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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-29868] swap keeps growing up even though there are a plenty of available RAM</title>
                <link>https://jira.mongodb.org/browse/SERVER-29868</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;We have a Mongodb sharded cluster consisting of one router server, one config server and two shard servers. The swap space in the shard servers keeps growing up even though there are plenty of available RAM. The speed is about tens of megabyte a week.&lt;/p&gt;

&lt;p&gt;System of shard server:&lt;br/&gt;
operating system: Ubuntu 16, &lt;br/&gt;
CPU: 4 core 3.4GHZ, &lt;br/&gt;
RAM:16GB, &lt;br/&gt;
database: Mongodb 3.4.2 Community version&lt;/p&gt;

&lt;p&gt;There is no error in the Mongodb log file. The swap space in router and config server are always zero.&lt;br/&gt;
Please let me know anything else you need. I appreciate your support so much!&lt;/p&gt;

&lt;p&gt;John Wang&lt;/p&gt;</description>
                <environment></environment>
        <key id="398402">SERVER-29868</key>
            <summary>swap keeps growing up even though there are a plenty of available RAM</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="mark.agarunov">Mark Agarunov</assignee>
                                    <reporter username="John_Wang">John Wang [X]</reporter>
                        <labels>
                    </labels>
                <created>Tue, 27 Jun 2017 05:38:56 +0000</created>
                <updated>Wed, 2 Aug 2017 21:51:43 +0000</updated>
                            <resolved>Wed, 28 Jun 2017 19:41:58 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="1639161" author="john_wang" created="Wed, 2 Aug 2017 21:51:43 +0000"  >&lt;p&gt;Hi Ramon,&lt;/p&gt;

&lt;p&gt;  Thanks for your update so much!&lt;/p&gt;

&lt;p&gt;Best Regards,&lt;/p&gt;

&lt;p&gt;John Wang&lt;/p&gt;</comment>
                            <comment id="1639108" author="ramon.fernandez" created="Wed, 2 Aug 2017 21:01:35 +0000"  >&lt;p&gt;The contents of &lt;tt&gt;diagnostic.data&lt;/tt&gt; is &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-26312?focusedCommentId=1394315&amp;amp;page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1394315&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;explained in this comment&lt;/a&gt;, which also points to the source code if you&apos;re interested about the details of the format (which is specially formatted and compressed).&lt;/p&gt;

&lt;p&gt;Unfortunately I&apos;m not aware of any publicly available tools to read and parse the output of the &lt;tt&gt;diagnostic.data&lt;/tt&gt;, but the details are public so a tool can be written for it.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
                            <comment id="1610714" author="john_wang" created="Thu, 29 Jun 2017 18:37:09 +0000"  >&lt;p&gt;Hi Mark,&lt;/p&gt;

&lt;p&gt;I agree with your point. Most of the swap space are used by Mongodb. I think probably the kernel swaps lots of old mapping files of Mongodb.&lt;br/&gt;
What tool can read the diagnostic.data file?&lt;br/&gt;
Thanks for your support so much!&lt;/p&gt;

&lt;p&gt;John Wang &lt;/p&gt;</comment>
                            <comment id="1609051" author="mark.agarunov" created="Wed, 28 Jun 2017 19:41:44 +0000"  >&lt;p&gt;Hello &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=John_Wang&quot; class=&quot;user-hover&quot; rel=&quot;John_Wang&quot;&gt;John_Wang&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;Thank you for providing this data. Looking over this, I don&apos;t believe the swap usage is related to mongod itself. This is likely the linux kernel just swapping memory that hasn&apos;t been recently accessed. The kernel will generally not fill swap to the point of causing an out of memory condition, however you could try to set the vm.swapiness value lower &lt;a href=&quot;https://help.ubuntu.com/community/SwapFaq/#What_is_swappiness_and_how_do_I_change_it.3F&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;(Ubuntu recommends 10 for servers)&lt;/a&gt;, which should cause the system to only use swap when needed, and not swap out infrequently accessed pages. &lt;/p&gt;

&lt;p&gt;Please note that SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the &lt;a href=&quot;http://groups.google.com/group/mongodb-user&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;mongodb-user group&lt;/a&gt; or &lt;a href=&quot;http://stackoverflow.com/questions/tagged/mongodb&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;Stack Overflow with the &lt;tt&gt;mongodb&lt;/tt&gt; tag&lt;/a&gt;. A question like this involving more discussion would be best posted on the mongodb-user group.&lt;/p&gt;

&lt;p&gt;Thanks,&lt;br/&gt;
Mark&lt;/p&gt;</comment>
                            <comment id="1608304" author="john_wang" created="Wed, 28 Jun 2017 03:20:42 +0000"  >&lt;p&gt;Hi Mark,&lt;/p&gt;

&lt;p&gt;I appreciate your support so much!&lt;br/&gt;
The vm.swapiness value is 60 that is the default value in Ubuntu.&lt;br/&gt;
I uploaded the two diagnostic.data.1&amp;amp;2.rar files.  What tools can read the diagnostic.data? Thanks for your time.&lt;br/&gt;
We have 1000 clients keep writing about 3MB/minute data into the Mongodb cluster. If the swap keeps going until full, is it possible to cause memory leak in the shard server cause there is no more space to swap?&lt;/p&gt;

&lt;p&gt;Please let me know anything you need. Thanks so much!&lt;/p&gt;

&lt;p&gt;Best,&lt;/p&gt;

&lt;p&gt;John Wang&lt;/p&gt;</comment>
                            <comment id="1608293" author="john_wang" created="Wed, 28 Jun 2017 03:03:54 +0000"  >&lt;p&gt;diagnostic data in the primary server&lt;/p&gt;</comment>
                            <comment id="1608127" author="mark.agarunov" created="Tue, 27 Jun 2017 21:58:26 +0000"  >&lt;p&gt;Hello &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=John_Wang&quot; class=&quot;user-hover&quot; rel=&quot;John_Wang&quot;&gt;John_Wang&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;Thank you for the report. From your description of the issue, I believe this may be due to the &lt;tt&gt;vm.swapiness&lt;/tt&gt; value of the Linux kernel swapping out pages that haven&apos;t been recently accessed. However, to get a better idea of what may be causing this, please archive and upload the &lt;tt&gt;$dbPath/diagnostic.data&lt;/tt&gt; directory. This should give a bit more information as to what is causing this.&lt;/p&gt;

&lt;p&gt;Thanks,&lt;br/&gt;
Mark&lt;/p&gt;</comment>
                    </comments>
                    <attachments>
                            <attachment id="159618" name="diagnose_data.docx" size="23410" author="John_Wang" created="Tue, 27 Jun 2017 05:35:21 +0000"/>
                            <attachment id="159762" name="diagnostic.data.1.rar" size="110215666" author="John_Wang" created="Wed, 28 Jun 2017 03:03:44 +0000"/>
                            <attachment id="159763" name="diagnostic.data.2.rar" size="96589866" author="John_Wang" created="Wed, 28 Jun 2017 03:00:05 +0000"/>
                            <attachment id="159844" name="swap.png" size="64308" author="mark.agarunov" created="Wed, 28 Jun 2017 19:33:46 +0000"/>
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