<!-- 
RSS generated by JIRA (9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66) at Thu Feb 08 06:37:19 UTC 2024

It is possible to restrict the fields that are returned in this document by specifying the 'field' parameter in your request.
For example, to request only the issue key and summary append 'field=key&field=summary' to the URL of your request.
-->
<rss version="0.92" >
<channel>
    <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>[SERVER-78050] Chunk Migration Can Lose Data If Processing Deferred Modifications</title>
                <link>https://jira.mongodb.org/browse/SERVER-78050</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;If a update is performed in a transaction, we can&apos;t immediately read back the document if we don&apos;t already have the post-image, so we instead &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source.cpp#L292-L299&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;insert it into a list of deferred updates&lt;/a&gt;. These deferred updates will be &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source.cpp#L896&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;processed in nextModBatch&lt;/a&gt; by &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source.cpp#L880&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;reading the latest version of the document&lt;/a&gt; when the recipient shard calls &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source_legacy_commands.cpp#L244&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;_transferMods&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;Next, the ids of the documents that have changed will be &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source.cpp#L913&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;pulled from the update list&lt;/a&gt;, and those &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/s/migration_chunk_cloner_source.cpp#L927&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;documents will be read&lt;/a&gt; in order to get the latest state to transfer to the recipient.&lt;/p&gt;

&lt;p&gt;However, if we have already read documents while processing the deferred updates, a snapshot will be opened and pinned to the operation context, continuing to be used when we read later to get the latest state of the documents in the update list.&lt;/p&gt;

&lt;p&gt;This means that it is possible for an update to read from a stale snapshot during the following sequence of events:&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;Deferred updates are processed, a snapshot is opened&lt;/li&gt;
	&lt;li&gt;Another thread updates a document in the chunk being moved, adding its id to the update list&lt;/li&gt;
	&lt;li&gt;The updates list is spliced in nextModsBatch&lt;/li&gt;
	&lt;li&gt;The state of the documents in the updates list is read using the same snapshot as in step 1, prior to the update being made in step 2&lt;/li&gt;
	&lt;li&gt;The update is lost&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;Calling &lt;a href=&quot;https://github.com/mongodb/mongo/blob/46ab5002b1bce2da7fc2a86dc98b8a6fa7fb0f9c/src/mongo/db/storage/recovery_unit.h#L254-L263&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;abandonSnapshot&lt;/a&gt; on the operation context&apos;s recovery unit after splicing the update list should be sufficient to ensure that we will read from a snapshot at least as recent as the updates in the list, though it&apos;s not clear if this is the best long term solution to the problem.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2367147">SERVER-78050</key>
            <summary>Chunk Migration Can Lose Data If Processing Deferred Modifications</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="2" iconUrl="https://jira.mongodb.org/images/icons/priorities/critical.svg">Critical - P2</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="brett.nawrocki@mongodb.com">Brett Nawrocki</assignee>
                                    <reporter username="brett.nawrocki@mongodb.com">Brett Nawrocki</reporter>
                        <labels>
                            <label>sharding-nyc-subteam1</label>
                    </labels>
                <created>Tue, 13 Jun 2023 18:48:01 +0000</created>
                <updated>Sun, 29 Oct 2023 21:20:06 +0000</updated>
                            <resolved>Thu, 15 Jun 2023 22:22:55 +0000</resolved>
                                    <version>4.4.19</version>
                    <version>5.0.15</version>
                    <version>6.3.0-rc0</version>
                    <version>6.0.5</version>
                    <version>7.1.0-rc0</version>
                    <version>7.0.0-rc4</version>
                                    <fixVersion>7.1.0-rc0</fixVersion>
                    <fixVersion>6.0.7</fixVersion>
                    <fixVersion>5.0.19</fixVersion>
                    <fixVersion>4.4.23</fixVersion>
                    <fixVersion>7.0.0-rc4</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="5503814" author="xgen-internal-githook" created="Fri, 16 Jun 2023 01:50:22 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Brett Nawrocki&apos;, &apos;email&apos;: &apos;brett.nawrocki@mongodb.com&apos;, &apos;username&apos;: &apos;brettnawrocki&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-78050&quot; title=&quot;Chunk Migration Can Lose Data If Processing Deferred Modifications&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-78050&quot;&gt;&lt;del&gt;SERVER-78050&lt;/del&gt;&lt;/a&gt; Ensure _transferMods reads from latest snapshot&lt;/p&gt;

