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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-21063] MongoDB with WiredTiger can build very deep trees</title>
                <link>https://jira.mongodb.org/browse/SERVER-21063</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Under certain circumstances, MongoDB + WT can build very deep trees. This has a considerable performance impact as the tree depth will equate with increased work when looking for a leaf page.&lt;/p&gt;</description>
                <environment></environment>
        <key id="235615">SERVER-21063</key>
            <summary>MongoDB with WiredTiger can build very deep trees</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="9">Done</resolution>
                                        <assignee username="michael.cahill@mongodb.com">Michael Cahill</assignee>
                                    <reporter username="david.hows">David Hows</reporter>
                        <labels>
                            <label>WTplaybook</label>
                    </labels>
                <created>Thu, 22 Oct 2015 00:12:26 +0000</created>
                <updated>Tue, 16 Nov 2021 14:10:22 +0000</updated>
                            <resolved>Fri, 13 Nov 2015 06:38:31 +0000</resolved>
                                    <version>3.0.6</version>
                    <version>3.0.7</version>
                                    <fixVersion>3.0.8</fixVersion>
                                    <component>WiredTiger</component>
                                        <votes>1</votes>
                                    <watches>16</watches>
                                                                                                                <comments>
                            <comment id="1148135" author="david.hows" created="Wed, 20 Jan 2016 01:04:54 +0000"  >&lt;p&gt;Correct. You will need to rebuild the collection. Performing a resync on the repl member is also an option, but may be overkill.&lt;/p&gt;</comment>
                            <comment id="1148129" author="tim.thawkins@gmail.com" created="Wed, 20 Jan 2016 00:55:27 +0000"  >&lt;p&gt;Presumably from above, that the safest course of action after determining that a collection is still impacted post 3.0.8 upgrade, would be to dump the collection, drop it, and then reload it?&lt;/p&gt;

</comment>
                            <comment id="1148015" author="david.hows" created="Tue, 19 Jan 2016 23:09:47 +0000"  >&lt;p&gt;Hi All,&lt;/p&gt;

&lt;p&gt;Just wanted to clarify a few minor details with regard to this issue.&lt;/p&gt;

&lt;p&gt;In MongoDB with WiredTiger both collection &lt;em&gt;and&lt;/em&gt; index data are stored in btree structures. At this stage, it has been more common for the collection data to experience this issue than the MongoDB indexes. &lt;/p&gt;

&lt;p&gt;When running the &lt;tt&gt;.stats()&lt;/tt&gt; command as suggested by Stuart H above the btree details seen in the output will be for the collection data only. You can see the stats for a given collection by running stats with the &lt;tt&gt;indexDetails&lt;/tt&gt; option as below:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;db.foo.stats({indexDetails:true})&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;</comment>
                            <comment id="1146964" author="stuart.hall@masternaut.com" created="Tue, 19 Jan 2016 09:07:48 +0000"  >&lt;p&gt;Hi Timothy,&lt;/p&gt;

&lt;blockquote&gt;
&lt;p&gt;Identify collections with indexes that are impacted by this issue:&lt;/p&gt;&lt;/blockquote&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;db.&amp;lt;collection name&amp;gt;.stats( ).wiredTiger.btree[&lt;/span&gt;&lt;span style=&quot;color: blue; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;&quot;maximum tree depth&quot;&lt;/span&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;];&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;
&lt;p&gt;This should be a small number (&amp;lt; 10). We&apos;ve seen values approaching 1000 on large collections with versions &amp;lt; 3.0.8&lt;/p&gt;

&lt;blockquote&gt;
&lt;p&gt;After an upgrade to 3.0.8 containing the fix, forcing an update to the indexes to rebuild the trees.:&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;I&apos;m afraid that you need to do a wipe and rebuild of the associated node. I assume that a repair would do this, but if you use replica sets, it&apos;s usually easier to stop one node, wipe the data files, and then restart it, allowing it to rebuild from another node in the replica set. Unfortunately, there is no other way to do this as this bug actually affects how the data is stored within wiredTiger.&lt;/p&gt;

&lt;p&gt;Regards,&lt;/p&gt;

&lt;p&gt;Stuart H.&lt;br/&gt;
(Disclaimer: I am not a MongoDB employee but was involved with the reporting and fixing of the original issue)&lt;/p&gt;</comment>
                            <comment id="1146950" author="tim.thawkins@gmail.com" created="Tue, 19 Jan 2016 08:44:12 +0000"  >&lt;p&gt;We are running 3.0.6&lt;/p&gt;

&lt;p&gt;What is the recommended method to: &lt;/p&gt;

&lt;p&gt;1. Identify collections with indexes that are impacted by this issue&lt;br/&gt;
2. After an upgrade to 3.0.8 containing the fix, forcing an update to the indexes to rebuild the trees. &lt;/p&gt;</comment>
                            <comment id="1109003" author="michael.cahill" created="Wed, 9 Dec 2015 01:40:27 +0000"  >&lt;p&gt;Yes, &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=zhifan&quot; class=&quot;user-hover&quot; rel=&quot;zhifan&quot;&gt;zhifan&lt;/a&gt;, collections created with 3.2 do not have this problem.&lt;/p&gt;

&lt;p&gt;Be aware that collections created by MongoDB version 3.0.7 and earlier that are unbalanced are not automatically repaired by switching to 3.2.  An initial sync may be required to create balanced trees.&lt;/p&gt;</comment>
                            <comment id="1108984" author="zhifan" created="Wed, 9 Dec 2015 00:56:11 +0000"  >&lt;p&gt;may I know if this issue is fixed in the just released version 3.2? &lt;/p&gt;</comment>
                            <comment id="1067501" author="xgen-internal-githook" created="Thu, 22 Oct 2015 00:25:48 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;michaelcahill&apos;, u&apos;name&apos;: u&apos;Michael Cahill&apos;, u&apos;email&apos;: u&apos;michael.cahill@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-21063&quot; title=&quot;MongoDB with WiredTiger can build very deep trees&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-21063&quot;&gt;&lt;del&gt;SERVER-21063&lt;/del&gt;&lt;/a&gt; Avoid creating deep trees for append-only workloads.&lt;/p&gt;

&lt;p&gt;Merge pull request #1988 from wiredtiger/split-deepen-for-append&lt;/p&gt;

&lt;p&gt;(cherry picked from commit a98417879da9eacefecd74242fd3924b46e31183)&lt;br/&gt;
Branch: mongodb-3.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/cb642366f168caadd56bed3c257e4d3e4c5cc4f0&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/cb642366f168caadd56bed3c257e4d3e4c5cc4f0&lt;/a&gt;&lt;/p&gt;</comment>
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