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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-13618] Optimization for sorted $in queries not applied to reverse sort order</title>
                <link>https://jira.mongodb.org/browse/SERVER-13618</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;div class=&quot;panel&quot; style=&quot;background-color: #EEEEEE;border-color: #ccc;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;border-bottom-color: #ccc;background-color: #6CB33F;&quot;&gt;&lt;b&gt;Issue Status as of April 21, 2014&lt;/b&gt;&lt;/div&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #EEEEEE;&quot;&gt;
&lt;p&gt;&lt;b&gt;ISSUE SUMMARY&lt;/b&gt;&lt;br/&gt;
Queries using &lt;tt&gt;$in&lt;/tt&gt; and &lt;tt&gt;.sort()&lt;/tt&gt; can be handled efficiently by &quot;exploding&quot; the index bounds of the &lt;tt&gt;$in&lt;/tt&gt; predicates and creating several child index scans. In the case where the sort order is reversed from the index spec the query planner adds a blocking sort stage at the end, which impacts the performance and can be avoided.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;USER IMPACT&lt;/b&gt;&lt;br/&gt;
If users rely on these kinds of queries with &lt;tt&gt;$in&lt;/tt&gt; and sort, they can experience slower than expected query results in some cases. If the size of returned documents exceeds the limit of 32MB, the query fails with an error.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;WORKAROUNDS&lt;/b&gt;&lt;br/&gt;
If only the reverse sort order is required, the index can be re-created with the last field order reversed. If both sort orders are required, no workaround is known.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;RESOLUTION&lt;/b&gt;&lt;br/&gt;
The query planner now correctly detects the reverse sort order and does not sort the documents in memory anymore.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;AFFECTED VERSIONS&lt;/b&gt;&lt;br/&gt;
Version 2.6.0 is affected by this bug.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;PATCHES&lt;/b&gt;&lt;br/&gt;
The patch is included in the 2.6.1 production release.&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h6&gt;&lt;a name=&quot;Originaldescription&quot;&gt;&lt;/a&gt;Original description&lt;/h6&gt;

&lt;p&gt;Say we have index {a: 1, b: 1, c: 1} and we issue the following query:&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;t.find({a: {$in: [1, 2]}, b: {$in: [3, 4]}}).sort({c: 1});&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;The explode for scans hack (see &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-1205&quot; title=&quot;$or sort does not use index ranges expressed in or clauses&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-1205&quot;&gt;&lt;del&gt;SERVER-1205&lt;/del&gt;&lt;/a&gt;), is able to avoid a blocking sort stage for this query by merge sorting over four child index scans with the following bounds:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;a: [[1, 1]], b: [[3, 3]]&lt;/li&gt;
	&lt;li&gt;a: [[1, 1]], b: [[4, 4]]&lt;/li&gt;
	&lt;li&gt;a: [[2, 2]], b: [[3, 3]]&lt;/li&gt;
	&lt;li&gt;a: [[2, 2]], b: [[4, 4]]&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;We should be able to do the same thing for query&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;t.find({a: {$in: [1, 2]}, b: {$in: [3, 4]}}).sort({c: -1});&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;simply by reversing the direction of the index scans. However, explodeForSort() fails and we end up creating a plan with a blocking sort for the query with .sort({c: -1}).&lt;/p&gt;</description>
                <environment></environment>
        <key id="131577">SERVER-13618</key>
            <summary>Optimization for sorted $in queries not applied to reverse sort order</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="david.storch@mongodb.com">David Storch</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                    </labels>
                <created>Wed, 16 Apr 2014 18:32:57 +0000</created>
                <updated>Mon, 11 Jul 2016 17:17:44 +0000</updated>
                            <resolved>Thu, 17 Apr 2014 17:13:26 +0000</resolved>
                                    <version>2.6.0</version>
                                    <fixVersion>2.6.1</fixVersion>
                    <fixVersion>2.7.0</fixVersion>
                                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="553365" author="xgen-internal-githook" created="Thu, 17 Apr 2014 17:27:27 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;dstorch&apos;, u&apos;name&apos;: u&apos;David Storch&apos;, u&apos;email&apos;: u&apos;david.storch@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13618&quot; title=&quot;Optimization for sorted $in queries not applied to reverse sort order&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13618&quot;&gt;&lt;del&gt;SERVER-13618&lt;/del&gt;&lt;/a&gt; explode for sort tries reversing index scan direction&lt;br/&gt;
(cherry picked from commit ce52f313ca52759d606886641f44541bd7baf5bd)&lt;br/&gt;
Branch: v2.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/eeef3c3ded2d8d55345af8b11041bafae8783958&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/eeef3c3ded2d8d55345af8b11041bafae8783958&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="553330" author="xgen-internal-githook" created="Thu, 17 Apr 2014 17:12:00 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;dstorch&apos;, u&apos;name&apos;: u&apos;David Storch&apos;, u&apos;email&apos;: u&apos;david.storch@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13618&quot; title=&quot;Optimization for sorted $in queries not applied to reverse sort order&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13618&quot;&gt;&lt;del&gt;SERVER-13618&lt;/del&gt;&lt;/a&gt; explode for sort tries reversing index scan direction&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/ce52f313ca52759d606886641f44541bd7baf5bd&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/ce52f313ca52759d606886641f44541bd7baf5bd&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
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                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                                        </outwardlinks>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="131525">SERVER-13611</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="12097">SERVER-1205</issuekey>
        </issuelink>
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