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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-26788] Running MongoDB on machines with multiple physical cpus</title>
                <link>https://jira.mongodb.org/browse/SERVER-26788</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Hey everyone, we have a production replica set consisting of three nodes that has been running well for two years. It looks like this from a configuration standpoint:&lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;3 m4.2xlarge instances (8 cores)&lt;/li&gt;
	&lt;li&gt;xfs filesystem for data drives&lt;/li&gt;
	&lt;li&gt;ebs volumes (with 8000 provisioned iops &amp;#8211; max for instance type)&lt;/li&gt;
	&lt;li&gt;wired tiger storage engine&lt;/li&gt;
	&lt;li&gt;ssl, auth, etc&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;The performance is great but we want to scale up our nodes to handle a potential spike in usage over the next two weeks. As we are not particularly i/o bound given our usage of MongoDB and appear to be largely cpu bound on these boxes (from what I can tell) we have transitioned these nodes from m4.2xlarge (8 cores) to m4.4xlarge (16 cores).&lt;/p&gt;

&lt;p&gt;To my surprise it &lt;em&gt;appears&lt;/em&gt; as though mongod is only using the first 8 (0-7) of the 16 cores available on this machine. Now, I realize that:&lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;In going from 8 to 16 cores we may now have two physical cpus backing our instance&lt;/li&gt;
	&lt;li&gt;&lt;tt&gt;taskset&lt;/tt&gt; and &lt;tt&gt;cpuset&lt;/tt&gt; can be used to set core/processor affinity and I do not believe they are in use (we are using the init script from the Amazon linux package)&lt;/li&gt;
	&lt;li&gt;numactl should specify that memory usage be interleaved instead of preferring a node or physical cpu (again, confirmed via package init script)&lt;/li&gt;
	&lt;li&gt;Using `htop` as a view onto cpu usage on virtualized hardware is a potentially flawed metric for various reasons&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;So I have the question: &lt;b&gt;Why is mongod appearing to use only 8 of 16 cores available on these boxen?&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;It&apos;s possible that the linux scheduler doesn&apos;t bother scheduling tasks onto the second physical cpu until there are a greater number of running threads so as to take advantage of CPU caches? Right now there is not much load to speak of so that is my current running theory.&lt;/p&gt;

&lt;p&gt;Having never run mognod on a machine having multiple physical cpus in production before I&apos;m only guessing as to what the issue may be. Any clues as to what I might be seeing 10geneers?&lt;/p&gt;</description>
                <environment></environment>
        <key id="327023">SERVER-26788</key>
            <summary>Running MongoDB on machines with multiple physical cpus</summary>
                <type id="6" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Question</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="geert.bosch@mongodb.com">Geert Bosch</assignee>
                                    <reporter username="tyler.brock@gmail.com">Tyler Brock</reporter>
                        <labels>
                    </labels>
                <created>Wed, 26 Oct 2016 17:40:59 +0000</created>
                <updated>Tue, 16 Nov 2021 13:53:24 +0000</updated>
                            <resolved>Sat, 29 Oct 2016 12:10:18 +0000</resolved>
                                    <version>3.2.10</version>
                                                    <component>Concurrency</component>
                                        <votes>0</votes>
                                    <watches>20</watches>
                                                                                                                <comments>
                            <comment id="1421144" author="geert.bosch" created="Fri, 28 Oct 2016 22:48:46 +0000"  >&lt;p&gt;Glad to know things are working for you Tyler! I had looked up the &lt;tt&gt;m2.4xlarge&lt;/tt&gt; on AWS, but it is only listed as &lt;a href=&quot;https://aws.amazon.com/ec2/previous-generation/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;previous generation&lt;/a&gt; option. The &lt;a href=&quot;https://aws.amazon.com/ec2/instance-types/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;main page&lt;/a&gt; explicitly refers to the previous generation page for &lt;tt&gt;m2&lt;/tt&gt; instances. I hope your upgraded system performs according to expectations!&lt;/p&gt;</comment>
                            <comment id="1421142" author="tyler.brock@gmail.com" created="Fri, 28 Oct 2016 22:38:31 +0000"  >&lt;p&gt;Yup, it turns out that once things got cranking the second processor kicked into gear. Thanks again Geert.&lt;/p&gt;</comment>
                            <comment id="1418990" author="tyler.brock@gmail.com" created="Wed, 26 Oct 2016 22:49:05 +0000"  >&lt;p&gt;Thanks Geert! I&apos;ll try that out when traffic dies down tonight but m2.4xlarge definitely has 16vCPUs and M4.2xlarge definitely has 8vCPUs, check it out: &lt;a href=&quot;http://www.ec2instances.info/?cost_duration=monthly&amp;amp;selected=m4.2xlarge,m4.4xlarge&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://www.ec2instances.info/?cost_duration=monthly&amp;amp;selected=m4.2xlarge,m4.4xlarge&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1418888" author="geert.bosch" created="Wed, 26 Oct 2016 21:21:44 +0000"  >&lt;p&gt;There should not be any special configuration required for MongoDB to use all available cores / hyper threads and performance should generally scale well to 16 cores. It looks as if m2.4xlarge is listed as providing only 8 vCpus, while m2.2xlarge has 4vCpus. Not sure why it&apos;s showing up in &lt;tt&gt;top&lt;/tt&gt; the way it does.&lt;br/&gt;
You can run:&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;for (i = 0; i &amp;lt; 1000; i++)&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;    db.benchrun.update({_id: i}, {upsert:1});&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;&amp;nbsp;&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;printjson(benchRun({&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&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;
					&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;    ops: [{&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&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;
					&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;        ns: &quot;db.benchrun&quot;,&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;
					&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;        op: &quot;update&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;   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;        query: {_id: {&quot;#RAND_INT&quot;: [0, 1000]}},&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;        update: {$inc: {x: 1}}&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;
					&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;    }],&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&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;
					&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;    parallel: 16,&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&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;
					&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;    seconds: 20,&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;    host: db.getMongo().host&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;}));&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;db.benchrun.drop();&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;to provide an artificial load that should show all CPUs busy. You might want to check &lt;tt&gt;/proc/cpuinfo&lt;/tt&gt; to see if the number of listed cpus matches expectations.&lt;/p&gt;</comment>
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                            <attachment id="142521" name="htop.png" size="28314" author="tbrock" created="Wed, 26 Oct 2016 17:54:59 +0000"/>
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