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    <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-10780] Clock skew and balancing in MONGOS</title>
                <link>https://jira.mongodb.org/browse/SERVER-10780</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;We have around 3 app servers on which we are running mongos which connect to 3 config servers.&lt;/p&gt;

&lt;p&gt;There was following error in one of the mongos server logs:&lt;/p&gt;

&lt;p&gt;1) &quot;&quot;&lt;span class=&quot;error&quot;&gt;&amp;#91;Balancer&amp;#93;&lt;/span&gt; caught exception while doing balance: error checking clock skew of cluster CFG1.hma.com:30000, CFG2.hma.com:30000,CFG3.hma.com:30000 :: caused by :: 13650 clock skew of the cluster CFG1.hma.com:30000, CFG2.hma.com:30000, CFG3.hma.com:30000 is too far out of bounds to allow distributed locking.&quot;&quot;&lt;/p&gt;


&lt;p&gt;This is due to time difference but we have ntpd service running. The difference between time of One working Mongos Server to Non-Working mOngos is around 10sec which i don&apos;t think should create this issue.&lt;/p&gt;

&lt;p&gt;2)Mon Sep 16 08:07:47.049 &lt;span class=&quot;error&quot;&gt;&amp;#91;Balancer&amp;#93;&lt;/span&gt; distributed lock &apos;balancer/WEB002:27017:1374748868:1804289383&apos; unlocked. &lt;br/&gt;
Mon Sep 16 08:07:53.267 &lt;span class=&quot;error&quot;&gt;&amp;#91;Balancer&amp;#93;&lt;/span&gt; distributed lock &apos;balancer/WEB002:27017:1374748868:1804289383&apos; acquired, ts : 5236f4998003d9842486ab03&lt;br/&gt;
Mon Sep 16 08:07:53.372 &lt;span class=&quot;error&quot;&gt;&amp;#91;Balancer&amp;#93;&lt;/span&gt; distributed lock &apos;balancer/WEB002:27017:1374748868:1804289383&apos; unlocked. &quot;&lt;/p&gt;

&lt;p&gt;This is coming on one of the mongos server. - Wanted to confirm is balancing works only on one of the mongos server.&lt;/p&gt;

&lt;p&gt;Also,  db.locks.find( &lt;/p&gt;
{ _id : &quot;balancer&quot; }
&lt;p&gt; ).pretty() gave following output:-&lt;br/&gt;
{&lt;br/&gt;
	&quot;_id&quot; : &quot;balancer&quot;,&lt;br/&gt;
	&quot;process&quot; : &quot;WEB001:27017:1374748869:1804289383&quot;,&lt;br/&gt;
	&quot;state&quot; : 0,&lt;br/&gt;
	&quot;ts&quot; : ObjectId(&quot;5236f315abd060ee92056a41&quot;),&lt;br/&gt;
	&quot;when&quot; : ISODate(&quot;2013-09-16T12:01:25.938Z&quot;),&lt;br/&gt;
	&quot;who&quot; : &quot;T00AWSPWEB001.HMA.COM:27000:1374748869:1804289383:Balancer:846930886&quot;,&lt;br/&gt;
	&quot;why&quot; : &quot;doing balance round&quot;&lt;br/&gt;
}&lt;/p&gt;


&lt;p&gt;So to summaries all 3 mongos(A, B, C) show different status: In A no log is generated(working fine), In B clock skew issue is coming(not working correctly), In C distributed lock issue is coming.&lt;/p&gt;
</description>
                <environment></environment>
        <key id="90016">SERVER-10780</key>
            <summary>Clock skew and balancing in MONGOS</summary>
                <type id="6" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Question</type>
                                            <priority id="1" iconUrl="https://jira.mongodb.org/images/icons/priorities/blocker.svg">Blocker - P1</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="-1">Unassigned</assignee>
                                    <reporter username="somit">Somit Srivastava</reporter>
                        <labels>
                    </labels>
                <created>Mon, 16 Sep 2013 12:20:25 +0000</created>
                <updated>Wed, 10 Dec 2014 23:18:01 +0000</updated>
                            <resolved>Tue, 18 Mar 2014 12:58:38 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="518262" author="stennie" created="Tue, 18 Mar 2014 12:58:38 +0000"  >&lt;p&gt;Hi Somit,&lt;/p&gt;

&lt;p&gt;Please be advised I&apos;m closing this issue due to inactivity.&lt;/p&gt;

&lt;p&gt;Large amounts of clock skew can cause unexpected issues for many programs, particularly if adjustments cause servers to skip back in time. MongoDB has some tolerance for clock skew, but as per the log message you encountered there are sanity checks to keep the skew within reason.&lt;/p&gt;

&lt;p&gt;If you do encounter a warning on clock skew, the appropriate fix would be to synchronise the server times and ensure ntpd is working correctly.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Stephen&lt;/p&gt;</comment>
                            <comment id="463486" author="eliot" created="Sat, 30 Nov 2013 05:17:37 +0000"  >&lt;p&gt;Is this still an issue?&lt;br/&gt;
Can you send times on all servers and mongodump of config server if so.&lt;/p&gt;</comment>
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