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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>[DOCS-7880] Comment on: &quot;manual/core/sharding-introduction.txt&quot;</title>
                <link>https://jira.mongodb.org/browse/DOCS-7880</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;p&gt;If  the mongoDB has the balancer that can migrating the chunks in shards to maintaing the data balance.why you say &quot;range based partitioning can result in an uneven distribution of data, which may negate some of the benefits of sharding. For example, if the shard key is a linearly increasing field, such as time, then all requests for a given time range will map to the same chunk, and thus the same shard.&quot;&lt;/p&gt;
</description>
                <environment>mongodb 3.2&lt;br/&gt;
&lt;br/&gt;
*Location*: &lt;a href=&quot;https://docs.mongodb.com/manual/core/sharding-introduction/&quot;&gt;https://docs.mongodb.com/manual/core/sharding-introduction/&lt;/a&gt;&lt;br/&gt;
*User-Agent*: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.122 Safari/537.36 SE 2.X MetaSr 1.0&lt;br/&gt;
*Referrer*: &lt;a href=&quot;https://docs.mongodb.com/?_ga=1.255109824.958390077.1461633920&quot;&gt;https://docs.mongodb.com/?_ga=1.255109824.958390077.1461633920&lt;/a&gt;&lt;br/&gt;
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        <key id="286735">DOCS-7880</key>
            <summary>Comment on: &quot;manual/core/sharding-introduction.txt&quot;</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="ravind.kumar">Ravind Kumar</assignee>
                                    <reporter username="xgen-internal-docs">Docs Collector User</reporter>
                        <labels>
                            <label>collector-298ba4e7</label>
                    </labels>
                <created>Mon, 16 May 2016 02:18:59 +0000</created>
                <updated>Fri, 3 Nov 2017 11:10:20 +0000</updated>
                            <resolved>Fri, 20 May 2016 13:32:20 +0000</resolved>
                                                    <fixVersion>01112017-cleanup</fixVersion>
                                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                <comments>
                            <comment id="1264575" author="ravind.kumar" created="Mon, 16 May 2016 10:56:32 +0000"  >&lt;p&gt;Hello Huang,&lt;/p&gt;

&lt;p&gt;We&apos;re working on revising these pages to make distinctions like this clearer. Until then, I hope the following explanation helps:&lt;/p&gt;

&lt;p&gt;With ranged-based partitioning, each chunk represents a range of shard key values with an inclusive lower and exclusive upper bound.&lt;/p&gt;

&lt;p&gt;For example:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;    chunkA : { lowerBound : 1, upperBound : 10 },&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;    chunkB : { lowerBound: 10, upperBound: 20 }&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;With this, the balancer would route new documents with a shard key value of 1 - 9 to chunk A, and 10 - 19 to chunk B.&lt;/p&gt;

&lt;p&gt;The reason for the warning is due to two special chunk ranges - minKey and maxKey. In order to ensure data is always stored on at least one chunk, there is a chunk that is given a lower bound of minKey, and a chunk given an upper bound of maxKey.&lt;/p&gt;

&lt;p&gt;minKey always compares as less than any other possible value. maxKey always compares as greater than any possible value.&lt;/p&gt;

&lt;p&gt;So, using the previous example:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;    chunkA : { lowerBound : minKey, upperBound : 10 },&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;    chunkB : { lowerBound: 10, upperBound: maxKey }&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;Now, if I have a key with value -1, -100, or -10000, that document would route to chunkA. If I have a key with 11, 110, and 11000, that document would go to chunkB.&lt;/p&gt;

&lt;p&gt;With monotonically increasing shard keys - or any shard key where the value is always increasing at a fixed rate - all new documents are routed to the chunk with maxKey as the upper bound. If there is a chunk split, one of the new chunks now contain the maxKey upper limit.&lt;/p&gt;

&lt;p&gt;So if I have a shard key that increases, such as a timestamp, all of my new data always ends up in a single chunk. The shard containing that chunk now receives all write operations, creating a bottleneck.&lt;/p&gt;

&lt;p&gt;It goes both ways - if I have a shard key that is always decreasing at a fixed rate, those documents are routed to the chunk with minKey as the lower bound, and the same bottleneck occurs.&lt;/p&gt;

&lt;p&gt;I hope this answers your question - please keep an eye on our documentation in the future, as we are planning updates to clarify many points on sharding.&lt;/p&gt;</comment>
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