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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-14506] special top chunk logic can move max chunk to a shard with incompatible tag</title>
                <link>https://jira.mongodb.org/browse/SERVER-14506</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;div class=&quot;panel&quot; style=&quot;background-color: #EEEEEE;border-color: #ccc;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;border-bottom-color: #ccc;background-color: #6CB33F;&quot;&gt;&lt;b&gt;Issue Status as of Aug 08, 2014&lt;/b&gt;&lt;/div&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #EEEEEE;&quot;&gt;
&lt;p&gt;&lt;b&gt;ISSUE SUMMARY&lt;/b&gt;&lt;br/&gt;
On &lt;a href=&quot;http://docs.mongodb.org/manual/core/tag-aware-sharding/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;tag-aware sharded clusters&lt;/a&gt;, when the balancer is active and the top/bottom chunk needs to be split, the new chunk may be temporarily moved to a shard with an incompatible tag thus temporarily violating tagging. &lt;/p&gt;

&lt;p&gt;This issue does not apply to sharded clusters using &lt;a href=&quot;http://docs.mongodb.org/manual/core/sharding-shard-key/#hashed-shard-keys&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;hashed shard keys&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;USER IMPACT&lt;/b&gt;&lt;br/&gt;
Users with a heavy insert load may experience poor performance due to unneccessary migrations.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;WORKAROUNDS&lt;/b&gt;&lt;br/&gt;
Users may consider adding a split point at an extremely high, unreachable shard key to prevent this behavior.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;AFFECTED VERSIONS&lt;/b&gt;&lt;br/&gt;
MongoDB production releases up to 2.6.5 are affected by this issue.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;FIX VERSION&lt;/b&gt;&lt;br/&gt;
The fix is included in the 2.6.6 production release.&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h6&gt;&lt;a name=&quot;Originaldescription&quot;&gt;&lt;/a&gt;Original description&lt;/h6&gt;

&lt;p&gt;In special logic for splitting top or bottom chunk &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/s/d_split.cpp#L886&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/s/d_split.cpp#L886&lt;/a&gt; sets shouldMigrate to true.&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/s/chunk.cpp#L466&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/s/chunk.cpp#L466&lt;/a&gt; goes along with the idea as long as balancing isn&apos;t disabled, and uses Shard::pick() to find the new target shard for the &quot;hot&quot; chunk.&lt;/p&gt;

&lt;p&gt;However, &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/s/shard.cpp#L425&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/s/shard.cpp#L425&lt;/a&gt; does not seem to take tags into account and ends up moving the chunk to a shard from which it must then immediately be moved in the next round (violating tagging in the meanwhile).&lt;/p&gt;

&lt;p&gt;This problem does not apply to hashed shard key since special logic is bypassed in that case.&lt;/p&gt;</description>
                <environment></environment>
        <key id="146111">SERVER-14506</key>
            <summary>special top chunk logic can move max chunk to a shard with incompatible tag</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="randolph@mongodb.com">Randolph Tan</assignee>
                                    <reporter username="asya.kamsky@mongodb.com">Asya Kamsky</reporter>
                        <labels>
                    </labels>
                <created>Wed, 9 Jul 2014 00:08:43 +0000</created>
                <updated>Tue, 12 May 2015 15:37:06 +0000</updated>
                            <resolved>Fri, 8 Aug 2014 14:20:10 +0000</resolved>
                                                    <fixVersion>2.6.6</fixVersion>
                    <fixVersion>2.7.5</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>8</watches>
                                                                                                                <comments>
                            <comment id="772868" author="xgen-internal-githook" created="Tue, 25 Nov 2014 22:27:36 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;renctan&apos;, u&apos;name&apos;: u&apos;Randolph Tan&apos;, u&apos;email&apos;: u&apos;randolph@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-14506&quot; title=&quot;special top chunk logic can move max chunk to a shard with incompatible tag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-14506&quot;&gt;&lt;del&gt;SERVER-14506&lt;/del&gt;&lt;/a&gt; special top chunk logic can move max chunk to a shard with incompatible tag&lt;/p&gt;

&lt;p&gt;Fix test&lt;br/&gt;
Branch: v2.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/d0cd0e0b62a85fb47b8be39e945715438410efec&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/d0cd0e0b62a85fb47b8be39e945715438410efec&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="772867" author="xgen-internal-githook" created="Tue, 25 Nov 2014 22:27:35 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;renctan&apos;, u&apos;name&apos;: u&apos;Randolph Tan&apos;, u&apos;email&apos;: u&apos;randolph@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-14506&quot; title=&quot;special top chunk logic can move max chunk to a shard with incompatible tag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-14506&quot;&gt;&lt;del&gt;SERVER-14506&lt;/del&gt;&lt;/a&gt; special top chunk logic can move max chunk to a shard with incompatible tag&lt;br/&gt;
(cherry picked from commit 9d1e5f95a2739a7672b697deb7d1da04ca8c4117)&lt;/p&gt;

