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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>
    </build-info>


<item>
            <title>[DOCS-12650] Manual restoration procedure for sharded clusters should mention disableLogicalSessionCacheRefresh</title>
                <link>https://jira.mongodb.org/browse/DOCS-12650</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;
&lt;p&gt;Starting with MongoDB v3.6 collections are assigned &lt;a href=&quot;https://docs.mongodb.com/manual/core/databases-and-collections/index.html#unique-identifiers&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;an immutable unique identifier (UUID)&lt;/a&gt;. The collection UUID remains the same across all members of a replica set and shards in a sharded cluster. That functionality comes into effect only after &lt;tt&gt;featureCompatibilityVersion&lt;/tt&gt; is set to v3.6. UUID is necessary for &lt;a href=&quot;https://docs.mongodb.com/manual/reference/server-sessions/index.html&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;Logical Sessions&lt;/a&gt; and transactions (introduced in v4.0).&lt;/p&gt;

&lt;p&gt;What it also means is that starting with v3.6 an oplog operation can fail if the UUID of the actual collection on the server does not match the UUID of the operation. That could be interpreted as inconsistency and therefore results into an abnormal termination of the `mongod` process (the crash you have experienced).&lt;/p&gt;

&lt;p&gt;It creates a problem with manual restoration of sharded clusters. Specifically, in &lt;a href=&quot;https://docs.mongodb.com/manual/tutorial/restore-sharded-cluster/#restore-the-shard-primary-mongod-data-files&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;step 1&lt;/a&gt; we say that the member of a shard needs to be started in standalone for certain manipulations with the metadata. The problem is that:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;If the user is restoring from an OM/CM snapshot&lt;/li&gt;
	&lt;li&gt;if it takes more than 5 minutes for to keep the member in standalone&lt;br/&gt;
Then the &lt;tt&gt;config.systems&lt;/tt&gt; collection will get created automatically on that member with UUID that will &lt;em&gt;NOT&lt;/em&gt; match the rest of the cluster. Later it can cause crashes (see HELP-6628) and possibly some other undefined behaviour.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;The solution is to make sure that when the node is started in standalone for the restore procedure, it is started with the &lt;tt&gt;disableLogicalSessionCacheRefresh&lt;/tt&gt; parameter (undocumented yet) enabled.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="744171">DOCS-12650</key>
            <summary>Manual restoration procedure for sharded clusters should mention disableLogicalSessionCacheRefresh</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="13201">Fixed</resolution>
                                        <assignee username="ravind.kumar">Ravind Kumar</assignee>
                                    <reporter username="dmitry.ryabtsev@mongodb.com">Dmitry Ryabtsev</reporter>
                        <labels>
                    </labels>
                <created>Wed, 24 Apr 2019 05:15:38 +0000</created>
                <updated>Mon, 30 Oct 2023 20:42:36 +0000</updated>
                            <resolved>Thu, 9 May 2019 15:52:20 +0000</resolved>
                                    <version>3.6.11</version>
                                    <fixVersion>Server_Docs_20231030</fixVersion>
                                    <component>Server</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="2240078" author="ravind.kumar" created="Thu, 9 May 2019 15:52:20 +0000"  >&lt;p&gt;pushed to 4.0-&amp;gt;3.6, published in turn.&lt;/p&gt;</comment>
                            <comment id="2240077" author="xgen-internal-githook" created="Thu, 9 May 2019 15:50:43 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;ravind.kumar@mongodb.com&apos;, &apos;name&apos;: &apos;rk-mongo&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12650&quot; title=&quot;Manual restoration procedure for sharded clusters should mention disableLogicalSessionCacheRefresh&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12650&quot;&gt;&lt;del&gt;DOCS-12650&lt;/del&gt;&lt;/a&gt;: OM/CM manual restore requires disableLogicalSessionCacheRefresh&lt;br/&gt;
Branch: v3.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/763f1abebff9bb2fd74308798c580e6987042362&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/763f1abebff9bb2fd74308798c580e6987042362&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2240067" author="xgen-internal-githook" created="Thu, 9 May 2019 15:49:20 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;ravind.kumar@mongodb.com&apos;, &apos;name&apos;: &apos;rk-mongo&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12650&quot; title=&quot;Manual restoration procedure for sharded clusters should mention disableLogicalSessionCacheRefresh&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12650&quot;&gt;&lt;del&gt;DOCS-12650&lt;/del&gt;&lt;/a&gt;: OM/CM manual restore requires disableLogicalSessionCacheRefresh&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/a4c0154dd3f62ac225941ae2af4125a54e52c124&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/a4c0154dd3f62ac225941ae2af4125a54e52c124&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2240062" author="xgen-internal-githook" created="Thu, 9 May 2019 15:46:20 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;rk-mongo&apos;, &apos;email&apos;: &apos;ravind.kumar@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12650&quot; title=&quot;Manual restoration procedure for sharded clusters should mention disableLogicalSessionCacheRefresh&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12650&quot;&gt;&lt;del&gt;DOCS-12650&lt;/del&gt;&lt;/a&gt;: OM/CM manual restore requires disableLogicalSessionCacheRefresh&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/27dcd9e8063d00400de801aba2ce48cce90aed78&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/27dcd9e8063d00400de801aba2ce48cce90aed78&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2226684" author="ravind.kumar" created="Fri, 26 Apr 2019 21:13:10 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-34683&quot; title=&quot;Downgrade replicaset from 3.6.4 to 3.4.14 fails due to the presence of `config.system.sessions`&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-34683&quot;&gt;&lt;del&gt;SERVER-34683&lt;/del&gt;&lt;/a&gt; indicates the flag should be available as of 3.6, so we&apos;re safe to backport once this is ready on &lt;tt&gt;master&lt;/tt&gt;&lt;/p&gt;</comment>
                            <comment id="2225473" author="dmitry.ryabtsev" created="Fri, 26 Apr 2019 00:13:00 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=ravind.kumar&quot; class=&quot;user-hover&quot; rel=&quot;ravind.kumar&quot;&gt;ravind.kumar&lt;/a&gt; I&apos;m not very concerned about the parameter being undocumented as long as the restoration procedure is updated for 3.6+.&lt;/p&gt;

&lt;blockquote&gt;&lt;p&gt;am I right in thinking this only applies for CM/OM snapshots since they drop config.system.sessions and config.transactions ?&lt;/p&gt;&lt;/blockquote&gt;

&lt;p&gt;Correct. Although there is a possibility that a user may try to restore a backup taken on 3.4 (that wouldn&apos;t have the sessions collection) with the v3.6 binaries,MongoDB would start in FCV 3.4 mode which,  to the best of my knowledge, will not run the sessions refresh thread and thus should be safe.&lt;/p&gt;

&lt;p&gt;So yeah, CM/OM snapshots restores only.&lt;/p&gt;</comment>
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