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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-44771] Allow operations in transactions to safely consult the CatalogCache on mongod</title>
                <link>https://jira.mongodb.org/browse/SERVER-44771</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;When brainstorming the design for &lt;tt&gt;$unionWith&lt;/tt&gt;, we are concerned about an issue we have previously run into in such a scenario. &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=esha.maharishi&quot; class=&quot;user-hover&quot; rel=&quot;esha.maharishi&quot;&gt;esha.maharishi&lt;/a&gt; sums up a possible deadlock that can occur when a shard tries to look at the CatalogCache while still holding a lock in &lt;a href=&quot;https://jira.mongodb.org/browse/BF-10722?focusedCommentId=2031771&amp;amp;page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-2031771&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;this comment&lt;/a&gt;. It&apos;s also described in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-37398&quot; title=&quot;Concurrent aggregations with $out on a shard server can deadlock with each other&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-37398&quot;&gt;&lt;del&gt;SERVER-37398&lt;/del&gt;&lt;/a&gt; where we added &lt;a href=&quot;https://github.com/mongodb/mongo/blob/762e983eb72fa048ba00ab46c384458d308a461c/src/mongo/s/catalog_cache.cpp#L124-L127&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this invariant&lt;/a&gt; to ensure this never happens. This was discovered when working with improved $out (now branded as $merge), but it has implications for sharded $lookup and now $unionWith. &lt;/p&gt;

&lt;p&gt;This ticket tracks a feature request to remove that invariant. It should be possible to query a different shard using the CatalogCache while you are in a transaction (and thus hold some locks which you cannot drop). Currently you cannot do this because it may deadlock.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1018532">SERVER-44771</key>
            <summary>Allow operations in transactions to safely consult the CatalogCache on mongod</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="tommaso.tocci@mongodb.com">Tommaso Tocci</assignee>
                                    <reporter username="charlie.swanson@mongodb.com">Charlie Swanson</reporter>
                        <labels>
                    </labels>
                <created>Thu, 21 Nov 2019 17:08:50 +0000</created>
                <updated>Sun, 29 Oct 2023 22:14:43 +0000</updated>
                            <resolved>Fri, 14 Feb 2020 12:23:17 +0000</resolved>
                                                    <fixVersion>4.3.4</fixVersion>
                                    <component>Aggregation Framework</component>
                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="2878233" author="xgen-internal-githook" created="Fri, 14 Feb 2020 12:12:36 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;toto-dev&apos;, &apos;name&apos;: &apos;Tommaso Tocci&apos;, &apos;email&apos;: &apos;tommaso.tocci@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44771&quot; title=&quot;Allow operations in transactions to safely consult the CatalogCache on mongod&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44771&quot;&gt;&lt;del&gt;SERVER-44771&lt;/del&gt;&lt;/a&gt; Introduce 2nd CatalogCache for filtering only&lt;/p&gt;

&lt;p&gt;Only on ShardServer (not ReadOnly) use a second catalog cache for&lt;br/&gt;
filtering only in order to allow operations in transactions to safely&lt;br/&gt;
consult the CatalogCache.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/c25f0bc16a1f515f20972f30abf6bd569235a00f&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/c25f0bc16a1f515f20972f30abf6bd569235a00f&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2876705" author="tommaso.tocci" created="Thu, 13 Feb 2020 16:15:29 +0000"  >&lt;p&gt;Blocked by  &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-46131&quot; title=&quot;Fix race in retry loops in MigrationSourceManager&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-46131&quot;&gt;&lt;del&gt;SERVER-46131&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2845146" author="xgen-internal-githook" created="Sat, 8 Feb 2020 01:29:53 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;will62794&apos;, &apos;name&apos;: &apos;William Schultz&apos;, &apos;email&apos;: &apos;william.schultz@mongodb.com&apos;}
&lt;p&gt;Message: Revert &quot;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44771&quot; title=&quot;Allow operations in transactions to safely consult the CatalogCache on mongod&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44771&quot;&gt;&lt;del&gt;SERVER-44771&lt;/del&gt;&lt;/a&gt; Introduce 2nd CatalogCache for filtering only&quot;&lt;/p&gt;

&lt;p&gt;This reverts commit 3473d09fa9b5e418e119941b01c88863744689cc.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/4ae67479e73174a75f2d7141360edb8a8ef90be8&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/4ae67479e73174a75f2d7141360edb8a8ef90be8&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2839910" author="xgen-internal-githook" created="Fri, 7 Feb 2020 17:58:48 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Tommaso Tocci&apos;, &apos;username&apos;: &apos;toto-dev&apos;, &apos;email&apos;: &apos;tommaso.tocci@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44771&quot; title=&quot;Allow operations in transactions to safely consult the CatalogCache on mongod&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44771&quot;&gt;&lt;del&gt;SERVER-44771&lt;/del&gt;&lt;/a&gt; Introduce 2nd CatalogCache for filtering only&lt;/p&gt;

&lt;p&gt;Only on ShardServer (not ReadOnly) use a second catalog cache for&lt;br/&gt;
filtering only in order to allow operations in transactions to safely&lt;br/&gt;
consult the CatalogCache.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/3473d09fa9b5e418e119941b01c88863744689cc&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/3473d09fa9b5e418e119941b01c88863744689cc&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2812130" author="xgen-internal-githook" created="Thu, 6 Feb 2020 16:58:04 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Tommaso Tocci&apos;, &apos;username&apos;: &apos;toto-dev&apos;, &apos;email&apos;: &apos;tommaso.tocci@mongodb.com&apos;}
&lt;p&gt;Message: Revert &quot;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44771&quot; title=&quot;Allow operations in transactions to safely consult the CatalogCache on mongod&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44771&quot;&gt;&lt;del&gt;SERVER-44771&lt;/del&gt;&lt;/a&gt; Introduce 2nd CatalogCache for filtering only&quot;&lt;/p&gt;

&lt;p&gt;This reverts commit 84bdc9478401355656ab7eaec745dbae2e4294cb.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/7a4ea53a34703a51186c9d1ffffa31cf566ef11c&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/7a4ea53a34703a51186c9d1ffffa31cf566ef11c&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2811068" author="xgen-internal-githook" created="Thu, 6 Feb 2020 15:28:06 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;toto-dev&apos;, &apos;name&apos;: &apos;Tommaso Tocci&apos;, &apos;email&apos;: &apos;tommaso.tocci@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-44771&quot; title=&quot;Allow operations in transactions to safely consult the CatalogCache on mongod&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-44771&quot;&gt;&lt;del&gt;SERVER-44771&lt;/del&gt;&lt;/a&gt; Introduce 2nd CatalogCache for filtering only&lt;/p&gt;

&lt;p&gt;Only on ShardServer (not ReadOnly) use a second catalog cache for&lt;br/&gt;
filtering only in order to allow operations in transactions to safely&lt;br/&gt;
consult the CatalogCache.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/84bdc9478401355656ab7eaec745dbae2e4294cb&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/84bdc9478401355656ab7eaec745dbae2e4294cb&lt;/a&gt;&lt;/p&gt;</comment>
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