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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-75806] analyzeShardKey command can fail with readConcern afterClusterTime error</title>
                <link>https://jira.mongodb.org/browse/SERVER-75806</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The step for calculating the read and write distribution metrics in the analyzeShardKey command works as follows:&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;The client runs the analyzeShardKey command against some mongos. That mongos forwards the command to a random shard with readPreference &quot;secondaryPreferred&quot;.&lt;/li&gt;
	&lt;li&gt;The shardsvr node running the analyzeShardKey command generates the split points for the shard key being analyzed, and then persists them in the config.analyzeShardKeySplitPoints collection. If the node isn&apos;t a primary, it would run the insert command against the primary node using ScopedClientConnection (&lt;a href=&quot;https://github.com/mongodb/mongo/blob/2a994ea0779acb7f594d2a23e96e6e3affbb8b8b/src/mongo/s/analyze_shard_key_util.cpp#L103&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;).&#160;&lt;/li&gt;
	&lt;li&gt;The shardsvr node then sends an aggregate command with the $_analyzeShardKeyReadWriteDistribution stage to all shards that own chunks for the collection. The stage has the following spec, where &apos;splitPointsAfterClusterTime&apos; is set to the operationTime in the response for insert command in step 2, and &apos;splitPointsShardId&apos; set to its own shard id.
&lt;p/&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;     splitPointsFilter: &amp;lt;object&amp;gt;&lt;/span&gt;&lt;/pre&gt;
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						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;     splitPointsAfterClusterTime: &amp;lt;timestamp&amp;gt;,&lt;/span&gt;&lt;/pre&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
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&lt;p/&gt;&lt;/li&gt;
	&lt;li&gt;Each shard running the $_analyzeShardKeyReadWriteDistribution stage then runs an aggregate command against the shard &apos;splitPointsShardId&apos; to fetch all split point documents. The aggregate command has a $match stage with filter set to &apos;splitPointsFilter&apos; and readConcern with afterClusterTime set to &apos;splitPointsAfterClusterTime&apos;. Using the split ponits, each shard then creates a synthetic routing table and does metrics calculation.&#160;&lt;/li&gt;
	&lt;li&gt;The shardsvr node from step 1 combines the metrics from all the shards.&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;It turns out the use of ScopedClientConnection can result in some causal consistency issue in the case where the analyzeShardKey targets a secondary node, since ScopedClientConnection doesn&apos;t internally have a VectorClockMetadataHook (e.g. like &lt;a href=&quot;https://github.com/10gen/mongo/blob/0c433543d0a0feea99d61c231c6e50758b098840/src/mongo/s/mongos_main.cpp#L444-L445&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;) which would &lt;a href=&quot;https://github.com/mongodb/mongo/blob/2a994ea0779acb7f594d2a23e96e6e3affbb8b8b/src/mongo/db/vector_clock_metadata_hook.cpp#L73-L74&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;read the clusterTime of every reply and advance the VectorClock&lt;/a&gt;. That is, if the inserts do not replicated to the node running the analyzeShardKey before the $_analyzeShardKeyReadWriteDistribution aggregate commands are sent out in step 3, the $match aggregate command against the config.analyzeShardKeySplitPoints collection can arrive with clusterTime less than the afterClusterTime in the command itself. If at that point the node the $match aggregation is running also hasn&apos;t replicated the inserts in step 2, then the command would fail &lt;a href=&quot;https://github.com/10gen/mongo/blob/ccddcca1fc6bf5f2c9f7012c74dd216a35e8d580/src/mongo/db/read_concern_mongod.cpp#L372-L377&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt; and this would cause the analyzeShardKey as a whole to fail.&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="2308994">SERVER-75806</key>
            <summary>analyzeShardKey command can fail with readConcern afterClusterTime error</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="cheahuychou.mao@mongodb.com">Cheahuychou Mao</assignee>
                                    <reporter username="cheahuychou.mao@mongodb.com">Cheahuychou Mao</reporter>
                        <labels>
                    </labels>
                <created>Thu, 6 Apr 2023 18:14:15 +0000</created>
                <updated>Sun, 29 Oct 2023 21:23:27 +0000</updated>
                            <resolved>Mon, 10 Apr 2023 20:13:56 +0000</resolved>
                                                    <fixVersion>7.0.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="5336244" author="xgen-internal-githook" created="Mon, 10 Apr 2023 20:08:00 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Cheahuychou Mao&apos;, &apos;email&apos;: &apos;mao.cheahuychou@gmail.com&apos;, &apos;username&apos;: &apos;cheahuychou&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-75806&quot; title=&quot;analyzeShardKey command can fail with readConcern afterClusterTime error&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-75806&quot;&gt;&lt;del&gt;SERVER-75806&lt;/del&gt;&lt;/a&gt; Make the analyzeShardKey machinery run commands via the ReplicaSetNodeProcessInterface executor or Grid fixed executor&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/b48396832c7c1fa5c9b903b86852e63822cb17ef&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/b48396832c7c1fa5c9b903b86852e63822cb17ef&lt;/a&gt;&lt;/p&gt;</comment>
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