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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-20197] find() on collection with large documents slower on WiredTiger than MMAPv1</title>
                <link>https://jira.mongodb.org/browse/SERVER-20197</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Retrieval of large documents under MongoDB 3.0.6 and WiredTiger is significantly slower than 3.0.6 running MMAPv1.  With the following reproduction on my macbook, I saw the following execution times, running the find() operation twice to account for cold data:&lt;/p&gt;
&lt;div class=&apos;table-wrap&apos;&gt;
&lt;table class=&apos;confluenceTable&apos;&gt;&lt;tbody&gt;
&lt;tr&gt;
&lt;th class=&apos;confluenceTh&apos;&gt; Engine&lt;/th&gt;
&lt;th class=&apos;confluenceTh&apos;&gt; First find&lt;/th&gt;
&lt;th class=&apos;confluenceTh&apos;&gt; Second find&lt;/th&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td class=&apos;confluenceTd&apos;&gt;MMAPv1&lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; 312ms &lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; 1ms&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td class=&apos;confluenceTd&apos;&gt;WiredTiger&lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; 8140ms&lt;/td&gt;
&lt;td class=&apos;confluenceTd&apos;&gt; 668ms&lt;/td&gt;
&lt;/tr&gt;
&lt;/tbody&gt;&lt;/table&gt;
&lt;/div&gt;
</description>
                <environment></environment>
        <key id="227649">SERVER-20197</key>
            <summary>find() on collection with large documents slower on WiredTiger than MMAPv1</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="mathias@mongodb.com">Mathias Stearn</assignee>
                                    <reporter username="james.wahlin@mongodb.com">James Wahlin</reporter>
                        <labels>
                    </labels>
                <created>Sat, 29 Aug 2015 14:15:41 +0000</created>
                <updated>Mon, 21 Sep 2015 23:21:22 +0000</updated>
                            <resolved>Mon, 21 Sep 2015 23:21:22 +0000</resolved>
                                    <version>3.0.6</version>
                                                    <component>WiredTiger</component>
                                        <votes>0</votes>
                                    <watches>13</watches>
                                                                                                                <comments>
                            <comment id="1039106" author="redbeard0531" created="Mon, 21 Sep 2015 23:21:22 +0000"  >&lt;p&gt;Closing as Gone Away as the &quot;second find&quot; problem has been resolved by the combination of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18902&quot; title=&quot;Retrieval of documents larger that 1MB slower on WiredTiger than MMAPv1&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18902&quot;&gt;&lt;del&gt;SERVER-18902&lt;/del&gt;&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-16444&quot; title=&quot;Avoid copying data out of WT buffers during tables scans&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-16444&quot;&gt;&lt;del&gt;SERVER-16444&lt;/del&gt;&lt;/a&gt;. They make cached reads as fast in wiredtiger as they were in mmapv1.&lt;/p&gt;

&lt;p&gt;The &quot;first read&quot; issue is due to internal design differences that allow for features like compression and checksumming. Reading uncached data in wiredtiger requires processing the data to make it useable.&lt;/p&gt;</comment>
                    </comments>
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                            <issuelinktype id="10012">
                    <name>Related</name>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="209584">SERVER-18902</issuekey>
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            <issuelink>
            <issuekey id="173056">SERVER-16444</issuekey>
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                            <customfieldvalue>&lt;p&gt;1) Setup a 2 member MongoDB 3.0.6 replica set with:&lt;/p&gt;
&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;One member running WiredTiger&lt;/li&gt;
	&lt;li&gt;One member running MMAPv1&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;2) Load a data set with large documents:&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;use test;&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: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;var hugeString=&quot;&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: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;for (var i = 0; i &amp;lt; (1024 * 1100); i++) { hugeString = hugeString + &quot;12345&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: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;for (var j = 0; j &amp;lt; 1000; ++j) { db.test.insert({a: hugeString}); }&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;3) Run the following explain 2 times against both the WiredTiger and the MMAPv1 members:&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;use test;&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;db.test.find().explain(verbose=&apos;executionStats&apos;);&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
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