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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-70780] [CQF] Simplify redundant PathObj / impossible PathArr</title>
                <link>https://jira.mongodb.org/browse/SERVER-70780</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Take this $elemMatch predicate:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;{a: {$elemMatch: {b: 2, c: 3}}}&lt;/span&gt;&lt;/pre&gt;
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		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
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&lt;p/&gt;

&lt;p&gt;It expands to this ABT:&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;
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				&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;   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;|   PathGet [a]&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   PathTraverse [1]&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   PathComposeM []&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   |   PathComposeA []&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   |   |   PathArr []&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   |   PathObj []&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   PathComposeM []&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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;   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;|   |   PathGet [c] PathTraverse [1] PathCompare [Eq] Const [3]&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&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-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;|   PathGet [b] PathTraverse [1] PathCompare [Eq] Const [2]&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 last 3 lines correspond to &lt;tt&gt;b: 2, c: 3&lt;/tt&gt;.  This predicate can only be true when applied to an object.  So the extra PathObj / PathArr checks are redundant: we can replace them with true / false respectively.&lt;/p&gt;

&lt;p&gt;It&apos;s not enough to check for a PathGet however.  A predicate like &lt;tt&gt;b: {$exists: false&lt;/tt&gt;} can be true when applied to a non-object, because it uses PathDefault which can &quot;catch&quot; Nothing.  Other nodes like this include PathConstant and PathLambda.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2164590">SERVER-70780</key>
            <summary>[CQF] Simplify redundant PathObj / impossible PathArr</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-query-optimization">Backlog - Query Optimization</assignee>
                                    <reporter username="david.percy@mongodb.com">David Percy</reporter>
                        <labels>
                            <label>Ideas</label>
                            <label>bonsai-onboarding</label>
                            <label>optimization</label>
                    </labels>
                <created>Fri, 21 Oct 2022 21:40:44 +0000</created>
                <updated>Mon, 12 Jun 2023 21:27:44 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="5468509" author="david.percy" created="Thu, 1 Jun 2023 19:26:59 +0000"  >&lt;p&gt;Initially I thought we should solve this by adding an optimization that takes an ABT and simplifies it.  But it looks kind of complicated to detect whether the PathObj is redundant:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;We have to notice that &lt;tt&gt;PathGet &lt;span class=&quot;error&quot;&gt;&amp;#91;c&amp;#93;&lt;/span&gt; ...&lt;/tt&gt; and &lt;tt&gt;PathObj&lt;/tt&gt; both take the same input, even though they aren&apos;t direct siblings.&lt;/li&gt;
	&lt;li&gt;We have to check that &lt;tt&gt;PathGet &lt;span class=&quot;error&quot;&gt;&amp;#91;c&amp;#93;&lt;/span&gt; ...&lt;/tt&gt; is only true for objects.
	&lt;ul&gt;
		&lt;li&gt;We have to check that its &lt;tt&gt;PathTraverse ...&lt;/tt&gt; child is never true for Nothing.
		&lt;ul&gt;
			&lt;li&gt;We have to check that its &lt;tt&gt;PathCompare ...&lt;/tt&gt; child is never true for Nothing&lt;/li&gt;
		&lt;/ul&gt;
		&lt;/li&gt;
	&lt;/ul&gt;
	&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;This starts to resemble type checking, which we probably should think about more holistically.&lt;/p&gt;

&lt;hr /&gt;

&lt;p&gt;So instead, maybe we can look at how we translate $elemMatch to ABT, and try to avoid creating the redundant nodes in the first place.&lt;/p&gt;

&lt;p&gt;Maybe &quot;object elemMatch&quot; never needs the PathArr?  Maybe that PathArr is only used for nested elemMatch?&lt;/p&gt;</comment>
                    </comments>
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                    <name>Related</name>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="2351026">SERVER-77499</issuekey>
        </issuelink>
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