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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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            <title>[SERVER-45703] Make CollectionShardingStateMap copy-on-write/otherwise lock-free</title>
                <link>https://jira.mongodb.org/browse/SERVER-45703</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The CollectionShardingState must be accessed on nearly every operation in a sharded cluster, which leads to a lot of contention on &lt;a href=&quot;https://github.com/mongodb/mongo/blob/5c6980b08a288fbd178c918ecae5efca8717ff3c/src/mongo/db/s/collection_sharding_state.cpp#L100&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this mutex&lt;/a&gt;, as seen in a local perf run (though of course that&apos;s not a perfect representation). Because currently we never delete items from the map (it&apos;s append-only), and we only rarely add new items (on sharded collection creation), I think it would be a good candidate for a lock-free copy-on-write data structure, which would allow reads which do not create new entries to occur with only a few atomic reads rather than a full mutex acquisition. It would be pretty easy to try this and perf test it. At the very least, we could change the mutex to a ResourceMutex so that reads only require a SharedLock rather than an exclusive lock. &lt;/p&gt;</description>
                <environment></environment>
        <key id="1109571">SERVER-45703</key>
            <summary>Make CollectionShardingStateMap copy-on-write/otherwise lock-free</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="12300">Won&apos;t Do</resolution>
                                        <assignee username="backlog-server-sharding">[DO NOT USE] Backlog - Sharding Team</assignee>
                                    <reporter username="matthew.saltz@mongodb.com">Matthew Saltz</reporter>
                        <labels>
                    </labels>
                <created>Wed, 22 Jan 2020 17:08:29 +0000</created>
                <updated>Tue, 6 Dec 2022 02:37:43 +0000</updated>
                            <resolved>Fri, 14 Feb 2020 16:13:46 +0000</resolved>
                                                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="2878581" author="esha.maharishi@10gen.com" created="Fri, 14 Feb 2020 16:13:46 +0000"  >&lt;p&gt;Closing the ticket but linked on the sharding pain points doc to track the context in this ticket.&lt;/p&gt;</comment>
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