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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-65159] Consider {a: 1, b: 1} index to satisfy sort on {a: 1, b: -1}</title>
                <link>https://jira.mongodb.org/browse/SERVER-65159</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;There are two kinds of query plans we may consider here other than a full blocking sort:&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;For each distinct value of a (in order ascending), scan the entire b sub-range in the reverse direction. This would be a streaming plan.&lt;/li&gt;
	&lt;li&gt;For each distinct value of a (in order ascending), scan the entire b sub-range in order but put them into a blocking sort for just that sub-range. This should reverse them all but keep the disk accesses sequential. This is semi-streaming in that it doesn&apos;t need to block for all results, but will stop and start blocking for each &quot;a&quot; value.&lt;/li&gt;
&lt;/ol&gt;


&lt;p&gt;Either of these plans will involve a high number of seek calls if &quot;a&quot; is high cardinality, which could make them not worth it compared to a blocking sort plan. The first plan would be better for very low &quot;a&quot; cardinality, and the second would be better for when there are very few number of &quot;b&quot; values per value of &quot;a&quot;. So such plans would need to be considered with the query planner, ideally in a cost-based manner since our current cost model doesn&apos;t seem like it would take into account that the non-linear data accesses would be more expensive.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2014056">SERVER-65159</key>
            <summary>Consider {a: 1, b: 1} index to satisfy sort on {a: 1, b: -1}</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="charlie.swanson@mongodb.com">Charlie Swanson</reporter>
                        <labels>
                    </labels>
                <created>Fri, 1 Apr 2022 11:26:53 +0000</created>
                <updated>Mon, 5 Dec 2022 20:22:43 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="5001391" author="david.percy" created="Tue, 22 Nov 2022 18:13:14 +0000"  >&lt;p&gt;I think we&apos;ll be able to do this in Bonsai with recursive index navigation.  The outer loop scans forward producing unique values of &apos;a&apos;, and the inner loop scans backward to get all the (a, b) entries within that value of &apos;a&apos;.&lt;/p&gt;</comment>
                            <comment id="4926140" author="JIRAUSER1257467" created="Tue, 25 Oct 2022 17:03:33 +0000"  >&lt;p&gt;Sending to backlog since probably not a quick win, also might be something difficult for our current query planner to use effectively - We expect Bonsai to be needed before we work on this ticket&lt;/p&gt;</comment>
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            <issuekey id="1959735">SERVER-62405</issuekey>
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            <issuelink>
            <issuekey id="2118613">SERVER-69027</issuekey>
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