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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-57116] Investigate improvements of JavaScript OOM issue with $function expression</title>
                <link>https://jira.mongodb.org/browse/SERVER-57116</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;A ticket investigated an OOM error of JavaScript engine when computing $function expression. The conclusion was that the cause of the problem is the garbage collection of the JavaScript engine in combination with the heap limit of 100MB.&lt;/p&gt;

&lt;p&gt;There were two workarounds proposed:&lt;/p&gt;

&lt;p&gt;1) process data in large collections in batches;&lt;/p&gt;

&lt;p&gt;2) increase the JS heap size. This is done on-prem via&lt;/p&gt;
&lt;p/&gt;
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&lt;p/&gt;
&lt;p&gt;This workaround is not applicable for users on Atlas due to authorisation issues.&#160;It is also not described in the public documentation.&lt;/p&gt;

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

&lt;p&gt;The purpose of this task is to investigate further improvements of the JS OOM issue, so that users don&apos;t experience it or have easier work-around. The following ideas were proposed and need further investigation:&lt;/p&gt;

&lt;p&gt;1) increase the default size of JS heap;&lt;/p&gt;

&lt;p&gt;2) add a heapSize parameter to $function expression which may allow for increasing the JS heap size per expression base (idea of &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=kevin.pulo&quot; class=&quot;user-hover&quot; rel=&quot;kevin.pulo&quot;&gt;kevin.pulo&lt;/a&gt;)&lt;/p&gt;

&lt;p&gt;3) make the GC more active, for instance by decreasing the current threshold that triggers GC from 80% to 70% of memory usage.&lt;/p&gt;

&lt;p&gt;4) provide better information for the issue:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;include the set parameter in the public documentation: advised agains by PM, since it creates opportunity for experimentation with sensitive parameters which are better protected.&lt;/li&gt;
&lt;/ul&gt;


&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;improve the error message for JS OOM, for instance add a hint to use the &apos;set parameter&apos; command or the heapSize parameter if 2) is implemented.&lt;/li&gt;
&lt;/ul&gt;


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

&lt;p&gt;These ideas could be helpful also for the coming project to upgrade the JavaScript engine.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="1742787">SERVER-57116</key>
            <summary>Investigate improvements of JavaScript OOM issue with $function expression</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-execution">Backlog - Query Execution</assignee>
                                    <reporter username="milena.ivanova@mongodb.com">Milena Ivanova</reporter>
                        <labels>
                    </labels>
                <created>Fri, 21 May 2021 10:10:41 +0000</created>
                <updated>Tue, 6 Dec 2022 01:17:31 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>9</watches>
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