&lt;p&gt;Conflicts:&lt;br/&gt;
	jstests/sharding/top_chunk_autosplit.js&lt;br/&gt;
	src/mongo/SConscript&lt;br/&gt;
	src/mongo/s/balance.cpp&lt;br/&gt;
	src/mongo/s/balancer_policy.cpp&lt;br/&gt;
	src/mongo/s/chunk.cpp&lt;br/&gt;
	src/mongo/s/d_split.cpp&lt;br/&gt;
Branch: v2.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/fd8a2779971d095b2d13fb4c2dd06a11118908a4&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/fd8a2779971d095b2d13fb4c2dd06a11118908a4&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="772866" author="xgen-internal-githook" created="Tue, 25 Nov 2014 22:27:33 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;renctan&apos;, u&apos;name&apos;: u&apos;Randolph Tan&apos;, u&apos;email&apos;: u&apos;randolph@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-14506&quot; title=&quot;special top chunk logic can move max chunk to a shard with incompatible tag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-14506&quot;&gt;&lt;del&gt;SERVER-14506&lt;/del&gt;&lt;/a&gt; special top chunk logic can move max chunk to a shard with incompatible tag&lt;/p&gt;

&lt;p&gt;Make DistributionStatus store ChunkTypes instead of BSONObj&lt;br/&gt;
(cherry picked from commit c30b981260e26dfeff315b766e2887d4f7404f89)&lt;/p&gt;

&lt;p&gt;Conflicts:&lt;br/&gt;
	src/mongo/s/balancer_policy.h&lt;br/&gt;
Branch: v2.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/a12f25486ecd7888e90950423e249a273d36aed8&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/a12f25486ecd7888e90950423e249a273d36aed8&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="684446" author="xgen-internal-githook" created="Fri, 8 Aug 2014 00:02:59 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;renctan&apos;, u&apos;name&apos;: u&apos;Randolph Tan&apos;, u&apos;email&apos;: u&apos;randolph@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-14506&quot; title=&quot;special top chunk logic can move max chunk to a shard with incompatible tag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-14506&quot;&gt;&lt;del&gt;SERVER-14506&lt;/del&gt;&lt;/a&gt; special top chunk logic can move max chunk to a shard with incompatible tag&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/9d1e5f95a2739a7672b697deb7d1da04ca8c4117&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/9d1e5f95a2739a7672b697deb7d1da04ca8c4117&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="684445" author="xgen-internal-githook" created="Fri, 8 Aug 2014 00:02:57 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;renctan&apos;, u&apos;name&apos;: u&apos;Randolph Tan&apos;, u&apos;email&apos;: u&apos;randolph@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-14506&quot; title=&quot;special top chunk logic can move max chunk to a shard with incompatible tag&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-14506&quot;&gt;&lt;del&gt;SERVER-14506&lt;/del&gt;&lt;/a&gt; special top chunk logic can move max chunk to a shard with incompatible tag&lt;/p&gt;

&lt;p&gt;Make DistributionStatus store ChunkTypes instead of BSONObj&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/c30b981260e26dfeff315b766e2887d4f7404f89&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/c30b981260e26dfeff315b766e2887d4f7404f89&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="653201" author="greg_10gen" created="Wed, 9 Jul 2014 16:00:16 +0000"  >&lt;p&gt;A workaround might be to add a split point at an extremely high, unreachable shard key value to prevent the top chunk optimization from coming into effect?&lt;/p&gt;</comment>
                    </comments>
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                    <name>Depends</name>
                                            <outwardlinks description="depends on">
                                        <issuelink>
            <issuekey id="148696">SERVER-14667</issuekey>
        </issuelink>
                            </outwardlinks>
                                                                <inwardlinks description="is depended on by">
                                                        </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10010">
                    <name>Duplicate</name>
                                                                <inwardlinks description="is duplicated by">
                                        <issuelink>
            <issuekey id="28358">SERVER-4687</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="202703">SERVER-18361</issuekey>
        </issuelink>
                            </outwardlinks>
                                                        </issuelinktype>
                            <issuelinktype id="10220">
                    <name>Tested</name>
                                            <outwardlinks description="tested by">
                                        <issuelink>
            <issuekey id="165876">SERVER-15831</issuekey>
        </issuelink>
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