded collections and jumbo chunks</title>
                <link>https://jira.mongodb.org/browse/SERVER-78268</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;&lt;font color=&quot;#172b4d&quot;&gt;&lt;b&gt;Context&lt;/b&gt;&lt;/font&gt;&lt;/p&gt;

&lt;p&gt;When the balancer is selecting the chunks to move, it goes through all the collections randomly.&lt;/p&gt;

&lt;p&gt;To prioritize the migrations from the draining shards, for every collection, we first check if the collection has chunks on a draining shard.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;What is wrong&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;If a draining shard exists and that collection has chunks that can&apos;t be migrated from the draining shard (like jumbo chunks), &lt;a href=&quot;https://github.com/10gen/mongo/blob/47479f770419b9bbd0ed5045d63851f189dde7ee/src/mongo/db/s/balancer/balancer_policy.cpp#L412&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;that shard will be removed from the list of available shards to participate in&#160; a migration during the current balancing round&lt;/a&gt;, which is not correct. That removal means that, during the current balancing round, the next collections won&apos;t have any chance to move their chunks from that shard.&lt;/p&gt;

&lt;p&gt;Therefore, the draining of a shard has been slowed down due to the addition of &lt;a href=&quot;https://github.com/10gen/mongo/blob/47479f770419b9bbd0ed5045d63851f189dde7ee/src/mongo/db/s/balancer/balancer_policy.cpp#L412&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this&lt;/a&gt; line.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2373474">SERVER-78268</key>
            <summary>Remove shard slows down when there are multiple sharded collections and jumbo chunks</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-server-catalog-and-routing">Backlog - Catalog and Routing</assignee>
                                    <reporter username="silvia.surroca@mongodb.com">Silvia Surroca</reporter>
                        <labels>
                            <label>oldshardingemea</label>
                            <label>shardingemea-qw</label>
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                <created>Wed, 21 Jun 2023 11:04:46 +0000</created>
                <updated>Thu, 26 Oct 2023 10:09:46 +0000</updated>
                                                                                                <votes>0</votes>
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