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        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[COMPASS-6094] Investigate changes in SERVER-68783: Recipient shard may incorrectly return 0 milliseconds remaining in resharding</title>
                <link>https://jira.mongodb.org/browse/COMPASS-6094</link>
                <project id="13182" key="COMPASS">Compass </project>
                    <description>    &lt;div class=&quot;panel&quot; style=&quot;background-color: #c2d2c2;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;background-color: #239eb0;&quot;&gt;&lt;b&gt;Original Downstream Change Summary&lt;/b&gt;&lt;/div&gt;&lt;/div&gt;
&lt;p&gt;    Previously, a resharding operation would report that its estimated time remaining is 0 if either 1. the operation is very close to finishing or 2. an estimate could not be computed. Now, a value of 0 will only be reported in the former case. The visible effects of this change are as follows:&lt;/p&gt;

&lt;p&gt;1. In the $currentOp output for a resharding operation, the remainingOperationTimeEstimatedSecs field may not be present if an estimate could not be computed. Previously, this field would always be present, and have a value of 0 if the estimate could not be computed.&lt;/p&gt;

&lt;p&gt;2. In the serverStatus output, the shardingStatistics.resharding.coordinatorAllShardsLowestRemainingOperationTimeEstimatedMillis, shardingStatistics.resharding.coordinatorAllShardsHighestRemainingOperationTimeEstimatedMillis, and shardingStatistics.resharding.recipientRemainingOperationTimeEstimatedMillis fields will report a value of -1 if an estimate could not be computed. Previously, these fields would report a value of 0 in this case.&lt;/p&gt;
&lt;h2&gt;&lt;a name=&quot;DescriptionofLinkedTicket&quot;&gt;&lt;/a&gt;Description of Linked Ticket&lt;/h2&gt;
&lt;p&gt;    In response to a _shardsvrReshardingOperationTime command (used for querying the estimated remaining time in a resharding operation) from the resharding coordinator, a recipient shard executes &lt;a href=&quot;https://github.com/10gen/mongo/blob/01eb71c/src/mongo/db/s/shardsvr_resharding_operation_time_command.cpp#L120&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;this&lt;/a&gt; code, which calls &lt;a href=&quot;https://github.com/10gen/mongo/blob/master/src/mongo/db/s/resharding/resharding_metrics.cpp#L136&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;ReshardingMetrics::getRecipientHighEstimateRemainingTimeMillis&lt;/a&gt; to compute the estimate of the remaining time.&#160; That function may return 0 incorrectly if the shard has just had a failover, and not yet restored all of the metrics.&#160; &#160;That can happen because the metrics are only partly restored &lt;a href=&quot;https://github.com/10gen/mongo/blob/eda2f5d/src/mongo/db/s/resharding/resharding_recipient_service.cpp#L196&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt; and partly restored &lt;a href=&quot;https://github.com/10gen/mongo/blob/eda2f5d/src/mongo/db/s/resharding/resharding_recipient_service.cpp#L1236&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here.&lt;/a&gt;&lt;/p&gt;

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

&lt;p&gt;As a result, if a _shardsvrReshardingOperationTime command enters the system at the wrong time, it may observe only partly restored metrics, and the coordinator would be misled into believing that it can begin the critical section.&lt;/p&gt;

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

&lt;p&gt;This is related to &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-67653&quot; title=&quot;Resharding coordinator can incorrectly conclude that it can start the critical section although on one recipient the oplog applier hasn&amp;#39;t caught up with the oplog fetcher&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-67653&quot;&gt;&lt;del&gt;SERVER-67653&lt;/del&gt;&lt;/a&gt;, but is not the same because in that ticket the coordinator incorrectly treats an omitted remainingMillis field as 0 remainingMillis.&#160; In this ticket, the recipient incorrectly returns 0 remainingMillis.&lt;/p&gt;
</description>
                <environment></environment>
        <key id="2127745">COMPASS-6094</key>
            <summary>Investigate changes in SERVER-68783: Recipient shard may incorrectly return 0 milliseconds remaining in resharding</summary>
                <type id="10501" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Investigation</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="-1">Unassigned</assignee>
                                    <reporter username="backlog-server-pm">Backlog - Core Eng Program Management Team</reporter>
                        <labels>
                    </labels>
                <created>Thu, 1 Sep 2022 17:52:34 +0000</created>
                <updated>Fri, 2 Sep 2022 10:22:00 +0000</updated>
                            <resolved>Fri, 2 Sep 2022 10:22:00 +0000</resolved>
                                                    <fixVersion>No version</fixVersion>
                                        <due></due>
                            <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="4797489" author="JIRAUSER1256529" created="Fri, 2 Sep 2022 10:22:00 +0000"  >&lt;p&gt;No impact.&lt;/p&gt;</comment>
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