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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-55035] Mongo Write Lock shows 100 %, even there are no write operations shown in mongostat output</title>
                <link>https://jira.mongodb.org/browse/SERVER-55035</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;&lt;em&gt;mongostats&lt;/em&gt; shows &lt;b&gt;100 %&lt;/b&gt; write lock during some specific period. However, during the same period &lt;em&gt;mongotop&lt;/em&gt; shows &lt;b&gt;zero&lt;/b&gt; write operations on a mongo cluster.&#160;&lt;/p&gt;

&lt;p&gt;Could you please clarify how mongostat shows 100 % write lock (lrw column) when there is no write operations seen in mongotop output !&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;System Configuration&lt;/p&gt;

&lt;p&gt;Os Version: CentOS 7&lt;br/&gt;
cat /etc/redhat-release&lt;br/&gt;
CentOS Linux release 7.6.1810 (Core)&lt;br/&gt;
Mongo Version : 3.4.16&lt;br/&gt;
Storage Engine: mmapV1&lt;br/&gt;
Storage Type: Data Path in tmpfs&lt;/p&gt;

&lt;p&gt;&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: run: df -hP -x iso9660&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: Filesystem Size Used Avail Use% Mounted on&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: /dev/sda2 95G 19G 71G 22% /&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: devtmpfs 50G 0 50G 0% /dev&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: tmpfs 50G 28K 50G 1% /dev/shm&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: tmpfs 50G 2.1G 48G 5% /run&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: tmpfs 50G 0 50G 0% /sys/fs/cgroup&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: tmpfs 59G 0 59G 0% /var/data/sessions.1&lt;br/&gt;
&lt;span class=&quot;error&quot;&gt;&amp;#91;sessionmgr05&amp;#93;&lt;/span&gt; out: tmpfs 9.9G 0 9.9G 0% /run/user/0&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;Attached mongotop, mongostat outputs&#160; for 100 % write lock periods.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="1643317">SERVER-55035</key>
            <summary>Mongo Write Lock shows 100 %, even there are no write operations shown in mongostat output</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-triage">Backlog - Triage Team</assignee>
                                    <reporter username="kokilasoumi@gmail.com">Kokila Soumi</reporter>
                        <labels>
                    </labels>
                <created>Mon, 8 Mar 2021 15:32:40 +0000</created>
                <updated>Tue, 6 Dec 2022 01:32:10 +0000</updated>
                            <resolved>Tue, 9 Mar 2021 08:12:19 +0000</resolved>
                                                                    <component>Tools</component>
                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="3689425" author="JIRAUSER1269890" created="Mon, 29 Mar 2021 17:47:14 +0000"  >&lt;p&gt;Hi Dmitry -&#160;&lt;/p&gt;

&lt;p&gt;yes , We have upgraded the mongo to a later in the latest version of the product. However , the product in the field is running mongo db 3.4.&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;Kokila&apos;s question was , &quot;lrw&quot; column in mongostat output shows which lock %. In the use case mentioned , write lock goes to 100% , eventhough no write operations are taking place.As I understand there are various locks for various entities ( refer the link here&#160; &lt;a href=&quot;https://docs.mongodb.com/v3.6/reference/method/db.currentOp/#db.currentOp]&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;[db.currentOp() &#8212; MongoDB Manual&lt;/a&gt;&#160;.&lt;/p&gt;

&lt;p&gt; Is monitoring lrw&#160; lock % recommended practice to know the health of the mongod instance. ( apart from the CPU &amp;amp; mem utilization ) . &lt;/p&gt;

&lt;p&gt;Can you suggest monitoring any other parameter and be assured mongod instance is hale and healthy ?&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;Can you please share your comments. Your response is much appreciated !&lt;/p&gt;</comment>
                            <comment id="3653832" author="dmitry.agranat" created="Tue, 9 Mar 2021 08:12:06 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=kokilasoumi%40gmail.com&quot; class=&quot;user-hover&quot; rel=&quot;kokilasoumi@gmail.com&quot;&gt;kokilasoumi@gmail.com&lt;/a&gt;, MongoDB 3.4 &lt;a href=&quot;https://www.mongodb.com/support-policy&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;reached end of life in January of 2020&lt;/a&gt;. For general questions like this, we&apos;d like to encourage you to start by asking our community for help by posting on the &lt;a href=&quot;https://community.mongodb.com&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;MongoDB Developer Community Forums&lt;/a&gt;.&lt;/p&gt;</comment>
                    </comments>
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                            <attachment id="303755" name="Write_lock_Graph.png" size="89185" author="kokilasoumi@gmail.com" created="Mon, 8 Mar 2021 15:28:47 +0000"/>
                            <attachment id="303757" name="mongostat.png" size="70787" author="kokilasoumi@gmail.com" created="Mon, 8 Mar 2021 15:28:47 +0000"/>
                            <attachment id="303756" name="mongotop.pdf" size="266466" author="kokilasoumi@gmail.com" created="Mon, 8 Mar 2021 15:28:48 +0000"/>
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