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    <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>[DOCS-12025] Docs for SERVER-13201: Allow new Aggregation $out operator to explicitly name a DB to write to</title>
                <link>https://jira.mongodb.org/browse/DOCS-12025</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;
&lt;div class=&quot;panel&quot; style=&quot;background-color: #cccccc;border-style: dashed;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #cccccc;&quot;&gt;
&lt;h3&gt;&lt;a name=&quot;Description%3A&quot;&gt;&lt;/a&gt;Description: &lt;/h3&gt;

&lt;p&gt;Yes, you can now $out to a different database via the &quot;db&quot; option in the $out specification. &quot;db&quot; is optional; the default value is the same database as the aggregation.&lt;/p&gt;

&lt;p&gt;See the $out design and the syntax for more details.&lt;/p&gt;

&lt;h3&gt;&lt;a name=&quot;EngineeringTicketDescription%3A&quot;&gt;&lt;/a&gt;Engineering Ticket Description:&lt;/h3&gt;

&lt;p&gt;Using 2.6.0rc1 (Linux x86-64) I&apos;ve been doing some research into speeding up some Aggregation use cases via Parallelisation. For the full investigation see here: &lt;a href=&quot;http://pauldone.blogspot.co.uk/2014/03/mongoparallelaggregation.html&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://pauldone.blogspot.co.uk/2014/03/mongoparallelaggregation.html&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;One of the main outcomes, was although a good speed-up can be achieved with multiple threads each running aggregate() on a subset of the collection&apos;s data, the main thing holding back further performance improvement was the threads queueing to write out to result collections in the same database, queueing for the DB write-lock.&lt;/p&gt;

&lt;p&gt;In the tests, the $out operator &lt;a href=&quot;http://docs.mongodb.org/master/reference/operator/aggregation/out/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://docs.mongodb.org/master/reference/operator/aggregation/out/&lt;/a&gt; is being used to specify different output collection for each thread&apos;s aggregate() invocation. However the $out operator does not allow one to specify a named database, in addition to a named collection. As a result, the same database as the aggregation&apos;s source collection is assumed and it&apos;s not possible to use different databases, to remove the write-lock bottleneck for such use cases.&lt;/p&gt;

&lt;p&gt;Please consider enhancing the $out operator to support declaring a target database in addition to a target collection, in a similar manner to how this can already be achieved today in MongoDB&apos;s MapReduce function (specifically the mapReduce() function&apos;s &apos;out&apos; option - &lt;a href=&quot;http://docs.mongodb.org/manual/reference/method/db.collection.mapReduce/#mapreduce-out-mtd&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://docs.mongodb.org/manual/reference/method/db.collection.mapReduce/#mapreduce-out-mtd&lt;/a&gt; )&lt;/p&gt;

&lt;p&gt;Thanks Paul&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;


&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="599454">DOCS-12025</key>
            <summary>Docs for SERVER-13201: Allow new Aggregation $out operator to explicitly name a DB to write to</summary>
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                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="13201">Fixed</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="kay.kim@mongodb.com">Kay Kim</reporter>
                        <labels>
                            <label>usability</label>
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                <created>Tue, 4 Sep 2018 20:18:01 +0000</created>
                <updated>Mon, 13 Nov 2023 18:31:41 +0000</updated>
                            <resolved>Mon, 1 Oct 2018 16:23:09 +0000</resolved>
                                                    <fixVersion>4.1.3</fixVersion>
                    <fixVersion>Server_Docs_20231030</fixVersion>
                    <fixVersion>Server_Docs_20231106</fixVersion>
                    <fixVersion>Server_Docs_20231105</fixVersion>
                    <fixVersion>Server_Docs_20231113</fixVersion>
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