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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-66098] Investigate read only mode for column indexes</title>
                <link>https://jira.mongodb.org/browse/SERVER-66098</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;There&apos;s a TODO that was left &lt;a href=&quot;https://github.com/10gen/mongo/blob/9a6e6077b9669523f54c512a0f64a275fbcae2af/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp#L1753&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;However, the flag seems to be ignored. This task is to see if there&apos;s any special behavior that standard indexes or collections do for read-only mode, and whether CSI has to mirror that behavior.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2036758">SERVER-66098</key>
            <summary>Investigate read only mode for column indexes</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="dianna.hohensee@mongodb.com">Dianna Hohensee</assignee>
                                    <reporter username="ian.boros@mongodb.com">Ian Boros</reporter>
                        <labels>
                            <label>pm2646-m4</label>
                    </labels>
                <created>Fri, 29 Apr 2022 22:56:51 +0000</created>
                <updated>Sun, 29 Oct 2023 21:38:45 +0000</updated>
                            <resolved>Wed, 7 Dec 2022 19:18:40 +0000</resolved>
                                                    <fixVersion>6.3.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="5038257" author="xgen-internal-githook" created="Wed, 7 Dec 2022 19:10:34 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Dianna Hohensee&apos;, &apos;email&apos;: &apos;dianna.hohensee@mongodb.com&apos;, &apos;username&apos;: &apos;DiannaHohensee&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66098&quot; title=&quot;Investigate read only mode for column indexes&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66098&quot;&gt;&lt;del&gt;SERVER-66098&lt;/del&gt;&lt;/a&gt; Remove readOnly from the WTColumnStore constructor: column store is an index and RecordStore writes already check for readOnly&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/402b2fac002941eeb67da425fc16264259226267&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/402b2fac002941eeb67da425fc16264259226267&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5030234" author="dianna.hohensee" created="Mon, 5 Dec 2022 16:37:37 +0000"  >&lt;p&gt;Ah, one thing maybe. &lt;a href=&quot;https://github.com/mongodb/mongo/blob/ddb2fefd9931ac72401209049b36d18c71e834d0/src/mongo/db/storage/record_store.cpp#L38-L42&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;RecordStore validates not readOnly mode&lt;/a&gt; for every &lt;a href=&quot;https://github.com/mongodb/mongo/blob/ddb2fefd9931ac72401209049b36d18c71e834d0/src/mongo/db/storage/record_store.cpp#L58&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;write&lt;/a&gt;. I suspect WTColumnStore is a variant of record store? (the class is undocumented). So maybe that should be added. Why doesn&apos;t WTColumnStore inherit from RecordStore?&lt;/p&gt;

&lt;p&gt;&lt;b&gt;UPDATE:&lt;/b&gt; &lt;/p&gt;

&lt;p&gt;Ah, WTColumnStore is more like a variant of SortedDataInterface (index equiv of RecordStore). Therefore, WTColumnStore need not do any checks because all writes will hit the RecordStore and then whatever indexes &amp;#8211; WTColumnStores and SortedDataInterfaces. So the RecordStore will always invariant and destroy the operation also trying to do index writes.&lt;/p&gt;</comment>
                            <comment id="5030214" author="dianna.hohensee" created="Mon, 5 Dec 2022 16:32:22 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=ian.boros%40mongodb.com&quot; class=&quot;user-hover&quot; rel=&quot;ian.boros@mongodb.com&quot;&gt;ian.boros@mongodb.com&lt;/a&gt; &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=steve.tarzia%40mongodb.com&quot; class=&quot;user-hover&quot; rel=&quot;steve.tarzia@mongodb.com&quot;&gt;steve.tarzia@mongodb.com&lt;/a&gt;&#160;Unless there&apos;s something particular either of you have in mind for column store regarding readOnly mode, I will go ahead and close this ticket.&lt;/p&gt;</comment>
                            <comment id="5030203" author="dianna.hohensee" created="Mon, 5 Dec 2022 16:31:26 +0000"  >&lt;p&gt;The WTColumnStore readOnly flag is &lt;a href=&quot;https://github.com/mongodb/mongo/blob/ddb2fefd9931ac72401209049b36d18c71e834d0/src/mongo/db/storage/wiredtiger/wiredtiger_column_store.cpp#L102&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;not used&lt;/a&gt;&#160;in the WTColumnStore constructor, which explains why it does not work.&lt;/p&gt;

&lt;p&gt;I don&apos;t believe that there is any work to be done in this ticket. The readOnly flag is actively used in the write path, and ensured for any write path via a combination of checks in the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/ddb2fefd9931ac72401209049b36d18c71e834d0/src/mongo/db/storage/write_unit_of_work.cpp#L59&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;WriteUnitOfWork&lt;/a&gt; and &lt;a href=&quot;https://github.com/mongodb/mongo/blob/ddb2fefd9931ac72401209049b36d18c71e834d0/src/mongo/db/storage/recovery_unit.h#L137-L138&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;RecoveryUnit&lt;/a&gt;. The readOnly flag is initialized via the &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/mongod_main.cpp#L440-L445&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;ServiceContext&lt;/a&gt; and &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/operation_context.h#L636-L647&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;OperationContext&lt;/a&gt;, and thus is present for every WUOW done on the server. There are means of bypassing the flag, by specially unsetting the opCtx I would expect, for special internal operations as they arise, but that is irrelevant to column store details.&lt;/p&gt;</comment>
                            <comment id="5024125" author="ian.boros" created="Fri, 2 Dec 2022 01:18:22 +0000"  >&lt;p&gt;Updated description.&lt;/p&gt;</comment>
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