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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>[DOCS-12863] Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present</title>
                <link>https://jira.mongodb.org/browse/DOCS-12863</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;

&lt;p&gt;SERVER ticket description: Currently the oplog cannot be dropped while running in replset mode, but can be dropped as standalone.  Until recently the procedure to resize the oplog included dropping the oplog while in standalone, however, doing this procedure on an uncleanly shutdown 4.0 mongod causes committed writes to be lost (because they only existed in the oplog, and the resize preserves only the final oplog entry, see &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12230&quot; title=&quot;Manual oplog resize in 4.0 after unclean shutdown can lose committed writes&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12230&quot;&gt;&lt;del&gt;DOCS-12230&lt;/del&gt;&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-38174&quot; title=&quot;Starting replica set member standalone can lose committed writes starting in MongoDB 4.0&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-38174&quot;&gt;&lt;del&gt;SERVER-38174&lt;/del&gt;&lt;/a&gt; for more details).  It would be much better if attempting this procedure in 4.0 did not result in oplog entries being lost, eg. if dropping the oplog failed.&lt;/p&gt;

&lt;p&gt;Completely forbidding oplog drop (even when standalone) would interfere with the use case of restoring a filesystem snapshot as a test standalone.  A better alternative would be to forbid dropping the oplog only if local.system.replset contains documents.  This way, users who are sure they want to drop the oplog can do so by first removing the documents from local.system.replset (which can&apos;t be dropped, but can have its contents removed) and then restarting the standalone.  Whereas users who are just trying to perform a manual oplog resize will be stopped before any data loss.&lt;/p&gt;

&lt;p&gt;If we choose not to do this, then at the very least we should improve the &quot;standalone-but-replset-config-exists&quot; startup warning to specifically warn against to manually resizing the oplog.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;ChangeDescription%3ATwothingsneedtobedocumented%3A&quot;&gt;&lt;/a&gt;Change Description: Two things need to be documented:&lt;/h2&gt;

&lt;p&gt;1)&lt;br/&gt;
The changes made in this ticket prevent the oplog from being dropped on a standalone node when the WiredTiger storage engine is being used (or any other storage engine that supports the replSetResizeOplog command; currently on the WiredTiger storage engine supports that command). Note that dropping the oplog is already forbidden for nodes running as a part of a replica set.&lt;br/&gt;
In the past, dropping the oplog was a step in the procedure to manually resize the oplog. However, dropping the oplog had a few bad side effects, and so we are trying to get users to use the replSetResizeOplog command.&lt;br/&gt;
(For further information please see Suganthi&apos;s comment on ticket &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-38356&quot; title=&quot;Forbid dropping oplog in standalone mode on storage engines that support replSetResizeOplog&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-38356&quot;&gt;&lt;del&gt;SERVER-38356&lt;/del&gt;&lt;/a&gt;)&lt;/p&gt;


&lt;p&gt;2)&lt;br/&gt;
Dropping the oplog can lead to data inconsistencies, as unapplied oplog entries can be lost. In her attempt to recreate this issue and see inconsistencies, Suganthi encountered a server crash instead due to an fassert: after an unclean shutdown on the MMAPv1 storage engine, on startup recovery the server tries to replay entries from the AppliedThroughTimestamp to the top of the oplog. It checks if the first timestamp it found matches the oplog application start point, and if not, crashes (&lt;a href=&quot;https://github.com/mongodb/mongo/blob/8f4b0b3817fbf48cc0025632802aec37d21946da/src/mongo/db/repl/replication_recovery.cpp#L134-L138&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/8f4b0b3817fbf48cc0025632802aec37d21946da/src/mongo/db/repl/replication_recovery.cpp#L134-L138&lt;/a&gt;).&lt;br/&gt;
More information can be found on Suganthi&apos;s comment on ticket &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-38356&quot; title=&quot;Forbid dropping oplog in standalone mode on storage engines that support replSetResizeOplog&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-38356&quot;&gt;&lt;del&gt;SERVER-38356&lt;/del&gt;&lt;/a&gt;.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="838475">DOCS-12863</key>
            <summary>Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present</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="jeffrey.allen@mongodb.com">Jeffrey Allen</assignee>
                                    <reporter username="backlog-server-pm">Backlog - Core Eng Program Management Team</reporter>
                        <labels>
                    </labels>
                <created>Mon, 8 Jul 2019 20:19:26 +0000</created>
                <updated>Mon, 13 Nov 2023 18:19:07 +0000</updated>
                            <resolved>Mon, 27 Jan 2020 15:56:16 +0000</resolved>
                                                    <fixVersion>4.3.1</fixVersion>
                    <fixVersion>4.2.1</fixVersion>
                    <fixVersion>Server_Docs_20231030</fixVersion>
                    <fixVersion>Server_Docs_20231106</fixVersion>
                    <fixVersion>Server_Docs_20231105</fixVersion>
                    <fixVersion>Server_Docs_20231113</fixVersion>
                                    <component>manual</component>
                    <component>Server</component>
                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="2867602" author="xgen-internal-githook" created="Tue, 11 Feb 2020 22:40:40 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;jeff-allen-mongo&apos;, &apos;name&apos;: &apos;jeff-allen-mongo&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12863&quot; title=&quot;Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12863&quot;&gt;&lt;del&gt;DOCS-12863&lt;/del&gt;&lt;/a&gt;): Forbid dropping oplog in all scenarios&lt;br/&gt;
Branch: v4.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/ce5192dc3dfe9122490776f9a21680f163c4cbfe&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/ce5192dc3dfe9122490776f9a21680f163c4cbfe&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2765735" author="xgen-internal-githook" created="Mon, 27 Jan 2020 15:56:33 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;, &apos;name&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12863&quot; title=&quot;Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12863&quot;&gt;&lt;del&gt;DOCS-12863&lt;/del&gt;&lt;/a&gt;): Forbid dropping oplog in all scenarios&lt;br/&gt;
Branch: v4.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/40ebab40b67ffb4258d17a160ad64194a080fb8e&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/40ebab40b67ffb4258d17a160ad64194a080fb8e&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2765730" author="xgen-internal-githook" created="Mon, 27 Jan 2020 15:55:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;jeff-allen-mongo&apos;, &apos;name&apos;: &apos;jeff-allen-mongo&apos;, &apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12863&quot; title=&quot;Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12863&quot;&gt;&lt;del&gt;DOCS-12863&lt;/del&gt;&lt;/a&gt;): Forbid dropping oplog in all scenarios&lt;br/&gt;
Branch: v4.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/ce5192dc3dfe9122490776f9a21680f163c4cbfe&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/ce5192dc3dfe9122490776f9a21680f163c4cbfe&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2765728" author="xgen-internal-githook" created="Mon, 27 Jan 2020 15:54:20 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;jeffrey.allen@10gen.com&apos;, &apos;username&apos;: &apos;jeff-allen-mongo&apos;, &apos;name&apos;: &apos;jeff-allen-mongo&apos;}
&lt;p&gt;Message: (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-12863&quot; title=&quot;Investigate changes in SERVER-38356: Forbid dropping oplog when replset config is present&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-12863&quot;&gt;&lt;del&gt;DOCS-12863&lt;/del&gt;&lt;/a&gt;): Forbid dropping oplog in all scenarios&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/482ea749dfa5a5a7119b18a6d9e6f25a846d971c&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/482ea749dfa5a5a7119b18a6d9e6f25a846d971c&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
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                                        <issuelink>
            <issuekey id="641799">SERVER-38356</issuekey>
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                    <name>Related</name>
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            <issuekey id="1316227">DOCS-13596</issuekey>
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