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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-61427] Unique index builds can cause a loss of availability during commit due to checking many false duplicates</title>
                <link>https://jira.mongodb.org/browse/SERVER-61427</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;While an index build is in progress, we take any concurrent writes and insert them into the side writes table. Once the collection scan and bulk load, we drain the writes from the side writes table into the index. However, it is possible for these concurrent writes to also be seen by the collection scan. In this case, we end up inserting the same index key twice: once during collection scan/bulk load, and once while draining side writes. This is not a correctness issue; for non-unique indexes we simply ignore that the key already exists, and for unique indexes we write down the key as a potential duplicate. For the unique case, we then check all of these false &quot;duplicates&quot; under a MODE_X collection lock before committing the index. This can lead to a loss of availability if the index being built is on a large collection with many writes during the collection scan.&lt;/p&gt;

&lt;p&gt;A couple potential solutions:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Initially check duplicates under a MODE_IX lock and then later use a MODE_X lock, similarly to what we do for draining the side writes table&lt;/li&gt;
	&lt;li&gt;When draining the side writes table for a unique index, if the entire key (including the record id, as opposed to only the key prefix) already exists in the table, do not count as a potential duplicate&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="1923600">SERVER-61427</key>
            <summary>Unique index builds can cause a loss of availability during commit due to checking many false duplicates</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="gregory.noma@mongodb.com">Gregory Noma</assignee>
                                    <reporter username="gregory.noma@mongodb.com">Gregory Noma</reporter>
                        <labels>
                    </labels>
                <created>Thu, 11 Nov 2021 22:22:00 +0000</created>
                <updated>Sun, 29 Oct 2023 21:46:09 +0000</updated>
                            <resolved>Thu, 18 Nov 2021 15:35:23 +0000</resolved>
                                    <version>4.2.0</version>
                    <version>4.4.0</version>
                    <version>5.0.0</version>
                                    <fixVersion>5.2.0</fixVersion>
                    <fixVersion>5.1.2</fixVersion>
                    <fixVersion>5.0.6</fixVersion>
                    <fixVersion>4.4.11</fixVersion>
                    <fixVersion>4.2.18</fixVersion>
                                                        <votes>0</votes>
                                    <watches>17</watches>
                                                                                                                <comments>
                            <comment id="4230574" author="xgen-internal-githook" created="Fri, 3 Dec 2021 21:30:15 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Gregory Noma&apos;, &apos;email&apos;: &apos;gregory.noma@gmail.com&apos;, &apos;username&apos;: &apos;gregorynoma&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61427&quot; title=&quot;Unique index builds can cause a loss of availability during commit due to checking many false duplicates&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61427&quot;&gt;&lt;del&gt;SERVER-61427&lt;/del&gt;&lt;/a&gt; Skip duplicate index key handler when exact key already exists in index&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a)&lt;br/&gt;
(cherry picked from commit cbfe08edee4a6aa41694b73be690b4e56de0bb3a)&lt;br/&gt;
(cherry picked from commit e729f76f2c5de716e0724651e14a51b7e424258a)&lt;br/&gt;
Branch: v4.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/c797110b90fd5d950fa5d78aa26ae198c76883c6&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/c797110b90fd5d950fa5d78aa26ae198c76883c6&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4228032" author="xgen-internal-githook" created="Thu, 2 Dec 2021 20:12:17 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Gregory Noma&apos;, &apos;email&apos;: &apos;gregory.noma@gmail.com&apos;, &apos;username&apos;: &apos;gregorynoma&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61427&quot; title=&quot;Unique index builds can cause a loss of availability during commit due to checking many false duplicates&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61427&quot;&gt;&lt;del&gt;SERVER-61427&lt;/del&gt;&lt;/a&gt; Skip duplicate index key handler when exact key already exists in index&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a)&lt;br/&gt;
(cherry picked from commit cbfe08edee4a6aa41694b73be690b4e56de0bb3a)&lt;br/&gt;
Branch: v4.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/e729f76f2c5de716e0724651e14a51b7e424258a&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/e729f76f2c5de716e0724651e14a51b7e424258a&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4224992" author="xgen-internal-githook" created="Wed, 1 Dec 2021 18:17:46 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Gregory Noma&apos;, &apos;email&apos;: &apos;gregory.noma@gmail.com&apos;, &apos;username&apos;: &apos;gregorynoma&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61427&quot; title=&quot;Unique index builds can cause a loss of availability during commit due to checking many false duplicates&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61427&quot;&gt;&lt;del&gt;SERVER-61427&lt;/del&gt;&lt;/a&gt; Skip duplicate index key handler when exact key already exists in index&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a)&lt;br/&gt;
(cherry picked from commit cbfe08edee4a6aa41694b73be690b4e56de0bb3a)&lt;br/&gt;
Branch: v5.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/52e9e4fe03089c106a7c91206256c55631829a25&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/52e9e4fe03089c106a7c91206256c55631829a25&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4224582" author="xgen-internal-githook" created="Wed, 1 Dec 2021 16:26:56 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Gregory Noma&apos;, &apos;email&apos;: &apos;gregory.noma@gmail.com&apos;, &apos;username&apos;: &apos;gregorynoma&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61427&quot; title=&quot;Unique index builds can cause a loss of availability during commit due to checking many false duplicates&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61427&quot;&gt;&lt;del&gt;SERVER-61427&lt;/del&gt;&lt;/a&gt; Skip duplicate index key handler when exact key already exists in index&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a)&lt;br/&gt;
Branch: v5.1&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/cbfe08edee4a6aa41694b73be690b4e56de0bb3a&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/cbfe08edee4a6aa41694b73be690b4e56de0bb3a&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4197390" author="bruce.lucas@10gen.com" created="Thu, 18 Nov 2021 13:29:02 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=harshad.dhavale&quot; class=&quot;user-hover&quot; rel=&quot;harshad.dhavale&quot;&gt;harshad.dhavale&lt;/a&gt;, I opened backport requests back to 4.2.&lt;/p&gt;</comment>
                            <comment id="4196581" author="xgen-internal-githook" created="Wed, 17 Nov 2021 23:51:17 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Gregory Noma&apos;, &apos;email&apos;: &apos;gregory.noma@gmail.com&apos;, &apos;username&apos;: &apos;gregorynoma&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-61427&quot; title=&quot;Unique index builds can cause a loss of availability during commit due to checking many false duplicates&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-61427&quot;&gt;&lt;del&gt;SERVER-61427&lt;/del&gt;&lt;/a&gt; Skip duplicate index key handler when exact key already exists in index&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/9f15b2b1eeb356f4e3d0c6e06302941ec685cc0a&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
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                                        <issuelink>
            <issuekey id="1927871">SERVER-61582</issuekey>
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