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        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-21245] Understanding query routing in tag-aware sharding setup</title>
                <link>https://jira.mongodb.org/browse/SERVER-21245</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Setup:&lt;br/&gt;
We have a sharding setup with tag-aware sharding and 22 shards. Each shard is a replica set consisting of 2 hosts and a backup replica (3 nodes in repset config)&lt;/p&gt;

&lt;p&gt;Issue:&lt;br/&gt;
We are facing issues where our mongod process is hitting 100% CPU usage on 1 thread and everything slows down.&lt;/p&gt;

&lt;p&gt;Details:&lt;br/&gt;
We use tag-aware sharding to spread collections between shards.&lt;br/&gt;
Thus we have shards which only have data for specific database/collections.&lt;br/&gt;
We wonder, why we see querys (removes and updates) on shards which have no data for this database/collection. (All found in slow query log)&lt;br/&gt;
Due to this remove extra querys on 1 of our shards the lock &quot;scheduler&quot; went crazy and CPU usage where at 100% (1 thread) while IOPS and mongod operations got stalled.&lt;/p&gt;

&lt;p&gt;1) Is it by design that remove commands are sent to all shards in a cluster even databse/collections doesn&apos;t exists on all shards?&lt;br/&gt;
2) Why do we see update querys on shards which don&apos;t have this database/collection?&lt;/p&gt;</description>
                <environment></environment>
        <key id="237249">SERVER-21245</key>
            <summary>Understanding query routing in tag-aware sharding setup</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="9">Done</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="steffen">Steffen</reporter>
                        <labels>
                    </labels>
                <created>Mon, 2 Nov 2015 13:31:52 +0000</created>
                <updated>Mon, 2 Nov 2015 15:14:30 +0000</updated>
                            <resolved>Mon, 2 Nov 2015 14:26:30 +0000</resolved>
                                    <version>3.0.4</version>
                                                                        <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="1076750" author="steffen" created="Mon, 2 Nov 2015 15:14:30 +0000"  >&lt;p&gt;To determine if it&apos;s a bug or not we need to know if it works as designed.&lt;/p&gt;</comment>
                            <comment id="1076692" author="ramon.fernandez" created="Mon, 2 Nov 2015 14:26:15 +0000"  >&lt;p&gt;Steffen, please note that the SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the &lt;a href=&quot;http://groups.google.com/group/mongodb-user&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;mongodb-user group&lt;/a&gt; or &lt;a href=&quot;http://stackoverflow.com/questions/tagged/mongodb&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;Stack Overflow with the &lt;tt&gt;mongodb&lt;/tt&gt; tag&lt;/a&gt;, where your question will reach a larger audience. A question like this involving more discussion would be best posted on the &lt;a href=&quot;http://groups.google.com/group/mongodb-user&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;mongodb-user group&lt;/a&gt;. See also our &lt;a href=&quot;https://www.mongodb.org/about/support/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;Technical Support page&lt;/a&gt; for additional support resources.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
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