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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>
    </build-info>


<item>
            <title>[SERVER-73550] Segmentation fault: in mongo::ephemeral_for_test::RadixStore::_mergeResolveConflict</title>
                <link>https://jira.mongodb.org/browse/SERVER-73550</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I&apos;m working on a JS progam using MongoDB. Our integration tests use the npm library `mongo-memory-server` to download/run a mongod server with ephemeral_for_tests engine.&lt;/p&gt;

&lt;p&gt;Each test cleans its test collections by issuing `collection.deleteMany({})` on every modified collection during the test. All these deleteMany are executed in parallel.&lt;/p&gt;

&lt;p&gt;When executing many tests, it happens that the mongod server crashes with a segfault.&lt;/p&gt;

&lt;p&gt;&lt;ins&gt;Workarounds&lt;/ins&gt;&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;If I switch the deletions to be executed 1 by 1 (no parallelism), the crash doesn&apos;t occur anymore.&lt;/li&gt;
	&lt;li&gt;The crash occurs with mongod 5.0.14 and 6.0.4. If I downgrade to 4.4.18, the crash doesn&apos;t occur anymore.&#160;&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;----------------&lt;/p&gt;

&lt;p&gt;I was able to generate 2 core dumps (in attachment) with mongod 6.0.4:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;One sees the segfault in ephemeral_for_test::RadixStore&amp;lt;...&amp;gt;::merge3&lt;/li&gt;
	&lt;li&gt;The other in&#160; mongo::ephemeral_for_test::CursorBase::setEndPosition&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="2250941">SERVER-73550</key>
            <summary>Segmentation fault: in mongo::ephemeral_for_test::RadixStore::_mergeResolveConflict</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="2">Won&apos;t Fix</resolution>
                                        <assignee username="louis.williams@mongodb.com">Louis Williams</assignee>
                                    <reporter username="luc.vidal@360learning.com">Luc Vidal</reporter>
                        <labels>
                    </labels>
                <created>Thu, 2 Feb 2023 15:48:48 +0000</created>
                <updated>Mon, 27 Feb 2023 09:15:35 +0000</updated>
                            <resolved>Wed, 8 Feb 2023 09:11:57 +0000</resolved>
                                    <version>5.0.14</version>
                    <version>6.0.4</version>
                                                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="5177626" author="louis.williams" created="Wed, 8 Feb 2023 09:11:37 +0000"  >&lt;p&gt;Thanks &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=luc.vidal%40360learning.com&quot; class=&quot;user-hover&quot; rel=&quot;luc.vidal@360learning.com&quot;&gt;luc.vidal@360learning.com&lt;/a&gt;. I agree it would be a good idea to warn them about the breaking change coming in 7.0. I also filed a ticket (&lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-15887&quot; title=&quot;Investigate changes in SERVER-65151: Remove ephemeralForTest&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-15887&quot;&gt;&lt;del&gt;DOCS-15887&lt;/del&gt;&lt;/a&gt;) to make sure we update our documentation.&lt;/p&gt;</comment>
                            <comment id="5177521" author="JIRAUSER1272734" created="Wed, 8 Feb 2023 08:33:23 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=louis.williams%40mongodb.com&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;Louis Williams&lt;/a&gt;, thank you so much for your detailed explanation.&lt;/p&gt;

&lt;p&gt;I&apos;ll ping the owner of npm library `mongo-memory-server` to warn them about this.&lt;/p&gt;

&lt;p&gt;From my point of view, you can close this issue.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</comment>
                            <comment id="5175779" author="louis.williams" created="Tue, 7 Feb 2023 20:12:15 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=luc.vidal%40360learning.com&quot; class=&quot;user-hover&quot; rel=&quot;luc.vidal@360learning.com&quot;&gt;luc.vidal@360learning.com&lt;/a&gt;, I just want to elaborate on &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=yuan.fang%40mongodb.com&quot; class=&quot;user-hover&quot; rel=&quot;yuan.fang@mongodb.com&quot;&gt;yuan.fang@mongodb.com&lt;/a&gt;&apos;s comment above:&lt;/p&gt;

&lt;p&gt;In 5.0, we replaced the ephemeralForTest storage engine implementation with a different one, codenamed &quot;Biggie&quot; internally. But it&apos;s still called ephemeralForTest for your purposes. The new implementation was much more sophisticated, but it proved very difficult to maintain. It had many bugs, like the one you discovered, and in the 7.0 release, we will remove the ephemeralForTest engine entirely (see &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-65151&quot; title=&quot;Remove ephemeralForTest&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-65151&quot;&gt;&lt;del&gt;SERVER-65151&lt;/del&gt;&lt;/a&gt;).&lt;/p&gt;

&lt;p&gt;What does that mean for you? Luckily, the default WiredTiger storage engine is very fast, and it also happens to have strong durability guarantees. So long as you&apos;re not constantly starting and stopping the database, WiredTiger should be a suitable alternative for your purposes. You can also mount the database to a tmpfs (Temporary File System), and startup/shutdown should be even faster. Let me know if this provides a suitable workaround.&lt;/p&gt;</comment>
                            <comment id="5174967" author="JIRAUSER1270794" created="Tue, 7 Feb 2023 17:20:51 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=luc.vidal%40360learning.com&quot; class=&quot;user-hover&quot; rel=&quot;luc.vidal@360learning.com&quot;&gt;luc.vidal@360learning.com&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;Thank you for contacting us. Unfortunately, the support for the ephemeralForTest feature has reached its end of life in MongoDB. For this issue, we&apos;d like to encourage you to start by asking our community for help by posting on the &lt;a href=&quot;https://www.mongodb.com/community/forums&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;MongoDB Developer Community Forums&lt;/a&gt;. If the discussion there leads you to suspect a bug in the MongoDB server, then we&apos;d want to investigate it as a possible bug here in the SERVER project.&lt;/p&gt;

&lt;p&gt;Additionally, in case you were not aware, the ephemeralForTest SE has been replaced by the BiggieSE starting from version 5.0.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Yuan&lt;/p&gt;</comment>
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                            <attachment id="429693" name="core.34722.gz" size="11902628" author="luc.vidal@360learning.com" created="Thu, 2 Feb 2023 15:46:14 +0000"/>
                            <attachment id="429692" name="core.36392.gz" size="9750973" author="luc.vidal@360learning.com" created="Thu, 2 Feb 2023 15:46:13 +0000"/>
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