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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-49171] [optimization] Optimize access to MigratingTenantAccessBlockers for better concurrency</title>
                <link>https://jira.mongodb.org/browse/SERVER-49171</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;&lt;b&gt;Original ticket name:&lt;/b&gt; Make Database have a shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt; decoration&lt;/p&gt;

&lt;p&gt;See &lt;a href=&quot;https://gist.github.com/EshaMaharishi/962ac67912d38a4a3a048fe757db43e8&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this gist&lt;/a&gt; for an explanation of the decorator pattern and how decorations are used in MongoDB.&lt;/p&gt;

&lt;p&gt;Make Database have a shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt; decoration. (The decoration should default to nullptr.) See&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/4eacc5768f3967882fe5edeeb7ec2739bb95a1a8/src/mongo/s/cluster_last_error_info.cpp#L39&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;example&lt;/a&gt; of a shared_ptr decoration on another object.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;EDIT:&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;Using a decoration on Database is difficult because there is no good way to synchronize access to it (besides using a database-level LockManager lock).&lt;/p&gt;

&lt;p&gt;Instead, let&apos;s create a MigratingTenantAccessBlockerByName class with standalone map from dbName -&amp;gt; shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt; that is protected by a member mutex, analogous to the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/e4f92ef12f233e86be9de019f16db4f5dde47ad5/src/mongo/db/s/collection_sharding_state.cpp#L104-L108&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;CollectionShardingStateMap&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;The class should be a decoration on ServiceContext (similarly to how &lt;a href=&quot;https://github.com/mongodb/mongo/blob/e4f92ef12f233e86be9de019f16db4f5dde47ad5/src/mongo/db/s/collection_sharding_state.cpp#L49&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;CollectionShardingStateMap is&lt;/a&gt;) and should go in migrating_tenant_access_blocker.cpp.&lt;/p&gt;

&lt;p&gt;The class should have the following methods:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;// Returns the MigratingTenantAccessBlocker for &apos;dbName&apos; if one exists, else returns nullptr.&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt; get(StringData dbName);&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&amp;nbsp;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;// Adds an entry for &apos;dbName&apos; with &apos;mtab&apos;.&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;void add(StringData dbName, shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt; mtab);&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&amp;nbsp;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;// Removes all entries for which &apos;dbPrefix&apos; is a prefix of the entry&apos;s &apos;dbName&apos;.&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;void removeAllWithPrefix(StringData dbPrefix);&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;
&lt;p&gt;and should have a private StringMap&amp;lt;std::shared_ptr&amp;lt;MigratingTenantAccessBlocker&amp;gt;&amp;gt;.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;EDIT 2:&lt;/b&gt;&lt;br/&gt;
 &#160;&lt;br/&gt;
 This ticket is more of an optimization, since we could have user reads/writes just check the byPrefix map. Getting an mtab by dbName from the byPrefix map will be slightly more expensive (if it&apos;s a tree map, the lookup will be O(log n) where n is the number of concurrent tenant migrations that have started blocking). But I don&apos;t expect there to ever be many concurrent tenant migrations, so that lookup should still be cheap.&lt;br/&gt;
 &#160;&lt;br/&gt;
 If we decide having an O(1) lookup is important or otherwise want to optimize for concurrency, we can revisit this ticket.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1394857">SERVER-49171</key>
            <summary>[optimization] Optimize access to MigratingTenantAccessBlockers for better concurrency</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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="esha.maharishi@mongodb.com">Esha Maharishi</reporter>
                        <labels>
                            <label>pm-1791_milestone-A</label>
                    </labels>
                <created>Mon, 29 Jun 2020 20:30:12 +0000</created>
                <updated>Tue, 6 Dec 2022 02:20:51 +0000</updated>
                            <resolved>Sat, 8 Aug 2020 03:35:11 +0000</resolved>
                                                                    <component>Replication</component>
                                        <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="3328946" author="esha.maharishi@10gen.com" created="Sat, 8 Aug 2020 03:35:11 +0000"  >&lt;p&gt;Closing this since rehosting the tenant migration donor&apos;s logic on Primary-Only Service means it will use the Primary-Only Service&apos;s catalog for managing tenant migration donor instances.&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10011">
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                                                                <inwardlinks description="is depended on by">
                                        <issuelink>
            <issuekey id="1395054">SERVER-49184</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="1395071">SERVER-49185</issuekey>
        </issuelink>
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