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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-55821] remove next_random_sample_size=1000 configuration in the oplog sampling code</title>
                <link>https://jira.mongodb.org/browse/SERVER-55821</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The use of the next_random_sample_size option when creating random cursors on a WiredTiger record store is not applicable anymore due to unbalanced trees being a non-issue in recent MongoDB releases and customer deployments. The work for this ticket involves removing the use of this option from the oplog sampling code in wiredtiger_record_store.cpp for 5.1 and to evaluate removing the support for this option in the WiredTiger storage engine at a later time.&lt;/p&gt;

&lt;p&gt;PREVIOUS SUMMARY: Investigate slow random cursor operations on oplog&lt;/p&gt;

&lt;p&gt;Random cursors can be quite slow on a multi-GB oplog table.&lt;/p&gt;

&lt;p&gt;A customer has experienced slow startup times in 4.2 that they didn&apos;t see in 4.0. &#160;Based on their logs mongod is spending a lot of time iterating a random cursor though the oplog &#8212; in one case it takes 15 minutes to perform 993&#160;&lt;tt&gt;cursor-&amp;gt;next()&lt;/tt&gt;&#160;calls on a ~26GB oplog. &#160;The oplog had only 62590 records, so the average record size is 100s of KB.&lt;/p&gt;


&lt;p&gt;See &lt;a href=&quot;https://jira.mongodb.org/browse/WT-7373&quot; title=&quot;Improve slow random cursor operations on oplog&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-7373&quot;&gt;&lt;del&gt;WT-7373&lt;/del&gt;&lt;/a&gt; for more discussion.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1672008">SERVER-55821</key>
            <summary>remove next_random_sample_size=1000 configuration in the oplog sampling code</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="13201">Fixed</resolution>
                                        <assignee username="benety.goh@mongodb.com">Benety Goh</assignee>
                                    <reporter username="keith.bostic@mongodb.com">Keith Bostic</reporter>
                        <labels>
                    </labels>
                <created>Tue, 6 Apr 2021 17:41:50 +0000</created>
                <updated>Sun, 29 Oct 2023 21:55:17 +0000</updated>
                            <resolved>Tue, 6 Jul 2021 15:31:56 +0000</resolved>
                                                    <fixVersion>5.1.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>9</watches>
                                                                                                                <comments>
                            <comment id="4108353" author="JIRAUSER1259052" created="Wed, 6 Oct 2021 19:04:40 +0000"  >&lt;p&gt;Updating the fixversion since branching activities occurred yesterday. This ticket will be in rc0 when it&#8217;s been triggered. For more active release information, please keep an eye on #server-release. Thank you!&lt;/p&gt;</comment>
                            <comment id="3916501" author="xgen-internal-githook" created="Mon, 5 Jul 2021 12:32:42 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Benety Goh&apos;, &apos;email&apos;: &apos;benety@mongodb.com&apos;, &apos;username&apos;: &apos;benety&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-55821&quot; title=&quot;remove next_random_sample_size=1000 configuration in the oplog sampling code&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-55821&quot;&gt;&lt;del&gt;SERVER-55821&lt;/del&gt;&lt;/a&gt; remove WiredTigerRecordStore::getRandomCursorWithOptions()&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/2fa358f0a35618daeded2686ef25e032f94c75cc&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/2fa358f0a35618daeded2686ef25e032f94c75cc&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3915966" author="xgen-internal-githook" created="Sun, 4 Jul 2021 12:23:30 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Benety Goh&apos;, &apos;email&apos;: &apos;benety@mongodb.com&apos;, &apos;username&apos;: &apos;benety&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-55821&quot; title=&quot;remove next_random_sample_size=1000 configuration in the oplog sampling code&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-55821&quot;&gt;&lt;del&gt;SERVER-55821&lt;/del&gt;&lt;/a&gt; remove next_random_sample_size=1000 configuration in the oplog sampling code&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/671f32cfb27e08301e6564224338f6d035337e74&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/671f32cfb27e08301e6564224338f6d035337e74&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3915889" author="xgen-internal-githook" created="Sat, 3 Jul 2021 19:13:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Benety Goh&apos;, &apos;email&apos;: &apos;benety@mongodb.com&apos;, &apos;username&apos;: &apos;benety&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-55821&quot; title=&quot;remove next_random_sample_size=1000 configuration in the oplog sampling code&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-55821&quot;&gt;&lt;del&gt;SERVER-55821&lt;/del&gt;&lt;/a&gt; log minBytesPerStone when sampling oplog for placing stones&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/6ff9a52b5ab0bcc44eecd1dacf19d0b6bc30361e&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/6ff9a52b5ab0bcc44eecd1dacf19d0b6bc30361e&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3908279" author="benety.goh" created="Tue, 29 Jun 2021 17:59:18 +0000"  >&lt;p&gt;We started &lt;a href=&quot;https://github.com/mongodb/mongo/commit/294a8f68615710b47936d5ee42439d01538ac746#diff-8215f5586c669f98915b0db79a93f6088a5d2dffdce3bec5d3c6c6371d3593a5R327&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;logging the WiredTiger oplog processing time&lt;/a&gt;&#160;in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-43322&quot; title=&quot;Add tracking tools for measuring OplogStones performance&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-43322&quot;&gt;&lt;del&gt;SERVER-43322&lt;/del&gt;&lt;/a&gt;. These stats are also available in db.serverStatus() under the &lt;a href=&quot;https://docs.mongodb.com/manual/reference/command/serverStatus/#oplogtruncation&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;oplogTruncation section&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="3900431" author="benety.goh" created="Fri, 25 Jun 2021 14:27:15 +0000"  >&lt;p&gt;(Reproducing some of the context from &lt;a href=&quot;https://jira.mongodb.org/browse/WT-7373&quot; title=&quot;Improve slow random cursor operations on oplog&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-7373&quot;&gt;&lt;del&gt;WT-7373&lt;/del&gt;&lt;/a&gt;) The &lt;a href=&quot;https://github.com/mongodb/mongo/commit/4463e0366bac5874e4c527b88f25045d544850a5#diff-8215f5586c669f98915b0db79a93f6088a5d2dffdce3bec5d3c6c6371d3593a5R388&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;next_random_sample_size&lt;/a&gt; option was added in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-21920&quot; title=&quot;Use enhanced WiredTiger next_random cursors for oplog stones&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-21920&quot;&gt;&lt;del&gt;SERVER-21920&lt;/del&gt;&lt;/a&gt;.&lt;/p&gt;</comment>
                            <comment id="3703662" author="keith.bostic" created="Tue, 6 Apr 2021 17:44:41 +0000"  >&lt;p&gt;This ticket is a place to investigate and potentially make changes to remove the &lt;tt&gt;next_random_sample_size=1000&lt;/tt&gt; configuration in the MongoDB server oplog sampling code, see &lt;a href=&quot;https://jira.mongodb.org/browse/WT-7373&quot; title=&quot;Improve slow random cursor operations on oplog&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-7373&quot;&gt;&lt;del&gt;WT-7373&lt;/del&gt;&lt;/a&gt; for the discussion.&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=geert.bosch&quot; class=&quot;user-hover&quot; rel=&quot;geert.bosch&quot;&gt;geert.bosch&lt;/a&gt;, I apologize for assigning this to you, but I wasn&apos;t sure of the right path and you&apos;ve been flagged on some of the discussions, please don&apos;t hesitate to move this as you see fit.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="1659930">WT-7373</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="926202">SERVER-43322</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="222381">SERVER-19551</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="244125">SERVER-21920</issuekey>
        </issuelink>
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