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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-20057] Concurrent, sharded mapReduces can fail when temporary namespaces collide across mongos processes</title>
                <link>https://jira.mongodb.org/browse/SERVER-20057</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;It&apos;s possible for concurrent, sharded mapReduces to fail with DEAD plan executors when there&apos;s a collision in temporary namespaces across multiple mongos processes.&lt;/p&gt;

&lt;p&gt;This bug is intermittently triggered by the concurrency suite.&lt;/p&gt;

&lt;p&gt;This seems to be the sequence of events:&lt;/p&gt;

&lt;p&gt;1 - A mongos process issues a drop command, on all shards, on a tmp.mrs namespace after finishing the mapReduce.shardedfinish command (in cluster_map_reduce_cmd.cpp).&lt;/p&gt;

&lt;p&gt;2 - At the same time, another mongos process tries to initialize a ParallelSortClusteredCursor on the very same tmp.mrs namespace as part of another mapReduce.shardedfinish command.&lt;/p&gt;

&lt;p&gt;3 - The drop invalidates cursors on the tmp.mrs namespace, which leads to a DEAD plan executor and a failed mapReduce command.&lt;/p&gt;

&lt;hr /&gt;
&lt;p&gt;Relevant log lines:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&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;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 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;I COMMAND  [conn26] CMD: drop db1.tmp.mrs.coll1_1440026655_43&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&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;
					&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;E QUERY    [conn30] Plan executor error during find: DEAD, stats: { stage: &quot;FETCH&quot;, nReturned: 0, executionTimeMillisEstimate: 0, works: 0, advanced: 0, needTime: 0, needYield: 0, saveState: 1, restoreState: 0, isEOF: 0, invalidates: 0, docsExamined: 0, alreadyHasObj: 0, inputStage: { stage: &quot;IXSCAN&quot;, nReturned: 0, executionTimeMillisEstimate: 0, works: 0, advanced: 0, needTime: 0, needYield: 0, saveState: 1, restoreState: 0, isEOF: 0, invalidates: 0, keyPattern: { _id: 1 }, indexName: &quot;_id_&quot;, isMultiKey: false, isUnique: true, isSparse: false, isPartial: false, indexVersion: 1, direction: &quot;forward&quot;, indexBounds: { _id: [ &quot;[MinKey, MaxKey]&quot; ] }, keysExamined: 0, dupsTested: 0, dupsDropped: 0, seenInvalidated: 0 } }&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&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;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 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;I QUERY    [conn30] assertion 17144 Executor error: OperationFailed Operation aborted because: all indexes on collection dropped ns:db1.tmp.mrs.coll1_1440026655_43 query:{ query: {}, orderby: { _id: 1 } }&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;Test output:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&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;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 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;Error: map reduce failed:{&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&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;
					&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;  &quot;ok&quot; : 0,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&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;
					&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;  &quot;errmsg&quot; : &quot;MR post processing failed: { ok: 0.0, errmsg: \&quot;could not initialize cursor across all shards because : Executor error: OperationFailed Operation aborted because: all indexes on collection dropped @...\&quot;, code: 14827 }&quot;&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&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;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 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;}&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;</description>
                <environment></environment>
        <key id="226385">SERVER-20057</key>
            <summary>Concurrent, sharded mapReduces can fail when temporary namespaces collide across mongos processes</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="9">Done</resolution>
                                        <assignee username="backlog-server-sharding">[DO NOT USE] Backlog - Sharding Team</assignee>
                                    <reporter username="kamran.khan">Kamran K.</reporter>
                        <labels>
                            <label>32qa</label>
                    </labels>
                <created>Thu, 20 Aug 2015 01:52:44 +0000</created>
                <updated>Tue, 6 Dec 2022 04:45:47 +0000</updated>
                            <resolved>Mon, 9 Mar 2020 20:26:44 +0000</resolved>
                                    <version>3.1.6</version>
                                    <fixVersion>4.4.0</fixVersion>
                                    <component>MapReduce</component>
                    <component>Sharding</component>
                                        <votes>1</votes>
                                    <watches>9</watches>
                                                                                                                <comments>
                            <comment id="2955493" author="charlie.swanson" created="Mon, 9 Mar 2020 20:26:44 +0000"  >&lt;p&gt;This is no longer a problem after completing a recent project where we created a new implementation of mapReduce backed by the aggregation framework.&lt;/p&gt;</comment>
                            <comment id="1011885" author="xgen-internal-githook" created="Fri, 21 Aug 2015 16:48:29 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;kkmongo&apos;, u&apos;name&apos;: u&apos;Kamran Khan&apos;, u&apos;email&apos;: u&apos;kamran.khan@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-20057&quot; title=&quot;Concurrent, sharded mapReduces can fail when temporary namespaces collide across mongos processes&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-20057&quot;&gt;&lt;del&gt;SERVER-20057&lt;/del&gt;&lt;/a&gt; Disable mapReduce tests in the sharded concurrency suites&lt;/p&gt;

&lt;p&gt;The tests intermittently fail because temporary namespaces can collide&lt;br/&gt;
across mongos processes.  These collisions lead to plan executor errors&lt;br/&gt;
during the mapReduce commands.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/081e8067f7cc39ed57efb6124590d223e49a4595&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/081e8067f7cc39ed57efb6124590d223e49a4595&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
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                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="530352">SERVER-34539</issuekey>
        </issuelink>
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