<!-- 
RSS generated by JIRA (9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66) at Thu Feb 08 02:56:00 UTC 2024

It is possible to restrict the fields that are returned in this document by specifying the 'field' parameter in your request.
For example, to request only the issue key and summary append 'field=key&field=summary' to the URL of your request.
-->
<rss version="0.92" >
<channel>
    <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-1078] $elemMatch index scanning large numbers of rows</title>
                <link>https://jira.mongodb.org/browse/SERVER-1078</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt; I have an index on multiple columns - the last of which is a sort. The penultimate column in the index has very low cardinality - say 3,000 out of 5m records, is unlikely to go above 5,000 or so. When running an explain, the index is used, but mongo is doing a scan on 240k records to find out that only 343 of them have @fields.current.value : 1, despite that being in the index. If I remove that column from the index, I get exactly the same results as if it&apos;s there. However removing the column from the query it runs about three times faster. To me it seems like that part of the index ought to be used.&lt;/p&gt;

&lt;p&gt;Explain:&lt;/p&gt;

&lt;p&gt;&amp;gt; db.fields_current.node.find({ &apos;status&apos;: 1, &apos;@fields&apos;: { &apos;$elemMatch&apos;: &lt;/p&gt;
{ &apos;ex_node_group.value&apos;: 1, &apos;edition.tid&apos;: 369, &apos;channel.tid&apos;: 1, &apos;current.value&apos;: 1 }
&lt;p&gt; } }).sort( &lt;/p&gt;
{ &apos;@fields.pageviews.value&apos;: -1 }
&lt;p&gt;).hint(&apos;content_list_homepage_popular_index&apos;).explain();&lt;br/&gt;
{&lt;br/&gt;
	&quot;cursor&quot; : &quot;BtreeCursor content_list_homepage_popular_index&quot;,&lt;br/&gt;
	&quot;indexBounds&quot; : [&lt;br/&gt;
		[&lt;br/&gt;
			{&lt;br/&gt;
				&quot;@fields.edition.tid&quot; : 369,&lt;br/&gt;
				&quot;@fields.ex_node_group.value&quot; : 1,&lt;br/&gt;
				&quot;status&quot; : 1,&lt;br/&gt;
				&quot;@fields.current.value&quot; : 1,&lt;br/&gt;
				&quot;@fields.pageviews.value&quot; : &lt;/p&gt;
{
					&quot;$maxElement&quot; : 1
				}
&lt;p&gt;			},&lt;br/&gt;
			{&lt;br/&gt;
				&quot;@fields.edition.tid&quot; : 369,&lt;br/&gt;
				&quot;@fields.ex_node_group.value&quot; : 1,&lt;br/&gt;
				&quot;status&quot; : 1,&lt;br/&gt;
				&quot;@fields.current.value&quot; : 1,&lt;br/&gt;
				&quot;@fields.pageviews.value&quot; : &lt;/p&gt;
{
					&quot;$minElement&quot; : 1
				}
&lt;p&gt;			}&lt;br/&gt;
		]&lt;br/&gt;
	],&lt;br/&gt;
	&quot;nscanned&quot; : 240011,&lt;br/&gt;
	&quot;nscannedObjects&quot; : 240011,&lt;br/&gt;
	&quot;n&quot; : 343,&lt;br/&gt;
	&quot;millis&quot; : 1474&lt;br/&gt;
}&lt;br/&gt;
&amp;gt; db.fields_current.node.find({ &apos;status&apos;: 1, &apos;@fields&apos;: { &apos;$elemMatch&apos;: &lt;/p&gt;
{ &apos;ex_node_group.value&apos;: 1, &apos;edition.tid&apos;: 369, &apos;channel.tid&apos;: 1, &apos;current.value&apos;: 1 }
&lt;p&gt; } }).count();                                                                            &lt;br/&gt;
343&lt;br/&gt;
&amp;gt; db.fields_current.node.find({ &apos;status&apos;: 1, &apos;@fields&apos;: { &apos;$elemMatch&apos;: &lt;/p&gt;
{ &apos;ex_node_group.value&apos;: 1, &apos;edition.tid&apos;: 369, &apos;channel.tid&apos;: 1}
&lt;p&gt; } }).count();                     &lt;br/&gt;
64545&lt;br/&gt;
&amp;gt;&lt;/p&gt;</description>
                <environment></environment>
        <key id="11881">SERVER-1078</key>
            <summary>$elemMatch index scanning large numbers of rows</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="4">Incomplete</resolution>
                                        <assignee username="aaron">Aaron Staple</assignee>
                                    <reporter username="catch">Nathaniel Catchpole</reporter>
                        <labels>
                    </labels>
                <created>Mon, 3 May 2010 13:17:10 +0000</created>
                <updated>Fri, 7 Mar 2014 00:57:13 +0000</updated>
                            <resolved>Thu, 7 Mar 2013 17:21:50 +0000</resolved>
                                    <version>1.4.2</version>
                                                    <component>Querying</component>
                                        <votes>4</votes>
                                    <watches>5</watches>
                                                                                                                <comments>
                            <comment id="283531" author="aaron" created="Thu, 7 Mar 2013 17:21:16 +0000"  >&lt;p&gt;It is hard to diagnose an example from such an old version of the software, and without more information on the documents stored in the test collection.&lt;/p&gt;

