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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-12545] Everything stopped after adding hashed index</title>
                <link>https://jira.mongodb.org/browse/SERVER-12545</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;After creating a new index to prepare for sharding, everything seemed to stop and afterwards new warnings started to show up in the logs that we haven&apos;t seen before.&lt;/p&gt;

&lt;p&gt;The index was created like this:&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;   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;db.visits.ensureIndex({&quot;visited&quot;: &quot;hashed&quot;}, {background: true})&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;The cli froze until it was done building the index. The MMS statistics shows 150% lock for the period (how can you have more than 100?). Then when the lock went down again, our application stopped working and a large spike of connections was created.&lt;/p&gt;

&lt;p&gt;After restarting all mongos clients it seemed to resume operation again.&lt;/p&gt;

&lt;p&gt;Now we are observing these kinds of warnings in the logs:&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;   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;warning: ClientCursor::yield can&apos;t unlock b/c of recursive lock ns: api.visits top: { opid: 1445932706, active: true, secs_running: 0, op: &quot;query&quot;, ns: &quot;api.visits&quot;, query: { findAndModify: &quot;visits&quot;, new: true, fields: { _id: 1 }, query: { ... }, update: { ... }, ...&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;While no index was removed or modified, only this new index was added, no queries was changed. And doing &lt;tt&gt;explain()&lt;/tt&gt; on the query presented in the &lt;tt&gt;findAndModify&lt;/tt&gt; shows that it is still using a fast index that was there since before.&lt;/p&gt;

&lt;p&gt;Why did we get this behaviour and how do we create indexes in the future without having to let everything go to pieces? Do we have to worry about this warning?&lt;/p&gt;</description>
                <environment>Ubuntu 12.04</environment>
        <key id="108338">SERVER-12545</key>
            <summary>Everything stopped after adding hashed index</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="ramon.fernandez@mongodb.com">Ramon Fernandez Marina</assignee>
                                    <reporter username="balboah">Johnny Boy</reporter>
                        <labels>
                    </labels>
                <created>Thu, 30 Jan 2014 11:27:45 +0000</created>
                <updated>Wed, 10 Dec 2014 23:10:14 +0000</updated>
                            <resolved>Thu, 3 Jul 2014 15:16:54 +0000</resolved>
                                    <version>2.4.9</version>
                                                    <component>Index Maintenance</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="647418" author="ramon.fernandez" created="Thu, 3 Jul 2014 15:16:14 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=balboah&quot; class=&quot;user-hover&quot; rel=&quot;balboah&quot;&gt;balboah&lt;/a&gt;, since we haven&apos;t heard back from you we&apos;re going to mark this issue as resolved. If you&apos;re still seeing the &lt;tt&gt;ClientCursor::yield warnings&lt;/tt&gt;, please feel free to re-open the ticket and provide the output of &lt;tt&gt;db.currentOp()&lt;/tt&gt; when the warnings appear.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
                            <comment id="635255" author="ramon.fernandez" created="Thu, 26 Jun 2014 18:12:24 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=balboah&quot; class=&quot;user-hover&quot; rel=&quot;balboah&quot;&gt;balboah&lt;/a&gt;, we haven&apos;t heard back from you for some time. If this is still an issue for you, can you please send us the output of &lt;tt&gt;db.currentOp()&lt;/tt&gt; when you see &lt;tt&gt;ClientCursor::yield&lt;/tt&gt; warnings?&lt;/p&gt;

&lt;p&gt;Thanks,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
                            <comment id="611972" author="ramon.fernandez" created="Fri, 6 Jun 2014 23:02:52 +0000"  >&lt;p&gt;When creating indexes from the mongo shell, &lt;a href=&quot;http://docs.mongodb.org/manual/core/index-creation/#behavior&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;the session will block until the index build is complete&lt;/a&gt;, even if {&lt;tt&gt;background:true&lt;/tt&gt;} is specified.&lt;/p&gt;

&lt;p&gt;As for the warnings in the logs, can you send us the output of &lt;tt&gt;db.currentOp()&lt;/tt&gt; when you see the warnings?&lt;/p&gt;</comment>
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