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    <title>MongoDB Jira</title>
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    <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-66002] Optimize `maxChunkSize` discovery/retrieval on config server</title>
                <link>https://jira.mongodb.org/browse/SERVER-66002</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Following the introduction of the optional &lt;a href=&quot;https://github.com/mongodb/mongo/blob/53ce56437ce9df0bcb3c588b37ab86e484db2f99/src/mongo/s/catalog/type_collection.idl#L104-L107&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;per-collection maxChunkSize&lt;/a&gt; in v5.1, when issuing moves the balancer has first to check whether a collection has a configured value or - if not - rely on the &lt;a href=&quot;https://www.mongodb.com/docs/manual/tutorial/modify-chunk-size-in-sharded-cluster/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;global value&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;This has led to a lot of inefficiency in discovering the max chunk size for a given collection since the catalog entry is continuously retrieved from disk when needing to balance (this happens for example when calling &lt;a href=&quot;https://github.com/mongodb/mongo/blob/53ce56437ce9df0bcb3c588b37ab86e484db2f99/src/mongo/db/s/balancer/balancer.cpp#L204-L212&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;those functions&lt;/a&gt;).&lt;/p&gt;

&lt;p&gt;Moreover, with the modifications being done for the &quot;no more auto splitter&quot; project, the max chunk size is gaining more importance and needs to be retrieved/used in more parts in the code.&lt;/p&gt;

&lt;p&gt;Purpose of this ticket is to:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Allow to retrieve per-collection maxChunkSize from the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/53ce56437ce9df0bcb3c588b37ab86e484db2f99/src/mongo/s/balancer_configuration.cpp#L91&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;balancer configuration&lt;/a&gt; rather than populating the code with plenty of calls to the catalog client. This can be as simple of offering a method that is retrieving the value from the catalog without the caller having to manually do it.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;A further optimization - that can be offloaded in a follow-up ticket if too complex - would be to make the balancer configuration keep track in-memory of per-collection and global chunk sizes, with those value being updated via observers when their state changes on disk.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="2034133">SERVER-66002</key>
            <summary>Optimize `maxChunkSize` discovery/retrieval on config server</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="12300">Won&apos;t Do</resolution>
                                        <assignee username="allison.easton@mongodb.com">Allison Easton</assignee>
                                    <reporter username="pierlauro.sciarelli@mongodb.com">Pierlauro Sciarelli</reporter>
                        <labels>
                    </labels>
                <created>Wed, 27 Apr 2022 08:01:46 +0000</created>
                <updated>Thu, 28 Apr 2022 06:53:57 +0000</updated>
                            <resolved>Thu, 28 Apr 2022 06:53:56 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="4512055" author="allison.easton" created="Thu, 28 Apr 2022 06:53:57 +0000"  >&lt;p&gt;Since max chunk size is refreshed only at the beginning of the balancer round anyways and therefore is a best effort parameter, we will just continue to use the value from the balancer config refresh.&lt;/p&gt;</comment>
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