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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-4215] multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs </title>
                <link>https://jira.mongodb.org/browse/SERVER-4215</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;...think this has to do with migration triggered from the &lt;b&gt;same&lt;/b&gt; mongos, so version is auto-reloaded afterward.&lt;/p&gt;

&lt;p&gt;Sample bigMapReduce.js that fails - one of the connections has a stale version compared to the current version.&lt;/p&gt;</description>
                <environment></environment>
        <key id="24523">SERVER-4215</key>
            <summary>multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs </summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <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="9">Done</resolution>
                                        <assignee username="greg_10gen">Greg Studer</assignee>
                                    <reporter username="greg_10gen">Greg Studer</reporter>
                        <labels>
                    </labels>
                <created>Fri, 4 Nov 2011 17:53:46 +0000</created>
                <updated>Mon, 11 Jul 2016 18:32:46 +0000</updated>
                            <resolved>Wed, 18 Jan 2012 15:22:12 +0000</resolved>
                                    <version>2.1.0</version>
                                    <fixVersion>2.1.0</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="80718" author="greg_10gen" created="Wed, 18 Jan 2012 15:22:12 +0000"  >&lt;p&gt;Fixed, will continue refactoring in a new ticket.&lt;/p&gt;</comment>
                            <comment id="76668" author="greg_10gen" created="Thu, 29 Dec 2011 21:42:41 +0000"  >&lt;p&gt;Keeping lock for sharded m/r output, but the cursor method here should allow m/r to work with migrations on the input collection.  Added a new test of m/r with continuous migrations, can be tweaked in the future for sharded output as well.  &lt;/p&gt;</comment>
                            <comment id="76666" author="auto" created="Thu, 29 Dec 2011 21:41:39 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;gregstuder&apos;, u&apos;name&apos;: u&apos;gregs&apos;, u&apos;email&apos;: u&apos;greg@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt; use local cursor instead of dist lock for protection against migrate in m/r&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/009cc229ea0af766e632db87d5d6b45f7a60a275&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/009cc229ea0af766e632db87d5d6b45f7a60a275&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="76664" author="auto" created="Thu, 29 Dec 2011 21:41:36 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;gregstuder&apos;, u&apos;name&apos;: u&apos;gregs&apos;, u&apos;email&apos;: u&apos;greg@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt; check version and lock docs to server with cursor early in m/r&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/64b596993b18e5a22becf729549ec0386ce278a3&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/64b596993b18e5a22becf729549ec0386ce278a3&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="75723" author="greg_10gen" created="Fri, 23 Dec 2011 18:58:11 +0000"  >&lt;p&gt;Was looking at this yesterday (and a bit more today) - think one issue isn&apos;t the number of retries per-se but that we don&apos;t check the ns version until after all the prep work has been done (creating temporary collections) - fast migrations in the meantime can interfere and with a large number of shards almost always will.  &lt;/p&gt;

&lt;p&gt;In this case, I think we may just need to check the ns version right away, and potentially open a cursor to make sure the data we&apos;re mapReducing doesn&apos;t get deleted.  Long running ops in general are tricky.&lt;/p&gt;</comment>
                            <comment id="75551" author="auto" created="Thu, 22 Dec 2011 20:58:45 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;agirbal&apos;, u&apos;name&apos;: u&apos;agirbal&apos;, u&apos;email&apos;: u&apos;antoine@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt;: cannot retry enough times to satisfy tests, use lock&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/4691085ea565db1b52be8ab63332da94347f2fea&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/4691085ea565db1b52be8ab63332da94347f2fea&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="75215" author="auto" created="Wed, 21 Dec 2011 21:31:58 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;agirbal&apos;, u&apos;name&apos;: u&apos;agirbal&apos;, u&apos;email&apos;: u&apos;antoine@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt;: previous commit broke output of MR&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/4fa93b277db5613bdd11019d04c1cd0da1c1d162&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/4fa93b277db5613bdd11019d04c1cd0da1c1d162&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="74154" author="antoine" created="Sat, 17 Dec 2011 19:45:51 +0000"  >&lt;p&gt;seems like the current code does not retry enough.&lt;br/&gt;
bigMapReduce.js fails about 50% of time.&lt;br/&gt;
{&lt;br/&gt;
        &quot;errmsg&quot; : &quot;exception: could not run map command on all shards for ns test.foo and query {} :: caused by :: ns: test.foo too many retries of sta&lt;br/&gt;
le version info(send)&quot;,&lt;br/&gt;
        &quot;code&quot; : 13388,&lt;br/&gt;
        &quot;ok&quot; : 0&lt;br/&gt;
}&lt;/p&gt;</comment>
                            <comment id="73170" author="auto" created="Wed, 14 Dec 2011 21:28:09 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;gregstuder&apos;, u&apos;name&apos;: u&apos;Greg Studer&apos;, u&apos;email&apos;: u&apos;greg@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt; use pcursor for finalized reduce step&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/44ef35280f4d1112934e7f338007f95a0aeadae1&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/44ef35280f4d1112934e7f338007f95a0aeadae1&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="73136" author="auto" created="Wed, 14 Dec 2011 19:45:12 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;gregstuder&apos;, u&apos;name&apos;: u&apos;Greg Studer&apos;, u&apos;email&apos;: u&apos;greg@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-4215&quot; title=&quot;multiple connections to shards can rarely get mutually inconsistent versions when migrate occurs &quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-4215&quot;&gt;&lt;del&gt;SERVER-4215&lt;/del&gt;&lt;/a&gt; use consistent cursor for map phase&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/082a92b92097041174a5bd32a4dcd352b5ae3a00&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/082a92b92097041174a5bd32a4dcd352b5ae3a00&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="64790" author="greg_10gen" created="Fri, 4 Nov 2011 17:57:49 +0000"  >&lt;p&gt;Also, to clarify the attachment, the versionStale doesn&apos;t mean that a stale config exception was triggered, just that the sequence number of the current version of the namespace/shard is different from the sequence number of the chunkManager of the correctly executed command (the actual version number used is not available after it changes).  &lt;/p&gt;</comment>
                            <comment id="64787" author="greg_10gen" created="Fri, 4 Nov 2011 17:54:33 +0000"  >&lt;p&gt;may also apply for general parallel cursor case.&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="24592">SERVER-4220</issuekey>
        </issuelink>
                            </outwardlinks>
                                                        </issuelinktype>
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                <attachments>
                            <attachment id="13731" name="mr_output_that_fails.txt" size="1419316" author="greg_10gen" created="Fri, 4 Nov 2011 17:53:47 +0000"/>
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