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    <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-18885] Readahead startup warning is inconsistent with the documentation</title>
                <link>https://jira.mongodb.org/browse/SERVER-18885</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p/&gt;
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&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;
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					&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;2015-06-04T10:20:40.494-0400 [initandlisten] ** WARNING: Readahead for DBPATH is set to READAHEAD_VALUE&lt;/span&gt;&lt;/pre&gt;
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					&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;2015-06-04T10:20:40.494-0400 [initandlisten] **          We suggest setting it to 256KB (512 sectors) or less&lt;/span&gt;&lt;/pre&gt;
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					&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;2015-06-04T10:20:40.494-0400 [initandlisten] **          http://dochub.mongodb.org/core/readahead&lt;/span&gt;&lt;/pre&gt;
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&lt;p/&gt;

&lt;p&gt;&lt;a href=&quot;http://dochub.mongodb.org/core/readahead&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://dochub.mongodb.org/core/readahead&lt;/a&gt; links to &lt;a href=&quot;http://docs.mongodb.org/manual/administration/production-notes/#readahead&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://docs.mongodb.org/manual/administration/production-notes/#readahead&lt;/a&gt;, where we recommend:&lt;/p&gt;
&lt;blockquote&gt;
&lt;p&gt;Ensure that readahead settings for the block devices that store the database files are appropriate. For random access use patterns, set low readahead values. A readahead of 32 (16kb) often works well.&lt;br/&gt;
For a standard block device, you can run sudo blockdev --report to get the readahead settings and sudo blockdev --setra &amp;lt;value&amp;gt; &amp;lt;device&amp;gt; to change the readahead settings. Refer to your specific operating system manual for more information.&lt;/p&gt;&lt;/blockquote&gt;

&lt;p&gt;These 2 suggestions are inconsistent. We should just refer to the docs and keep our recommendation in one place.&lt;/p&gt;</description>
                <environment></environment>
        <key id="209326">SERVER-18885</key>
            <summary>Readahead startup warning is inconsistent with the documentation</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="gregory.wlodarek@mongodb.com">Gregory Wlodarek</assignee>
                                    <reporter username="joanna.cheng@mongodb.com">Joanna Cheng</reporter>
                        <labels>
                    </labels>
                <created>Tue, 9 Jun 2015 00:22:49 +0000</created>
                <updated>Thu, 11 Oct 2018 14:58:57 +0000</updated>
                            <resolved>Thu, 11 Oct 2018 14:58:57 +0000</resolved>
                                                                    <component>MMAPv1</component>
                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="2030140" author="gregory.wlodarek" created="Thu, 11 Oct 2018 14:58:57 +0000"  >&lt;p&gt;Marking this as gone away because if others need to use a non-standard read-ahead value (32kB), that&apos;s fine, we don&apos;t need to warn them.&lt;br/&gt;
&lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;img src=&quot;https://ssl.gstatic.com/ui/v1/icons/mail/images/cleardot.gif&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt;&lt;br/&gt;
We don&apos;t recommend read-ahead settings for WiredTiger since WiredTiger does its own selection of read sizes, typically determined by its pagesize, which wasn&apos;t the case for MMAP, we relied on implicit paging in by the OS.&lt;/p&gt;

&lt;p&gt;In regards to the inconsistency with the documentation, the documentation states that 32kB is a value that often works well, and MongoDB recommends a value of 256kB or&#160;&lt;b&gt;less&lt;/b&gt;. 256kB being the reason to let at least one read-ahead of one large document, since 256kB is the chunk-size of GridFS.&lt;/p&gt;</comment>
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            <issuekey id="52960">SERVER-7335</issuekey>
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