<!-- 
RSS generated by JIRA (9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66) at Thu Feb 08 04:22:43 UTC 2024

It is possible to restrict the fields that are returned in this document by specifying the 'field' parameter in your request.
For example, to request only the issue key and summary append 'field=key&field=summary' to the URL of your request.
-->
<rss version="0.92" >
<channel>
    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <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>
    </build-info>


<item>
            <title>[SERVER-30111] Mapreduce uses global lock when outputting to empty collection</title>
                <link>https://jira.mongodb.org/browse/SERVER-30111</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I want to efficiently mapreduce some data and output to an empty collection without touching the global lock.&lt;/p&gt;

&lt;p&gt;There is an optimization in mr.cpp in postProcessCollectionNonAtomic which forces &quot;replace&quot; mode on outputting to empty collections.&lt;br/&gt;
Unfortunately, &quot;replace&quot; mode gets a global lock, even when writing to the same database.&lt;/p&gt;

&lt;p&gt;Both of these are unexpected.&lt;/p&gt;

&lt;p&gt;The workaround is to insert a dummy document into the empty collection, and output using &quot;merge&quot; mode. This is unintuitive and requires digging into the mongo core code.&lt;/p&gt;

&lt;p&gt;There is a blog post describing the issue and workaround here:&lt;br/&gt;
&lt;a href=&quot;http://venublog.com/2014/04/05/mongodb-map-reduce-how-to-avoid-global-locks&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://venublog.com/2014/04/05/mongodb-map-reduce-how-to-avoid-global-locks&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;The blog post is a few years old but this is still an issue in the master branch:&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/commands/mr.cpp#L643&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/master/src/mongo/db/commands/mr.cpp#L643&lt;/a&gt;&lt;/p&gt;</description>
                <environment></environment>
        <key id="403178">SERVER-30111</key>
            <summary>Mapreduce uses global lock when outputting to empty collection</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="3">Duplicate</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="james@rabb.it">James Mitchell</reporter>
                        <labels>
                    </labels>
                <created>Wed, 12 Jul 2017 17:35:09 +0000</created>
                <updated>Fri, 14 Jul 2017 21:24:07 +0000</updated>
                            <resolved>Fri, 14 Jul 2017 21:24:07 +0000</resolved>
                                    <version>3.2.15</version>
                    <version>3.4.6</version>
                    <version>3.5.9</version>
                                                    <component>MapReduce</component>
                                        <votes>0</votes>
                                    <watches>10</watches>
                                                                                                                <comments>
                            <comment id="1622654" author="ramon.fernandez" created="Fri, 14 Jul 2017 21:23:15 +0000"  >&lt;p&gt;Thanks for your report &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=james%40rabb.it&quot; class=&quot;user-hover&quot; rel=&quot;james@rabb.it&quot;&gt;james@rabb.it&lt;/a&gt;. This enhancement was previously requested in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13552&quot; title=&quot;remove unnecessary global lock during &amp;quot;replace&amp;quot; out action&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13552&quot;&gt;SERVER-13552&lt;/a&gt;, so I&apos;m going to mark this ticket as a duplicate. Please watch &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13552&quot; title=&quot;remove unnecessary global lock during &amp;quot;replace&amp;quot; out action&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13552&quot;&gt;SERVER-13552&lt;/a&gt; for updates.&lt;/p&gt;

&lt;p&gt;Regards,&lt;br/&gt;
Ram&#243;n.&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10010">
                    <name>Duplicate</name>
                                            <outwardlinks description="duplicates">
                                        <issuelink>
            <issuekey id="130553">SERVER-13552</issuekey>
        </issuelink>
                            </outwardlinks>
                                                        </issuelinktype>
                    </issuelinks>
                <attachments>
                    </attachments>
                <subtasks>
                    </subtasks>
                <customfields>
                                                <customfield id="customfield_10050" key="com.atlassian.jira.toolkit:comments">
                        <customfieldname># Replies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1.0</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                <customfield id="customfield_10055" key="com.atlassian.jira.ext.charting:firstresponsedate">
                        <customfieldname>Date of 1st Reply</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>Fri, 14 Jul 2017 21:23:15 +0000</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10052" key="com.atlassian.jira.toolkit:dayslastcommented">
                        <customfieldname>Days since reply</customfieldname>
                        <customfieldvalues>
                                        6 years, 30 weeks, 5 days ago
    
                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_18254" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Dependencies</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue><![CDATA[]]></customfieldvalue>


                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_15850" key="com.atlassian.jira.plugins.jira-development-integration-plugin:devsummary">
                        <customfieldname>Development</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    <customfield id="customfield_10057" key="com.atlassian.jira.toolkit:lastusercommented">
                        <customfieldname>Last comment by Customer</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>true</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_10056" key="com.atlassian.jira.toolkit:lastupdaterorcommenter">
                        <customfieldname>Last commenter</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>ramon.fernandez@mongodb.com</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_11151" key="com.atlassian.jira.toolkit:LastCommentDate">
                        <customfieldname>Last public comment date</customfieldname>
                        <customfieldvalues>
                            6 years, 30 weeks, 5 days ago
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                    <customfield id="customfield_10032" key="com.atlassian.jira.plugin.system.customfieldtypes:select">
                        <customfieldname>Operating System</customfieldname>
                        <customfieldvalues>
                                <customfieldvalue key="10026"><![CDATA[ALL]]></customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                <customfield id="customfield_10051" key="com.atlassian.jira.toolkit:participants">
                        <customfieldname>Participants</customfieldname>
                        <customfieldvalues>
                                        <customfieldvalue>james@rabb.it</customfieldvalue>
            <customfieldvalue>ramon.fernandez@mongodb.com</customfieldvalue>
    
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                        <customfield id="customfield_14254" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Product Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|htarpj:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                <customfield id="customfield_12550" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>Rank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>2|ht2nqf:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                <customfield id="customfield_10558" key="com.pyxis.greenhopper.jira:gh-global-rank">
                        <customfieldname>Rank (Obsolete)</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>9223372036854775807</customfieldvalue>
                        </customfieldvalues>
                    </customfield>
                                                                                            <customfield id="customfield_23361" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Requested By</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                            <customfield id="customfield_10750" key="com.atlassian.jira.plugin.system.customfieldtypes:textarea">
                        <customfieldname>Steps To Reproduce</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>&lt;p&gt;Create a mapreduce and output to an empty collection, and it will get the global lock.&lt;/p&gt;</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                    <customfield id="customfield_10053" key="com.atlassian.jira.ext.charting:timeinstatus">
                        <customfieldname>Time In Status</customfieldname>
                        <customfieldvalues>
                            
                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                                                                                                        <customfield id="customfield_22870" key="com.onresolve.jira.groovy.groovyrunner:scripted-field">
                        <customfieldname>Triagers</customfieldname>
                        <customfieldvalues>
                                

                        </customfieldvalues>
                    </customfield>
                                                                                                                                                                                                                                                                                                                                                                                    <customfield id="customfield_14350" key="com.pyxis.greenhopper.jira:gh-lexo-rank">
                        <customfieldname>serverRank</customfieldname>
                        <customfieldvalues>
                            <customfieldvalue>1|htads7:</customfieldvalue>

                        </customfieldvalues>
                    </customfield>
                                    </customfields>
    </item>
</channel>
</rss>