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        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-57062] Improve memory footprint of document/value caching in window functions</title>
                <link>https://jira.mongodb.org/browse/SERVER-57062</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;As part of the &lt;a href=&quot;https://github.com/mongodb/mongo/commit/be41c9d532346c873c5b909a18fe92e8885337cb&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;commit to account for freed documents&lt;/a&gt; when they fall out of a window, we made an unfortunate compromise to handle the inflation of the internal Document cache by &lt;a href=&quot;https://github.com/mongodb/mongo/blob/be41c9d532346c873c5b909a18fe92e8885337cb/src/mongo/db/pipeline/window_function/partition_iterator.cpp#L477&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;forcing all fields to be cached up front&lt;/a&gt;. This is not efficient and may end up forcing a spill to disk more often than necessary. Several options discussed to avoid doing this for every document:&lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;Use the required fields from the dependency analysis to only populate the Document cache for the fields we need. Note that if a required field lands on an object, some expressions (e.g. $max) will recurse into the nested object to do a field-by-field comparison.&lt;/li&gt;
	&lt;li&gt;Detect the changing in memory footprint on each expression evaluation. This one is tedious and likely to break if we were to add more functions or window types.&lt;/li&gt;
	&lt;li&gt;Temporarily turn off caching in Document while the $setWindowFields stage is holding onto it, since the stage will eventually project a new field it should not affect performance. This could be interesting to try but may be invasive.&lt;/li&gt;
	&lt;li&gt;Add a callback to Document when a field is added to the cache, such that window functions can adjust its memory tracking in near real-time&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="1731249">SERVER-57062</key>
            <summary>Improve memory footprint of document/value caching in window functions</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="nicholas.zolnierz@mongodb.com">Nicholas Zolnierz</reporter>
                        <labels>
                    </labels>
                <created>Wed, 19 May 2021 13:12:17 +0000</created>
                <updated>Tue, 6 Dec 2022 01:17:53 +0000</updated>
                                                                                                <votes>1</votes>
                                    <watches>3</watches>
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            <issuekey id="1744053">SERVER-57130</issuekey>
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