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    <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-8475] Small clock skew with NTP can give strange locked values on queries</title>
                <link>https://jira.mongodb.org/browse/SERVER-8475</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p/&gt;
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&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;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 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;Tue Feb  5 04:24:26 [conn12345] command XXXXX.$cmd command: { findandmodify: &quot;XXXXX&quot;, query: { _id: 123456 }, sort: { _id: 1 }, new: 1, remove: 0, upsert: 0, update: { $pull: { XXXXX: &quot;GUID&quot; } } } ntoreturn:1 keyUpdates:0 locks(micros) w:18446743918042 reslen:336 1271310163ms&lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;

&lt;p&gt;The write lock value on that query appears to be 7 months. &lt;/p&gt;

&lt;p&gt;Checking their NTPD logs showed that ntpd was winding back 140 milliseconds (by default its max ntp will do is 200ms)&lt;/p&gt;

&lt;p&gt;This looks like it could cause problems in our query execution - as it becomes possible for a query to appear to have started after it ended.&lt;/p&gt;

&lt;p&gt;Checking the Timer (util/timer.h) class shows that if we have a clock windback around when we call now() we could potentially generate a negative number. The values we use to capture these numbers are &lt;tt&gt;unsigned long long&lt;/tt&gt;&apos;s which would cause problems in the event of a negative number.&lt;/p&gt;
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                <environment></environment>
        <key id="64588">SERVER-8475</key>
            <summary>Small clock skew with NTP can give strange locked values on queries</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="3">Duplicate</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="david.hows">David Hows</reporter>
                        <labels>
                    </labels>
                <created>Fri, 8 Feb 2013 02:42:33 +0000</created>
                <updated>Fri, 25 Oct 2013 14:02:51 +0000</updated>
                            <resolved>Fri, 25 Oct 2013 14:02:51 +0000</resolved>
                                                                    <component>Diagnostics</component>
                                        <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="446651" author="eliot" created="Fri, 25 Oct 2013 14:02:51 +0000"  >&lt;p&gt;Yup, thanks, dup of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4740&quot; title=&quot;Use monotonic clock sources for Timer&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4740&quot;&gt;&lt;del&gt;SERVER-4740&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="446080" author="asya" created="Thu, 24 Oct 2013 15:34:17 +0000"  >&lt;p&gt;dup of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4740&quot; title=&quot;Use monotonic clock sources for Timer&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4740&quot;&gt;&lt;del&gt;SERVER-4740&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
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