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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-14197] Case insensitive left-anchored regular expressions whose first few characters are non-special and ASCII don&apos;t need to do full index scans</title>
                <link>https://jira.mongodb.org/browse/SERVER-14197</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Case insensitive left-anchored regular expressions whose first few characters are non-special and ASCII don&apos;t need to do full index scans, but can be exploded out to 2^n range queries with regex filters where n is the number of non-special characters at the beginning of the regex.&lt;/p&gt;

&lt;p&gt;For example, this 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;db.foo.find( { s : /^ab/i } );&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
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&lt;p/&gt;

&lt;p&gt;could be converted in mongod to anything functionally equivalent to&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;db.foo.find({&quot;$or&quot;: [ { s : /^ab/ }, { s : /^Ab/ }, { s : /^aB/ }, { s : /^AB/ } ] );&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;(However, I do not specifically request that the mongod actually run that $or query, just anything analogous to it.)&lt;/p&gt;

&lt;p&gt;Obviously the exponential explosion in disjuncts would be undesirable for sufficiently long prefixes, but perhaps an expansion of the first few characters&apos; worth could be a win for people compared the full index scan we currently do.&lt;/p&gt;

&lt;p&gt;(In this issue I restrict the request to just left anchored regular expressions corresponding to a prefix of ASCII characters because restricting the problem just to ASCII strings reduces the complexity of implementation and perhaps maintenance. This is not intended to be a substitute for introduction of any locale aware, case insensitive collations, just an optimization request for a feature that&apos;s unlikely to go away even if we do grow locale awareness.)&lt;/p&gt;

&lt;p&gt;Testing: presumably this improvement would somehow be reflected in the explain() plan. So certain aspects of testing could include comparing explain plains from case-sensitive and case-insensitive regular expression queries.&lt;/p&gt;

&lt;p&gt;Documentation changes needed: if we document the absence of optimizations for case-insensitive regular expressions, we should cease to do so if this improvement is made. (Whether we also document the existence of the new optimization is a separate question about which I have no opinion.)&lt;/p&gt;

</description>
                <environment></environment>
        <key id="140916">SERVER-14197</key>
            <summary>Case insensitive left-anchored regular expressions whose first few characters are non-special and ASCII don&apos;t need to do full index scans</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="richard.kreuter">Richard Kreuter</reporter>
                        <labels>
                    </labels>
                <created>Fri, 6 Jun 2014 22:13:25 +0000</created>
                <updated>Tue, 28 Nov 2023 19:30:57 +0000</updated>
                                                                            <component>Querying</component>
                                        <votes>1</votes>
                                    <watches>16</watches>
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                                        <issuelink>
            <issuekey id="1385642">SERVER-49002</issuekey>
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