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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>
    </build-info>


<item>
            <title>[DOCS-11656] Document convertShardKeyToHashed function</title>
                <link>https://jira.mongodb.org/browse/DOCS-11656</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description%3A&quot;&gt;&lt;/a&gt;Description: &lt;/h2&gt;

&lt;p&gt;This change added in a mongo shell function &quot;convertShardKeyToHashed&quot;. This function converts a bson key value pair into the hashed value that would be used for indexing/sharding.&lt;/p&gt;

&lt;p&gt;Example usage from &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/shell/shell_utils.cpp#L189&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;the source&lt;/a&gt;:&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: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;/**&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * This function computes a hash value for a document.&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * Specifically, this is the same hash function that is used to form a hashed index,&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * and thus used to generate shard keys for a collection.&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; *&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * e.g.&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; // For a given collection prepared like so:&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; use mydb&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; db.mycollection.createIndex({ x: &quot;hashed&quot; })&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; sh.shardCollection(&quot;mydb.mycollection&quot;, { x: &quot;hashed&quot; })&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; // And a sample object like so:&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; var obj = { x: &quot;Whatever key&quot;, y: 2, z: 10.0 }&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; // The hashed value of the shard key can be acquired from the shard key-value pair like so:&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;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; * &amp;gt; convertShardKeyToHashed({x: &quot;Whatever key&quot;})&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: #008200; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt; */&lt;/span&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;&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;h2&gt;&lt;a name=&quot;Scopeofchanges%3A&quot;&gt;&lt;/a&gt;Scope of changes: &lt;/h2&gt;

&lt;ul&gt;
	&lt;li&gt;4.0&lt;/li&gt;
	&lt;li&gt;new ref page and toc pages&lt;/li&gt;
	&lt;li&gt;add link to new page from hash index page&lt;/li&gt;
	&lt;li&gt;add link to new page from /core/hashed-sharding.txt&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;Not adding to general mentions about hashed sharding/hashed indexes; e.g.:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;indexes&lt;/li&gt;
	&lt;li&gt;sharding&lt;/li&gt;
	&lt;li&gt;move chunk &amp;#8211; since you would sh.status to get the bounds of the chunk to move&lt;/li&gt;
	&lt;li&gt;etc.&lt;/li&gt;
&lt;/ul&gt;


&lt;h2&gt;&lt;a name=&quot;Impacttootherdocsoutsideofthisproduct%3A&quot;&gt;&lt;/a&gt;Impact to other docs outside of this product: &lt;/h2&gt;

&lt;p&gt;none&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%3A&quot;&gt;&lt;/a&gt;MVP: &lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%3A&quot;&gt;&lt;/a&gt;Resources: &lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;EngineeringTicketDescription%3A&quot;&gt;&lt;/a&gt;Engineering Ticket Description:&lt;/h2&gt;

&lt;p&gt;Users may sometimes want to figure out the hashed value for a certain document&apos;s shard key field. For instance the reason for doing that might be to identify the shard key range / chunk the document belongs to (when a hashed shard key is used). There a ways to do that, namely:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;Run a query on the shard key and inspect the index key (the `$returnKey` query option)&lt;/li&gt;
	&lt;li&gt;Run a query on the shard key and inspect the index scan bounds in the $explain output&lt;/li&gt;
	&lt;li&gt;Re-start the server in test mode and use the &lt;tt&gt;_hashBSONElement&lt;/tt&gt; command&lt;/li&gt;
	&lt;li&gt;Port &lt;tt&gt;BSONElementHasher&lt;/tt&gt; into a custom application&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;All of these methods are pretty clumsy and inefficient when all you need is to get a hashed value for an arbitrary field. It would be much user-friendly if &lt;tt&gt;BSONElementHasher&lt;/tt&gt; could be run on the client side (i.e. in the &lt;tt&gt;mongo&lt;/tt&gt; shell) via a helper function. &lt;/p&gt;</description>
                <environment></environment>
        <key id="533943">DOCS-11656</key>
            <summary>Document convertShardKeyToHashed function</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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="13201">Fixed</resolution>
                                        <assignee username="kay.kim@mongodb.com">Kay Kim</assignee>
                                    <reporter username="kay.kim@mongodb.com">Kay Kim</reporter>
                        <labels>
                            <label>neweng</label>
                    </labels>
                <created>Wed, 25 Apr 2018 15:16:43 +0000</created>
                <updated>Sun, 29 Oct 2023 13:57:54 +0000</updated>
                            <resolved>Thu, 21 Jun 2018 21:22:07 +0000</resolved>
                                                    <fixVersion>3.7.6</fixVersion>
                                        <due></due>
                            <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="1928252" author="xgen-internal-githook" created="Thu, 21 Jun 2018 21:21:26 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;kay-kim&apos;, &apos;name&apos;: &apos;kay&apos;, &apos;email&apos;: &apos;kay.kim@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-11656&quot; title=&quot;Document convertShardKeyToHashed function&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-11656&quot;&gt;&lt;del&gt;DOCS-11656&lt;/del&gt;&lt;/a&gt;: convertShardKeyToHashed.txt&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/ed3e190efbefc8acd2b3f1568e2944fe2bb50e12&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/ed3e190efbefc8acd2b3f1568e2944fe2bb50e12&lt;/a&gt;&lt;/p&gt;</comment>
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