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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-33846] Alternative for setting oplog read timestamp on secondaries</title>
                <link>https://jira.mongodb.org/browse/SERVER-33846</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Currently, the oplog read timestamp is set via the same asynchronous mechanism, regardless of replication state (PRIMARY or SECONDARY): a thread loop takes note of the latest oplog entry&apos;s optime with no holes after it, waits for journal, and then publishes that optime as the new oplog read value.&lt;br/&gt;
The algorithm is correct for primary nodes.  However, as an optimization, it does not have to wait for journaling on secondary nodes, because it is never possible to read holes after an unclean shutdown of a secondary node (due to our durable storing of the last applied time).  Today, we have a problem with the stable timestamp (and oldest timestamp) racing ahead of the oplog read timestamp on secondaries.  By forgoing the wait for journaling on secondaries, we can set the oplog read timestamp in lock step with the stable timestamp and oldest timestamp, thus avoiding the race.&lt;/p&gt;

&lt;p&gt;The work for this ticket will be to change the oplog read timestamp loop to only operate while a node is in primary mode; in secondary mode, new code inserted into the applier loop will set the oplog read timestamp when the last applied time is set.&lt;/p&gt;</description>
                <environment></environment>
        <key id="510422">SERVER-33846</key>
            <summary>Alternative for setting oplog read timestamp on secondaries</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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="13201">Fixed</resolution>
                                        <assignee username="daniel.gottlieb@mongodb.com">Daniel Gottlieb</assignee>
                                    <reporter username="milkie@mongodb.com">Eric Milkie</reporter>
                        <labels>
                            <label>rollback-functional</label>
                    </labels>
                <created>Tue, 13 Mar 2018 13:54:01 +0000</created>
                <updated>Sun, 29 Oct 2023 22:33:50 +0000</updated>
                            <resolved>Fri, 16 Mar 2018 01:42:01 +0000</resolved>
                                                    <fixVersion>3.7.4</fixVersion>
                                    <component>Replication</component>
                    <component>Storage</component>
                                        <votes>1</votes>
                                    <watches>6</watches>
                                                                                                                <comments>
                            <comment id="1835979" author="xgen-internal-githook" created="Fri, 16 Mar 2018 01:41:50 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;daniel.gottlieb@mongodb.com&apos;, &apos;name&apos;: &apos;Daniel Gottlieb&apos;, &apos;username&apos;: &apos;dgottlieb&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-33846&quot; title=&quot;Alternative for setting oplog read timestamp on secondaries&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-33846&quot;&gt;&lt;del&gt;SERVER-33846&lt;/del&gt;&lt;/a&gt;: Set oplog visibility synchronously on secondaries, at the end of every batch.&lt;/p&gt;

&lt;p&gt;This patch introduces an optimization to allow secondaries to set their&lt;br/&gt;
visibility synchronously with oplog application as well as bypassing&lt;br/&gt;
additional journal flushing meant for primaries. Primaries replicating oplog&lt;br/&gt;
entries atomically generate a new optime and pass it to the storage engine&apos;s&lt;br/&gt;
oplog record store via the `oplogDiskLocRegister` method. This code path&lt;br/&gt;
will now pass in a parameter `orderedCommit = false` that alerts the storage&lt;br/&gt;
engine to maintain the necessary oplog visibility semantics for that write.&lt;br/&gt;
This is existing behavior, the only difference is the addition of the&lt;br/&gt;
`orderedCommit` parameter.&lt;/p&gt;

&lt;p&gt;Secondaries will now also call `oplogDiskLocRegister` at the end of every&lt;br/&gt;
batch. This call will pass in the optime of the last oplog entry applied and&lt;br/&gt;
`orderedCommit = true`. A storage engine may take this as a guarantee that&lt;br/&gt;
there are no oplog holes prior to the input optime.&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/8ab8025f23fb50d15336870a6cea4e4ca6f9673a&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/8ab8025f23fb50d15336870a6cea4e4ca6f9673a&lt;/a&gt;&lt;/p&gt;</comment>
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            <issuekey id="775236">SERVER-41291</issuekey>
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                                        <issuelink>
            <issuekey id="684317">SERVER-39383</issuekey>
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