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    <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-80735] [CQF] Lazy simplification </title>
                <link>https://jira.mongodb.org/browse/SERVER-80735</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Currently the optimizer uses an aggressive simplification strategy for its interval and PSR expressions. Consider the following workflow:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;A filter or eval expression is translated into a PSR.&lt;/li&gt;
	&lt;li&gt;On every non-trivial path element (composem or -a) the two trees are merged and simplified.&lt;/li&gt;
	&lt;li&gt;After the translation is complete, the paths are simplified and the intervals are intersected. This happens in both the substitution and exploration phase.&lt;/li&gt;
	&lt;li&gt;If there are multiple filters and/or multiple evaluation nodes, those are separately translated and their expressions merged and simplified sequentially.&lt;/li&gt;
	&lt;li&gt;Candidate indexes are computed every time we create a sargable node.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;Pros and cons:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Easier to debug and justify correctness.&lt;/li&gt;
	&lt;li&gt;All expressions are always kept as DNF.&lt;/li&gt;
&lt;/ul&gt;


&lt;ul&gt;
	&lt;li&gt;Easier not to defer decisions regarding overly complex predicates.&lt;/li&gt;
&lt;/ul&gt;


&lt;ul&gt;
	&lt;li&gt;Cons: can lead to quadratic simplification algorithms when we repeatedly use &quot;merge-and-simplify&quot; pattern.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;Proposal: lazy simplification.&lt;/p&gt;

&lt;ul&gt;
	&lt;li&gt;Introduce a new &quot;simplification&quot; rewrite, with a high numeric priority, to be executed after all the other simplification rewrites in the substitution phase.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;&#160; * Do not simplify expressions as they are translated from filter/eval nodes (just combine with a conjunction/disjunction node). Thus the expressions may no longer be in DNF/CNF.&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Do not compute candidate indexes until the final rewrite.&lt;/li&gt;
	&lt;li&gt;The final rewrite will do the following: convert expressions to DNF, simplify, and compute candidate indexes.&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="2434149">SERVER-80735</key>
            <summary>[CQF] Lazy simplification </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="svilen.mihaylov@mongodb.com">Svilen Mihaylov</reporter>
                        <labels>
                            <label>M9</label>
                    </labels>
                <created>Tue, 5 Sep 2023 14:42:09 +0000</created>
                <updated>Tue, 16 Jan 2024 11:01:19 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>7</watches>
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