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    <title>MongoDB Jira</title>
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    <description>This file is an XML representation of an issue</description>
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        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-25652] Slow chunk migrations when there are large chunk counts. 3.0, 3.2, 3.3.11</title>
                <link>https://jira.mongodb.org/browse/SERVER-25652</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I&apos;ve been testing the speed of chunk migrations in an all-on-one-server test cluster. Even when the chunks being migrated are empty (i.e. the chunk move takes only ~0.1 secs) the entire cycle run by the balancer takes a lot longer. &lt;/p&gt;

&lt;div class=&apos;table-wrap&apos;&gt;
&lt;table class=&apos;confluenceTable&apos;&gt;&lt;tbody&gt;
&lt;tr&gt;
&lt;th class=&apos;confluenceTh&apos;&gt; version &lt;/th&gt;
&lt;th class=&apos;confluenceTh&apos;&gt; balance round time &lt;/th&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; 3.0.8 &lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; ~4.5 secs &lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; v3.3.11-30-gc96009e &lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; ~ 9 secs &lt;/td&gt;
&lt;/tr&gt;
&lt;/tbody&gt;&lt;/table&gt;
&lt;/div&gt;


&lt;p&gt;From someone&apos;s else case with v3.2 and different servers / network to my test I heard of a ~6 second cycle. Not sure if that was a replica set config db or the older SCCC-style one.&lt;/p&gt;

&lt;p&gt;Can the balancer be changed so that the balance round will do multiple chunks of each collection so long as they finish quickly? E.g. balance round identifies candidate chunks for migrations, and keeps on doing chunk moves for them serially until a, say, 10 sec window completes.&lt;/p&gt;

&lt;p&gt;At any rate if data has been completely deleted for a big fraction of chunk ranges before adding a new shard, it would be good if those chunks moves happened a lot more quickly.&lt;/p&gt;</description>
                <environment></environment>
        <key id="309529">SERVER-25652</key>
            <summary>Slow chunk migrations when there are large chunk counts. 3.0, 3.2, 3.3.11</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="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="kaloian.manassiev@mongodb.com">Kaloian Manassiev</assignee>
                                    <reporter username="akira.kurogane">Akira Kurogane</reporter>
                        <labels>
                    </labels>
                <created>Wed, 17 Aug 2016 01:49:59 +0000</created>
                <updated>Mon, 31 Oct 2016 15:13:09 +0000</updated>
                            <resolved>Thu, 27 Oct 2016 19:10:55 +0000</resolved>
                                    <version>3.0.8</version>
                    <version>3.3.11</version>
                                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="1419809" author="kaloian.manassiev" created="Thu, 27 Oct 2016 19:10:42 +0000"  >&lt;p&gt;There are multiple aspects of the chunk migration process which contribute to the speed of migration in the case where there are no documents in the chunks and these have been isolated in the related tickets. This ticket will be closed in lieu of these more specific tickets.&lt;/p&gt;</comment>
                            <comment id="1362058" author="dianna.hohensee" created="Fri, 19 Aug 2016 14:24:35 +0000"  >&lt;p&gt;Okay, no problem. I&apos;m not sure exactly when we&apos;ll start testing, so if you get a chance, great, if we get there first, that&apos;s fine too.&lt;/p&gt;

&lt;p&gt;Thanks again for the JS you did attach.&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
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                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="326773">SERVER-26770</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="327065">SERVER-26791</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="326835">SERVER-26778</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="324774">SERVER-26684</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="326818">SERVER-26777</issuekey>
        </issuelink>
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                            <attachment id="135571" name="chunksOnWrongTier_v2.js" size="1455" author="dianna.hohensee@mongodb.com" created="Thu, 18 Aug 2016 19:30:18 +0000"/>
                            <attachment id="135572" name="createChunks_v3.js" size="2634" author="dianna.hohensee@mongodb.com" created="Thu, 18 Aug 2016 19:30:18 +0000"/>
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	&lt;li&gt;Create two-shard cluster;&lt;/li&gt;
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&lt;em&gt;(100k chunks may be enough to make noticeable differences, but it has been at 500k that it becomes very easy to observe.)&lt;/em&gt;&lt;/li&gt;
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