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    <title>MongoDB Jira</title>
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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-48935] how to using cover index for mongo count</title>
                <link>https://jira.mongodb.org/browse/SERVER-48935</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;hi:&lt;/p&gt;

&lt;p&gt;&#160; count collecitons record including read metadata and scan documents.&lt;/p&gt;

&lt;p&gt;read metadata is fast but exists problem. and not suggest.&lt;/p&gt;

&lt;p&gt;scan documents is good but slow.&lt;/p&gt;

&lt;p&gt;db.collection.aggregate(&lt;span class=&quot;error&quot;&gt;&amp;#91;\{$project:{_id:0}},\{$group:{_id:null,total:{$sum:1}}}&amp;#93;&lt;/span&gt;)&lt;/p&gt;

&lt;p&gt;but is collscan.is there using cover index ?&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;from document:it can use cover index:&lt;/p&gt;

&lt;p&gt;Changed in version 3.2:&#160;Starting in MongoDB 3.2, indexes can&#160;&lt;a href=&quot;https://docs.mongodb.com/manual/core/query-optimization/#read-operations-covered-query&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;cover&lt;/a&gt;&#160;an aggregation pipeline. In MongoDB 2.6 and 3.0, indexes could not cover an aggregation pipeline since even when the pipeline uses an index, aggregation still requires access to the actual documents.&lt;/p&gt;

&lt;p&gt;is there example for me?&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="1383364">SERVER-48935</key>
            <summary>how to using cover index for mongo count</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="-1">Unassigned</assignee>
                                    <reporter username="601290552@qq.com">jing xu</reporter>
                        <labels>
                    </labels>
                <created>Thu, 18 Jun 2020 03:21:00 +0000</created>
                <updated>Thu, 18 Jun 2020 15:07:52 +0000</updated>
                            <resolved>Thu, 18 Jun 2020 15:07:52 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="3214250" author="carl.champain" created="Thu, 18 Jun 2020 15:07:45 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=601290552%40qq.com&quot; class=&quot;user-hover&quot; rel=&quot;601290552@qq.com&quot;&gt;601290552@qq.com&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;The SERVER project is for bugs and feature suggestions for the MongoDB server. As this ticket does not appear to be a bug, I will now close it. If you need further assistance troubleshooting, I encourage you to ask our community by posting on the &lt;a href=&quot;http://community.mongodb.com/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;MongoDB Community Forums&lt;/a&gt; or on &lt;a href=&quot;https://stackoverflow.com/questions/tagged/mongodb&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;Stack Overflow with the &lt;tt&gt;mongodb&lt;/tt&gt; tag&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;Kind regards,&lt;br/&gt;
Carl&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</comment>
                            <comment id="3213657" author="601290552@qq.com" created="Thu, 18 Jun 2020 07:39:51 +0000"  >&lt;p&gt;using COLL_SCAN not using COUNT_SCAN.&lt;/p&gt;</comment>
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