&lt;p&gt;(cherry picked from commit e015af264b295b9266b0ddf0197cb4da3c3fa0fd)&lt;br/&gt;
Branch: v5.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/916bc197e430da7bc73fcfe20f9a712b253d7558&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/916bc197e430da7bc73fcfe20f9a712b253d7558&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5503809" author="xgen-internal-githook" created="Fri, 16 Jun 2023 01:40:18 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Brett Nawrocki&apos;, &apos;email&apos;: &apos;brett.nawrocki@mongodb.com&apos;, &apos;username&apos;: &apos;brettnawrocki&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-78050&quot; title=&quot;Chunk Migration Can Lose Data If Processing Deferred Modifications&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-78050&quot;&gt;&lt;del&gt;SERVER-78050&lt;/del&gt;&lt;/a&gt; Ensure _transferMods reads from latest snapshot&lt;/p&gt;

&lt;p&gt;(cherry picked from commit e015af264b295b9266b0ddf0197cb4da3c3fa0fd)&lt;br/&gt;
Branch: v4.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/173959ef72626005fe213f606d9e6e8fa26843b2&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/173959ef72626005fe213f606d9e6e8fa26843b2&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5503507" author="xgen-internal-githook" created="Thu, 15 Jun 2023 22:46:50 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Brett Nawrocki&apos;, &apos;email&apos;: &apos;brett.nawrocki@mongodb.com&apos;, &apos;username&apos;: &apos;brettnawrocki&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-78050&quot; title=&quot;Chunk Migration Can Lose Data If Processing Deferred Modifications&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-78050&quot;&gt;&lt;del&gt;SERVER-78050&lt;/del&gt;&lt;/a&gt; Ensure _transferMods reads from latest snapshot&lt;/p&gt;

&lt;p&gt;(cherry picked from commit e015af264b295b9266b0ddf0197cb4da3c3fa0fd)&lt;br/&gt;
Branch: v6.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/9baeeaf3792c8d656cfab7df3035d467ecd2ebad&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/9baeeaf3792c8d656cfab7df3035d467ecd2ebad&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5503394" author="xgen-internal-githook" created="Thu, 15 Jun 2023 22:08:00 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Brett Nawrocki&apos;, &apos;email&apos;: &apos;brett.nawrocki@mongodb.com&apos;, &apos;username&apos;: &apos;brettnawrocki&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-78050&quot; title=&quot;Chunk Migration Can Lose Data If Processing Deferred Modifications&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-78050&quot;&gt;&lt;del&gt;SERVER-78050&lt;/del&gt;&lt;/a&gt; Ensure _transferMods reads from latest snapshot&lt;/p&gt;

&lt;p&gt;(cherry picked from commit e015af264b295b9266b0ddf0197cb4da3c3fa0fd)&lt;br/&gt;
Branch: v7.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/634d301f10ef860dc6de0dacb92a23751c3d6a12&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/634d301f10ef860dc6de0dacb92a23751c3d6a12&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5502696" author="xgen-internal-githook" created="Thu, 15 Jun 2023 18:28:41 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Brett Nawrocki&apos;, &apos;email&apos;: &apos;brett.nawrocki@mongodb.com&apos;, &apos;username&apos;: &apos;brettnawrocki&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-78050&quot; title=&quot;Chunk Migration Can Lose Data If Processing Deferred Modifications&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-78050&quot;&gt;&lt;del&gt;SERVER-78050&lt;/del&gt;&lt;/a&gt; Ensure _transferMods reads from latest snapshot&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/e015af264b295b9266b0ddf0197cb4da3c3fa0fd&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/e015af264b295b9266b0ddf0197cb4da3c3fa0fd&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10420">
                    <name>Backports</name>
                                            <outwardlinks description="backported by">
                                                        </outwardlinks>
                                                        </issuelinktype>
                            <issuelinktype id="10011">
                    <name>Depends</name>
                                                                <inwardlinks description="is depended on by">
                                                        </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10520">
                    <name>Problem/Incident</name>
                                            <outwardlinks description="causes">
                                                        </outwardlinks>
                                                                <inwardlinks description="is caused by">
                                        <issuelink>
            <issuekey id="2179546">SERVER-71219</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                    </issuelinks>
                <attachments>
                    </attachments>
                <subtasks>
                    </subtasks>
                <customfields>
                                                <customfield id="customfield_10050" key="com.atlassian.jira.toolkit:comments">
                        <customfieldname># Replies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>5.0</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_18555" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname># of Sprints</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1.0</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                <customfield id="customfield_12450" key="com.atlassian.jira.plugin.system.customfieldtypes:multicheckboxes">
                        <customfieldname>Backport Requested</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="25578"><![CDATA[v7.0]]></customfieldvalue>
    
