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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-68777] BalancerCollectionStatus may report balancerCompliant too early</title>
                <link>https://jira.mongodb.org/browse/SERVER-68777</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-67301&quot; title=&quot;Balancer may perform one unnecessary migration for a completely balanced collection&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-67301&quot;&gt;&lt;del&gt;SERVER-67301&lt;/del&gt;&lt;/a&gt; tried to fix the problem that the balancer may make wrong decisions based on the amount of data because of the non transactionality of deleting orphans and updating the orphan counter. However, there is another problem related to this.&lt;/p&gt;

&lt;p&gt;Suppose we have 8.1MB of documents and 1MB orphans (total of 9.1MB) on one shard and 5MB of documents on a second shard (with a max chunk size of 1MB)&lt;/p&gt;

&lt;p&gt;If the orphans are deleted but the orphan counter is not updated when the balancer asks for datasize, the first shard will report 8.1MB of data minus 1MB orphans (7.1MB) and the second shard will report 5MB data. The balancer will return balancerCompliant since the difference in data is 2.1MB which is less than 3 * 1MB.&lt;/p&gt;

&lt;p&gt;Then the orphan counter will be updated and the next round, the first shard will report 8.1MB of data (no orphans) and the second shard will report 5MB of data. The difference is 3.1MB of data and so a chunk will need to be moved from the first shard to the second shard.&lt;/p&gt;

&lt;p&gt;On the resolution of this ticket, take into account to remove the &lt;a href=&quot;https://github.com/10gen/mongo/blob/d5259b97c1beec7a996898f32c51046d1a497f8a/src/mongo/shell/utils_sh.js#L346-L355&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;extra check&lt;/a&gt; of the collection balance status on testing function &lt;a href=&quot;https://github.com/10gen/mongo/blob/d5259b97c1beec7a996898f32c51046d1a497f8a/src/mongo/shell/utils_sh.js#L320&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;awaitCollectionBalance&lt;/a&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2112238">SERVER-68777</key>
            <summary>BalancerCollectionStatus may report balancerCompliant too early</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="2">Won&apos;t Fix</resolution>
                                        <assignee username="silvia.surroca@mongodb.com">Silvia Surroca</assignee>
                                    <reporter username="allison.easton@mongodb.com">Allison Easton</reporter>
                        <labels>
                            <label>sharding-wfbf-day</label>
                    </labels>
                <created>Fri, 12 Aug 2022 07:54:38 +0000</created>
                <updated>Thu, 29 Sep 2022 09:44:42 +0000</updated>
                            <resolved>Thu, 29 Sep 2022 09:44:42 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="4864486" author="JIRAUSER1268536" created="Thu, 29 Sep 2022 09:44:42 +0000"  >&lt;p&gt;We&apos;ve decided to don&apos;t fix this issue since the solution would slow down the balancer.&lt;br/&gt;
In more detail, the proper solution would execute atomically the &lt;a href=&quot;https://github.com/10gen/mongo/blob/31120c1c588d0f7b998842ea529fa613d3a45486/src/mongo/db/s/range_deletion_util.cpp#L356-L360&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;remove of a range deletion&lt;/a&gt; and the &lt;a href=&quot;https://github.com/10gen/mongo/blob/31120c1c588d0f7b998842ea529fa613d3a45486/src/mongo/db/s/range_deletion_util.cpp#L372&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;update of the orphan counter&lt;/a&gt; from the balancer point of view, so that the balancer performance would be adversely affected.&lt;/p&gt;</comment>
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            <issuekey id="2069160">SERVER-67301</issuekey>
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            <issuekey id="2122137">SERVER-69136</issuekey>
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