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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-15562] Estimate density before $near search</title>
                <link>https://jira.mongodb.org/browse/SERVER-15562</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Find the nearest point using $near with 2d index is slow in 2.7.8-pre- because we start from a small circle to search the documents, however that circle is proportional to the finest index level to guarantee we don&apos;t return too many on the first try. If the data is sparse, it takes several rounds to find the first document by expending the searching area exponentially.&lt;/p&gt;

&lt;p&gt;We can make it better by looking for the nearest document in its ancestor cell before the first search. Usually, this will give us a good estimate of the density. In S2, we look for such nearest document in the neighbors of closest vertex to this cell at coarser level.&lt;/p&gt;

&lt;p&gt;Find the nearest 100 points using $near with 2d index is slow because of the slowness in hashing function. &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-15576&quot; title=&quot;Floating-point inaccuracy when unhashing GeoHash to box&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-15576&quot;&gt;&lt;del&gt;SERVER-15576&lt;/del&gt;&lt;/a&gt; improves its performance by 20%.&lt;/p&gt;

&lt;hr /&gt;
&lt;p&gt;Original Title&lt;br/&gt;
Geo $near with 2d index query performance issue with 2.7.8-pre-&lt;/p&gt;

&lt;p&gt;Original Description&lt;/p&gt;

&lt;p&gt;When comparing performance of 2.7.8-pre vs 2.7.7, following query is 30-40% slower.&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;find({loc: {$near: [x, y]}}).limit(100)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt; 

&lt;p&gt;index is 2d geo index. please see attached svg for details.&lt;/p&gt;</description>
                <environment></environment>
        <key id="162524">SERVER-15562</key>
            <summary>Estimate density before $near search</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="siyuan.zhou@mongodb.com">Siyuan Zhou</assignee>
                                    <reporter username="rui.zhang">Rui Zhang</reporter>
                        <labels>
                            <label>28qa</label>
                    </labels>
                <created>Wed, 8 Oct 2014 08:30:38 +0000</created>
                <updated>Wed, 19 Nov 2014 16:26:07 +0000</updated>
                            <resolved>Thu, 30 Oct 2014 19:54:11 +0000</resolved>
                                    <version>2.7.8</version>
                                    <fixVersion>2.8.0-rc0</fixVersion>
                                    <component>Geo</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="752953" author="xgen-internal-githook" created="Thu, 30 Oct 2014 19:53:37 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;visualzhou&apos;, u&apos;name&apos;: u&apos;Siyuan Zhou&apos;, u&apos;email&apos;: u&apos;siyuan.zhou@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-15562&quot; title=&quot;Estimate density before $near search&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-15562&quot;&gt;&lt;del&gt;SERVER-15562&lt;/del&gt;&lt;/a&gt; Search neighbors for density estimation with 2d index&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/f5090f81588b684fc3cd27200ae6a822f16c37ae&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/f5090f81588b684fc3cd27200ae6a822f16c37ae&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="750973" author="xgen-internal-githook" created="Tue, 28 Oct 2014 22:19:55 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;visualzhou&apos;, u&apos;name&apos;: u&apos;Siyuan Zhou&apos;, u&apos;email&apos;: u&apos;siyuan.zhou@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-15562&quot; title=&quot;Estimate density before $near search&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-15562&quot;&gt;&lt;del&gt;SERVER-15562&lt;/del&gt;&lt;/a&gt; Estimate density before near search&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/385f03dc7205ef60bbb9cb8b475afd9c802bc67d&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/385f03dc7205ef60bbb9cb8b475afd9c802bc67d&lt;/a&gt;&lt;/p&gt;</comment>
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