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10011" key="com.atlassian.jira.plugin.system.customfieldtypes:radiobuttons">
                        <customfieldname>Backwards Compatibility</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="10038"><![CDATA[Fully Compatible]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                            <customfield id="customfield_10055" key="com.atlassian.jira.ext.charting:firstresponsedate">
                        <customfieldname>Date of 1st Reply</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>Thu, 15 Jun 2023 15:15:24 +0000</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10052" key="com.atlassian.jira.toolkit:dayslastcommented">
                        <customfieldname>Days since reply</customfieldname>
                        <customfieldvalues>
                                        33 weeks, 6 days ago
    
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_18254" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Dependencies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue><![CDATA[]]></customfieldvalue>


                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_15850" key="com.atlassian.jira.plugins.jira-development-integration-plugin:devsummary">
                        <customfieldname>Development</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                        <customfield id="customfield_17050" key="com.atlassian.jira.plugin.system.customfieldtypes:radiobuttons">
                        <customfieldname>Downstream Team Attention</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="16941"><![CDATA[Not Needed]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                <customfield id="customfield_10057" key="com.atlassian.jira.toolkit:lastusercommented">
                        <customfieldname>Last comment by Customer</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>true</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_10056" key="com.atlassian.jira.toolkit:lastupdaterorcommenter">
                        <customfieldname>Last commenter</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>luke.bonanomi@mongodb.com</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_11151" key="com.atlassian.jira.toolkit:LastCommentDate">
                        <customfieldname>Last public comment date</customfieldname>
                        <customfieldvalues>
                            33 weeks, 6 days ago
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_16465" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Linked BF Score</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>135.0</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                        <customfield id="customfield_10032" key="com.atlassian.jira.plugin.system.customfieldtypes:select">
                        <customfieldname>Operating System</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="10026"><![CDATA[ALL]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                <customfield id="customfield_10051" key="com.atlassian.jira.toolkit:participants">
                        <customfieldname>Participants</customfieldname>
                        <customfieldvalues>
                                        <customfieldvalue>brett.nawrocki@mongodb.com</customfieldvalue>
            <customfieldvalue>xgen-internal-githook</customfieldvalue>
    
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                        <customfield id="customfield_14254" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Product Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|i2doo7:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                <customfield id="customfield_12550" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>2|i1vwa8:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10558" key="com.pyxis.greenhopper.jira:gh-global-rank">
                        <customfieldname>Rank (Obsolete)</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>9223372036854775807</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_23361" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Requested By</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                            <customfield id="customfield_22250" key="com.atlassian.jira.plugin.system.customfieldtypes:radiobuttons">
                        <customfieldname>Special Downgrade Instructions Required</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="23343"><![CDATA[Not Needed]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10557" key="com.pyxis.greenhopper.jira:gh-sprint">
                        <customfieldname>Sprint</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue id="7363">Sharding NYC 2023-06-26</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                        <customfield id="customfield_10053" key="com.atlassian.jira.ext.charting:timeinstatus">
                        <customfieldname>Time In Status</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                        <customfield id="customfield_22870" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Triagers</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                    <customfield id="customfield_14350" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>serverRank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|i2datj:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                    </customfields>
    </item>
</channel>
</rss>