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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>[DOCS-12599] Docs for SERVER-16571: Use Actual Memory Constraint vs. Total System Memory When They Differ</title>
                <link>https://jira.mongodb.org/browse/DOCS-12599</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;
&lt;blockquote&gt;
&lt;h3&gt;&lt;a name=&quot;Description%3A&quot;&gt;&lt;/a&gt;Description: &lt;/h3&gt;

&lt;p&gt;We should add a note here: &lt;a href=&quot;https://docs.mongodb.com/manual/core/wiredtiger/#memory-use&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://docs.mongodb.com/manual/core/wiredtiger/#memory-use&lt;/a&gt;&lt;br/&gt;
Which says that if the database has memory limits placed on it which are lower than the system memory, for example when running in a container, then that is used as the maximum RAM available rather than the total system memory.&lt;br/&gt;
We should do something similar anywhere else that we call out memory calculations anywhere else that are used for actions/defaults related to the memory available to MongoDB.&lt;/p&gt;

&lt;p&gt;We should note that the hostInfo command contains a new field, memLimitMB, which tells you if the host is placing any memory usage limit on the process (for example when using containers).&lt;/p&gt;

&lt;p&gt;Note: this work was backported to 4.0 and 3.6.&lt;/p&gt;

&lt;h3&gt;&lt;a name=&quot;EngineeringTicketDescription%3A&quot;&gt;&lt;/a&gt;Engineering Ticket Description:&lt;/h3&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/search?l=C%2B%2B&amp;amp;q=getMemSizeMB&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;The memory size is taken into account within various components today&lt;/a&gt;:&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/217588a5eff6d4c4d2621a03a0cee1b4566e00f1/src/mongo/db/storage/wiredtiger/wiredtiger_util.cpp#L366-L384&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;We set the default WiredTiger cache_size to approximately 1/2 of the memory size&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/217588a5eff6d4c4d2621a03a0cee1b4566e00f1/src/mongo/db/repl/oplog.cpp#L724-L729&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;When ephemeral storage is in use we consider the memory limit in place to determine the default oplog size&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/217588a5eff6d4c4d2621a03a0cee1b4566e00f1/src/mongo/util/tcmalloc_set_parameter.cpp#L140-L144&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;We set the tcmalloc cache size to 1/8th of the available memory&lt;/a&gt;&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;In all of these cases we should take the actual memory constraint that we&apos;re operating under into account rather than the total system memory &amp;#8211; for example when running MongoDB within containers.&lt;/p&gt;&lt;/blockquote&gt;

&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="729010">DOCS-12599</key>
            <summary>Docs for SERVER-16571: Use Actual Memory Constraint vs. Total System Memory When They Differ</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="kay.kim@mongodb.com">Kay Kim</assignee>
                                    <reporter username="kay.kim@mongodb.com">Kay Kim</reporter>
                        <labels>
                            <label>containers</label>
                            <label>docker</label>
                            <label>docs-backport-done</label>
                            <label>kubernetes</label>
                    </labels>
                <created>Wed, 3 Apr 2019 15:25:23 +0000</created>
                <updated>Mon, 13 Nov 2023 18:23:32 +0000</updated>
                            <resolved>Thu, 8 Aug 2019 02:52:23 +0000</resolved>
                                                    <fixVersion>4.1.9</fixVersion>
                    <fixVersion>4.0.9</fixVersion>
                    <fixVersion>3.6.13</fixVersion>
                    <fixVersion>Server_Docs_20231030</fixVersion>
                    <fixVersion>Server_Docs_20231106</fixVersion>
                    <fixVersion>Server_Docs_20231105</fixVersion>
                    <fixVersion>Server_Docs_20231113</fixVersion>
                                    <component>manual</component>
                    <component>Server</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="2362236" author="xgen-internal-githook" created="Thu, 8 Aug 2019 02:52:17 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Kay Kim&apos;, &apos;email&apos;: &apos;kay.kim@10gen.com&apos;, &apos;username&apos;: &apos;kay-kim&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12599&quot; title=&quot;Docs for SERVER-16571: Use Actual Memory Constraint vs. Total System Memory When They Differ&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12599&quot;&gt;&lt;del&gt;DOCS-12599&lt;/del&gt;&lt;/a&gt;: 3.6.13 memlimit&lt;br/&gt;
Branch: v3.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/f45be84e2d7ea6ec6efc719c982c253c1461d862&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/f45be84e2d7ea6ec6efc719c982c253c1461d862&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2362232" author="xgen-internal-githook" created="Thu, 8 Aug 2019 02:47:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Kay Kim&apos;, &apos;email&apos;: &apos;kay.kim@10gen.com&apos;, &apos;username&apos;: &apos;kay-kim&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12599&quot; title=&quot;Docs for SERVER-16571: Use Actual Memory Constraint vs. Total System Memory When They Differ&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12599&quot;&gt;&lt;del&gt;DOCS-12599&lt;/del&gt;&lt;/a&gt;: 4.0.9 memlimit&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/7a5514018b1ea090842e8b2dfbce27cbb32df30e&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/7a5514018b1ea090842e8b2dfbce27cbb32df30e&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2362230" author="xgen-internal-githook" created="Thu, 8 Aug 2019 02:46:17 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Kay Kim&apos;, &apos;email&apos;: &apos;kay.kim@10gen.com&apos;, &apos;username&apos;: &apos;kay-kim&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12599&quot; title=&quot;Docs for SERVER-16571: Use Actual Memory Constraint vs. Total System Memory When They Differ&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12599&quot;&gt;&lt;del&gt;DOCS-12599&lt;/del&gt;&lt;/a&gt;: 4.0.9 memlimit&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/84eed3a52e6642805262f1114a7fd73aaf9e295b&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/84eed3a52e6642805262f1114a7fd73aaf9e295b&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2268225" author="brian.lane" created="Mon, 3 Jun 2019 04:15:34 +0000"  >&lt;p&gt;&lt;a href=&quot;https://docs.mongodb.com/manual/administration/production-notes/index.html&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://docs.mongodb.com/manual/administration/production-notes/index.html&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;Also has a blurb stating:  If you run mongod in a container (e.g. lxc, cgroups, Docker, etc.) that does not have access to all of the RAM available in a system, you must set storage.wiredTiger.engineConfig.cacheSizeGB to a value less than the amount of RAM available in the container. The exact amount depends on the other processes running in the container.&lt;/p&gt;</comment>
                    </comments>
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            <issuekey id="958181">DOCS-13072</issuekey>
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