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    <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-77606] Reads concurrent with create index that also modifies multikey errors fail to find collection</title>
                <link>https://jira.mongodb.org/browse/SERVER-77606</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Reading concurrently with a create index DDL operation that also modifies multikey fails. There is a&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/6fbfe305e9c6e25f3764c63a5bfe970fa1d78214/src/mongo/db/catalog/collection_catalog.cpp#L994-L1010&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;condition&lt;/a&gt;&#160;inside&#160;&lt;tt&gt;establishConsistentCollection&lt;/tt&gt;&#160;when, in addition to the DDL operation, a multikey setting has also changed.&lt;/p&gt;

&lt;p&gt;When instantiating the collection for the read, we look for the shared index ident in both the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/4954cb44e1ceeda02db1902ffd7ea89d08c7b04c/src/mongo/db/catalog/collection_impl.cpp#L219-L250&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;provided IndexCatalog and inside the drop pending reaper.&lt;/a&gt; If it isn&apos;t found in either we will simply&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/4954cb44e1ceeda02db1902ffd7ea89d08c7b04c/src/mongo/db/catalog/collection_impl.cpp#L441&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;fail&lt;/a&gt;&#160;to&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/4954cb44e1ceeda02db1902ffd7ea89d08c7b04c/src/mongo/db/catalog/collection_catalog.cpp#L1169-L1171&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;create the collection&lt;/a&gt;, and lookups by UUID/Namespace will return&#160;&lt;tt&gt;nullptr&lt;/tt&gt;&#160;for the remainder of this operation.&lt;/p&gt;

&lt;p&gt;When an index is added it will only be in the index catalog for the collection instance in the pending commit state, but &lt;tt&gt;latestCollection&lt;/tt&gt; is passed to the caller &lt;a href=&quot;https://github.com/mongodb/mongo/blob/4954cb44e1ceeda02db1902ffd7ea89d08c7b04c/src/mongo/db/catalog/collection_catalog.cpp#L1002&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;. Causing the instantiation to fail and the read believes that the collection doesn&apos;t exist.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2354161">SERVER-77606</key>
            <summary>Reads concurrent with create index that also modifies multikey errors fail to find collection</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="henrik.edin@mongodb.com">Henrik Edin</assignee>
                                    <reporter username="henrik.edin@mongodb.com">Henrik Edin</reporter>
                        <labels>
                    </labels>
                <created>Tue, 30 May 2023 20:41:21 +0000</created>
                <updated>Sun, 29 Oct 2023 21:20:43 +0000</updated>
                            <resolved>Wed, 31 May 2023 16:29:49 +0000</resolved>
                                                    <fixVersion>7.1.0-rc0</fixVersion>
                    <fixVersion>7.0.0-rc3</fixVersion>
                                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="5464866" author="xgen-internal-githook" created="Wed, 31 May 2023 17:29:49 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;henrikedin&apos;, &apos;email&apos;: &apos;henrik.edin@mongodb.com&apos;, &apos;username&apos;: &apos;henrikedin&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-77606&quot; title=&quot;Reads concurrent with create index that also modifies multikey errors fail to find collection&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-77606&quot;&gt;&lt;del&gt;SERVER-77606&lt;/del&gt;&lt;/a&gt; Fix issue where reads fail to find collection.&lt;/p&gt;

&lt;p&gt;Reading concurrently with a DDL operation adding an index to the index catalog and also doing some multikey changes can fail to find the collection.&lt;/p&gt;

&lt;p&gt;We reach a fallback in establishConsistentCollection where the metadata of either instance doesn&apos;t match the snapshot. When instantiating the collection for the read we need to use the collection in pending commit as the base as it might contain an index visible in the storage engine snapshot.&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 6b4665df960009b21bec4c47ffcb50e155e610f0)&lt;br/&gt;
Branch: v7.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/58c26d5a0c76a96de54c3e8b97fd0ee89b1c720b&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/58c26d5a0c76a96de54c3e8b97fd0ee89b1c720b&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5464433" author="xgen-internal-githook" created="Wed, 31 May 2023 15:48:17 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;henrikedin&apos;, &apos;email&apos;: &apos;henrik.edin@mongodb.com&apos;, &apos;username&apos;: &apos;henrikedin&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-77606&quot; title=&quot;Reads concurrent with create index that also modifies multikey errors fail to find collection&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-77606&quot;&gt;&lt;del&gt;SERVER-77606&lt;/del&gt;&lt;/a&gt; Fix issue where reads fail to find collection.&lt;/p&gt;

&lt;p&gt;Reading concurrently with a DDL operation adding an index to the index catalog and also doing some multikey changes can fail to find the collection.&lt;/p&gt;

&lt;p&gt;We reach a fallback in establishConsistentCollection where the metadata of either instance doesn&apos;t match the snapshot. When instantiating the collection for the read we need to use the collection in pending commit as the base as it might contain an index visible in the storage engine snapshot.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/6b4665df960009b21bec4c47ffcb50e155e610f0&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/6b4665df960009b21bec4c47ffcb50e155e610f0&lt;/a&gt;&lt;/p&gt;</comment>
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