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    <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>
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<item>
            <title>[SERVER-7831] m/r: reduce post processing: reduce lock time with &quot;nonAtomic&quot; option</title>
                <link>https://jira.mongodb.org/browse/SERVER-7831</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Merge too many documents, can take a long period of time,&lt;br/&gt;
and all of this time there is a global lock, we can avoid this,&lt;br/&gt;
with &quot;&lt;/p&gt;
{nonAtomic: true}
&lt;p&gt;&quot; option.&lt;/p&gt;

&lt;p&gt;This patch do this.&lt;/p&gt;</description>
                <environment></environment>
        <key id="58249">SERVER-7831</key>
            <summary>m/r: reduce post processing: reduce lock time with &quot;nonAtomic&quot; option</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="azat">Azat Khuzhin</reporter>
                        <labels>
                            <label>pull-request</label>
                    </labels>
                <created>Tue, 4 Dec 2012 07:59:32 +0000</created>
                <updated>Tue, 6 Dec 2022 05:27:01 +0000</updated>
                                                                            <component>MapReduce</component>
                                        <votes>3</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="655158" author="benety.goh" created="Thu, 10 Jul 2014 19:31:51 +0000"  >&lt;p&gt;Attached file containing pull request changes rebased on 81ed23939d7b94a14371241db247a76e85f050fe&lt;/p&gt;</comment>
                            <comment id="655153" author="benety.goh" created="Thu, 10 Jul 2014 19:26:03 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-13522&quot; title=&quot;Cleanup encapsulation violations and unused code&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-13522&quot;&gt;&lt;del&gt;SERVER-13522&lt;/del&gt;&lt;/a&gt; referred to the &quot;replace&quot; action while this one&apos;s about &quot;reduce&quot;.&lt;/p&gt;</comment>
                            <comment id="354965" author="bmiller@bloomenergy.com" created="Fri, 7 Jun 2013 00:23:23 +0000"  >&lt;p&gt;We think we&apos;ve been affected by this issue, and just wanted to comment on how this effects performance.&lt;/p&gt;

&lt;p&gt;When the server enters the &quot;M/R Reduce Post Processing&quot; stage, the global lock will shoot to 100%, rendering the primary almost completely useless &amp;#8211; queries time out, replica secondaries will fall behind, and the insert rate will drop dramatically.&lt;/p&gt;

&lt;p&gt;This more or less makes the out: &lt;/p&gt;
{reduce: &quot;collName&quot;}
&lt;p&gt; map reduce option impractical to use in a production environment.&lt;/p&gt;

&lt;p&gt;I asked about this on the mongodb-users group not too long ago. If it provides any useful background information, the post can be found &lt;a href=&quot;https://groups.google.com/forum/?fromgroups=#!topic/mongodb-user/eMlDDCKX7UY&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;</comment>
                            <comment id="285740" author="azat" created="Sun, 10 Mar 2013 18:41:52 +0000"  >&lt;p&gt;Any news?&lt;/p&gt;</comment>
                            <comment id="205953" author="azat" created="Tue, 4 Dec 2012 08:02:41 +0000"  >&lt;p&gt;Pull request - &lt;a href=&quot;https://github.com/mongodb/mongo/pull/333&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/pull/333&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
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                    <name>Duplicate</name>
                                                                <inwardlinks description="is duplicated by">
                                        <issuelink>
            <issuekey id="133409">SERVER-13748</issuekey>
        </issuelink>
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                                    </issuelinktype>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="130553">SERVER-13552</issuekey>
        </issuelink>
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                <attachments>
                            <attachment id="51887" name="pr333_rebase_353dccc.diff" size="3217" author="benety.goh@mongodb.com" created="Wed, 10 Sep 2014 16:13:38 +0000"/>
                            <attachment id="47431" name="pr333_rebase_81ed239.diff" size="3827" author="benety.goh@mongodb.com" created="Thu, 10 Jul 2014 19:31:51 +0000"/>
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