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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-49941] Handle writes (updates and removes) during tenant migrations that do not generate oplog entries because they were a no-op</title>
                <link>https://jira.mongodb.org/browse/SERVER-49941</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;If a write does not generate an oplog entry, it must be because any earlier writes this write depends on is already reflected in the data (&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=lingzhi.deng&quot; class=&quot;user-hover&quot; rel=&quot;lingzhi.deng&quot;&gt;lingzhi.deng&lt;/a&gt; , could you confirm?).&lt;/p&gt;

&lt;p&gt;This means any writes this write depends on must have been assigned an OpTime earlier than blockTimestamp, at least on this primary&apos;s branch of history.&lt;/p&gt;

&lt;p&gt;If the write came with w:majority, the write will wait for the system last OpTime to be majority committed, which must include the blockTimestamp. So, if the migration commits, the write is guaranteed to be reflected on the recipient.&lt;/p&gt;

&lt;p&gt;If the write came with w &amp;lt; majority, the write is not guaranteed to be reflected in the database anyway, so it is ok if it is not reflected on the recipient.&lt;/p&gt;

&lt;p&gt;So, there should be no need to do anything special for such writes, though &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=jack.mulrow&quot; class=&quot;user-hover&quot; rel=&quot;jack.mulrow&quot;&gt;jack.mulrow&lt;/a&gt;, it may be good to confirm that causal consistency will be respected for such writes.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1422551">SERVER-49941</key>
            <summary>Handle writes (updates and removes) during tenant migrations that do not generate oplog entries because they were a no-op</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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="jack.mulrow@mongodb.com">Jack Mulrow</assignee>
                                    <reporter username="cheahuychou.mao@mongodb.com">Cheahuychou Mao</reporter>
                        <labels>
                            <label>pm-1791_milestone-A</label>
                    </labels>
                <created>Tue, 28 Jul 2020 02:41:12 +0000</created>
                <updated>Sun, 29 Oct 2023 22:05:07 +0000</updated>
                            <resolved>Wed, 17 Mar 2021 16:35:13 +0000</resolved>
                                                    <fixVersion>4.9.0</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="3669322" author="xgen-internal-githook" created="Wed, 17 Mar 2021 16:22:24 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Jack Mulrow&apos;, &apos;email&apos;: &apos;jack.mulrow@mongodb.com&apos;, &apos;username&apos;: &apos;jsmulrow&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-49941&quot; title=&quot;Handle writes (updates and removes) during tenant migrations that do not generate oplog entries because they were a no-op&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-49941&quot;&gt;&lt;del&gt;SERVER-49941&lt;/del&gt;&lt;/a&gt; Add core test for no-op writes&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/6cc9d99708e73f736c9af13ab4f04f0ef5594aff&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/6cc9d99708e73f736c9af13ab4f04f0ef5594aff&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3660536" author="lingzhi.deng" created="Thu, 11 Mar 2021 21:33:49 +0000"  >&lt;p&gt;Just want to point out something very subtle here: it is not always correct to return lastApplied as the operationTime for noop writes because of the issue described in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-39364&quot; title=&quot;Audit uses of setLastOpToSystemLastOpTime&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-39364&quot;&gt;&lt;del&gt;SERVER-39364&lt;/del&gt;&lt;/a&gt;. If a write becomes a no-op because of a concurrent write, the lastApplied could be stale because the update to the lastApplied is in an on-commit hook after the data changes are made. So in that case, we would instead hit &lt;a href=&quot;https://github.com/mongodb/mongo/blob/e2dd9ca37c/src/mongo/db/service_entry_point_common.cpp#L497&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this&lt;/a&gt; which should return the lastOp of the client and that should be set to &lt;a href=&quot;https://github.com/mongodb/mongo/blob/558bef726dc857223d672e552601668f3d6f4cd3/src/mongo/db/repl/repl_client_info.cpp#L72&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;the timestamp of the last oplog entry&lt;/a&gt; in the oplog. But yes, the operationTime should be&#160;inclusive of the earlier operation that performed the same modification.&lt;/p&gt;</comment>
                            <comment id="3660162" author="jack.mulrow" created="Thu, 11 Mar 2021 20:17:00 +0000"  >&lt;p&gt;As for respecting causal consistency, the operationTime in the response for a noop write will always be inclusive of the earlier operation that already performed its modification to the data (it would be set to the ReplicationCoordinator&apos;s last applied opTime &lt;a href=&quot;https://github.com/mongodb/mongo/blob/e2dd9ca37c/src/mongo/db/service_entry_point_common.cpp#L509&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;&#160;after executing), so any subsequent afterClusterTime reads should correctly interact with the migration like any other read with afterClusterTime.&lt;/p&gt;</comment>
                            <comment id="3508424" author="lingzhi.deng" created="Mon, 30 Nov 2020 15:59:57 +0000"  >&lt;p&gt;I think so. I think if an user write becomes an noop, it means the same modification to the data was already performed by an earlier operation.&lt;/p&gt;</comment>
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