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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <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-5066] mongos splits should back off when metadata lock is taken and splitting $max or $min</title>
                <link>https://jira.mongodb.org/browse/SERVER-5066</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;If a large migration is occurring in a collection with high insert rate, it&apos;s likely that repeated splitVector commands will be triggered by these inserts.  Because the collection metadata distributed lock is taken, the split will (correctly) fail, but not before the splitVector command is run on the mongod and the config server is checked.  If the chunk to be split is the $max or $min chunk, the amount of inserted data to the chunk is not changed, and every subsequent update and insert to these chunks will trigger a splitVector and splitChunk command.&lt;/p&gt;

&lt;p&gt;One optimization for all splits would be to have the mongos itself check the distributed lock, to avoid the splitVector if the split will just fail.  For $max/$min inserts, we need to either reset _dataWritten or back off in some other way.&lt;/p&gt;

&lt;p&gt;Can be seen occurring in &lt;a href=&quot;http://buildbot.mongodb.org/builders/Linux%2064-bit%20v8/builds/3032/steps/test_3/logs/stdio/text&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://buildbot.mongodb.org/builders/Linux%2064-bit%20v8/builds/3032/steps/test_3/logs/stdio/text&lt;/a&gt;&lt;br/&gt;
when the migration in bigMapReduce.js starting here :&lt;/p&gt;

&lt;p/&gt;
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&lt;p/&gt;

&lt;p&gt;results in ~150 splitVector requests from a single mongos.&lt;/p&gt;</description>
                <environment></environment>
        <key id="31469">SERVER-5066</key>
            <summary>mongos splits should back off when metadata lock is taken and splitting $max or $min</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="randolph@mongodb.com">Randolph Tan</assignee>
                                    <reporter username="greg_10gen">Greg Studer</reporter>
                        <labels>
                    </labels>
                <created>Fri, 24 Feb 2012 15:40:18 +0000</created>
                <updated>Wed, 10 Dec 2014 23:05:53 +0000</updated>
                            <resolved>Thu, 25 Sep 2014 17:36:27 +0000</resolved>
                                                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>6</watches>
                                                                                                                <comments>
                            <comment id="727207" author="renctan" created="Thu, 25 Sep 2014 17:27:08 +0000"  >&lt;p&gt;This is no longer true in master due to the changes in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13402&quot; title=&quot;bulk insert can result in too large chunks&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13402&quot;&gt;&lt;del&gt;SERVER-13402&lt;/del&gt;&lt;/a&gt;. The _dataWritten variable is now always cleared when the thread fails to get the distributed locks.&lt;/p&gt;</comment>
                            <comment id="200256" author="badgeville" created="Tue, 27 Nov 2012 16:28:55 +0000"  >&lt;p&gt;We ran into a similar issue.  There was a collection whose shard ID wasn&apos;t unique as it was supposed to be, because we were hashing the key on &apos;nil&apos;,  so the chunk got to 4G and all of the mongos agents tried to split it at the same time, killing performance.  Bug was ours, in that the document didn&apos;t have the correct shard key,  but just mentioning it in case you may have a similar issue.. May be something having to do with 4G.. 32 bits.. &lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;wedge&lt;/li&gt;
&lt;/ul&gt;
</comment>
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