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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-13524] Why MongoDB starts to split before 64MB?</title>
                <link>https://jira.mongodb.org/browse/SERVER-13524</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I&apos;m testing the MongoDB Sharding with a Sharded Collection and a forloop to insert arround some documents to see how splitting and moving works.&lt;/p&gt;

&lt;p&gt;After 10K documents MongoDB has split my collection in 3 chunks, well before 64Mb (the default chunkSize):&lt;/p&gt;

&lt;p&gt;mongos&amp;gt; db.users.getShardDistribution()&lt;/p&gt;

&lt;p&gt;Shard rs0 at rs0/mongod00.local.net:2100,mongod01.local.net:2101&lt;br/&gt;
 data : 1.06MiB docs : 10000 chunks : 3&lt;br/&gt;
 estimated data per chunk : 364KiB&lt;br/&gt;
 estimated docs per chunk : 3333&lt;/p&gt;

&lt;p&gt;Totals&lt;br/&gt;
 data : 1.06MiB docs : 10000 chunks : 3&lt;br/&gt;
 Shard rs0 contains 100% data, 100% docs in cluster, avg obj size on shard : 112B&lt;/p&gt;

&lt;p&gt;It&apos;s not a problem but with this, I don&apos;t understant the interest of the chunkSize parameter.&lt;/p&gt;</description>
                <environment>MongoDB 2.4 and MongoDB 2.6</environment>
        <key id="130184">SERVER-13524</key>
            <summary>Why MongoDB starts to split before 64MB?</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="9">Done</resolution>
                                        <assignee username="ramon.fernandez@mongodb.com">Ramon Fernandez Marina</assignee>
                                    <reporter username="maxime.fouilleul@gmail.com">Maxime FOUILLEUL</reporter>
                        <labels>
                            <label>chunkSize</label>
                            <label>shard</label>
                            <label>split</label>
                    </labels>
                <created>Wed, 9 Apr 2014 15:50:30 +0000</created>
                <updated>Wed, 10 Dec 2014 23:11:37 +0000</updated>
                            <resolved>Tue, 29 Apr 2014 20:17:45 +0000</resolved>
                                                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="567311" author="ramon.fernandez" created="Tue, 29 Apr 2014 20:17:45 +0000"  >&lt;p&gt;Hi Maxime,&lt;/p&gt;

&lt;p&gt;I believe Randolph&apos;s reply answers your question so we&apos;re closing this issue. Feel free to re-open if you need further clarification.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
                            <comment id="542780" author="renctan" created="Wed, 9 Apr 2014 20:17:07 +0000"  >&lt;p&gt;Mongos tries to perform splits aggressively early on when there are only a few chunks in the sharded collection. The basic idea is to start distributing the chunks across the cluster early on while there isn&apos;t much data to move. If you are interested in the exact formula used, you can check it out here:&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/r2.6.0-rc3/src/mongo/s/chunk.cpp#L1427-1449&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/r2.6.0-rc3/src/mongo/s/chunk.cpp#L1427-1449&lt;/a&gt;&lt;/p&gt;</comment>
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