&lt;p&gt;We have recently added some performance improvements for $elemMatch&lt;br/&gt;
&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4180&quot; title=&quot;Allow multiple constraints (on same field) within a $elemMatch clause to be used with a multikey index&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4180&quot;&gt;&lt;del&gt;SERVER-4180&lt;/del&gt;&lt;/a&gt;&lt;br/&gt;
&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-3104&quot; title=&quot;index bound improvements for elemMatch query on multikey index&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-3104&quot;&gt;&lt;del&gt;SERVER-3104&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;More work optimizing $elemMatch remains though, for example&lt;br/&gt;
&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-7509&quot; title=&quot;Combine index ranges for dotted fields within a $elemMatch expression, when possible&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-7509&quot;&gt;&lt;del&gt;SERVER-7509&lt;/del&gt;&lt;/a&gt;&lt;br/&gt;
&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-6050&quot; title=&quot;Consider allowing $elemMatch applied to non arrays&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-6050&quot;&gt;&lt;del&gt;SERVER-6050&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
                    <attachments>
                    </attachments>
                <subtasks>
                    </subtasks>
                <customfields>
                                                <customfield id="customfield_10050" key="com.atlassian.jira.toolkit:comments">
                        <customfieldname># Replies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1.0</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                <customfield id="customfield_10055" key="com.atlassian.jira.ext.charting:firstresponsedate">
                        <customfieldname>Date of 1st Reply</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>Thu, 7 Mar 2013 17:21:16 +0000</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10052" key="com.atlassian.jira.toolkit:dayslastcommented">
                        <customfieldname>Days since reply</customfieldname>
                        <customfieldvalues>
                                        10 years, 49 weeks, 6 days ago
    
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_18254" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Dependencies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue><![CDATA[]]></customfieldvalue>


                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_15850" key="com.atlassian.jira.plugins.jira-development-integration-plugin:devsummary">
                        <customfieldname>Development</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    <customfield id="customfield_10057" key="com.atlassian.jira.toolkit:lastusercommented">
                        <customfieldname>Last comment by Customer</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>true</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_10056" key="com.atlassian.jira.toolkit:lastupdaterorcommenter">
                        <customfieldname>Last commenter</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>ian@mongodb.com</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_11151" key="com.atlassian.jira.toolkit:LastCommentDate">
                        <customfieldname>Last public comment date</customfieldname>
                        <customfieldvalues>
                            10 years, 49 weeks, 6 days ago
                        </customfieldvalues>
                    </customfield>
                                                                                                                        <customfield id="customfield_10000" key="com.atlassian.jira.plugin.system.customfieldtypes:radiobuttons">
                        <customfieldname>Old_Backport</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="10000"><![CDATA[No]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                            <customfield id="customfield_10051" key="com.atlassian.jira.toolkit:participants">
                        <customfieldname>Participants</customfieldname>
                        <customfieldvalues>
                                        <customfieldvalue>aaron</customfieldvalue>
            <customfieldvalue>catch</customfieldvalue>
    
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                        <customfield id="customfield_14254" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Product Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|hrpmun:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                <customfield id="customfield_12550" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>2|hric1z:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10558" key="com.pyxis.greenhopper.jira:gh-global-rank">
                        <customfieldname>Rank (Obsolete)</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>20602</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_23361" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Requested By</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            <customfield id="customfield_10053" key="com.atlassian.jira.ext.charting:timeinstatus">
                        <customfieldname>Time In Status</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                        <customfield id="customfield_22870" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Triagers</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                    <customfield id="customfield_14350" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>serverRank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|hszy7z:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                    </customfields>
    </item>
</channel>
</rss>