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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-9158] WiredTiger readahead values</title>
                <link>https://jira.mongodb.org/browse/DOCS-9158</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;p&gt;The current &lt;a href=&quot;https://docs.mongodb.com/manual/administration/production-notes/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;production notes&lt;/a&gt; and &lt;a href=&quot;https://docs.mongodb.com/manual/administration/production-checklist-operations/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;operations checklist&lt;/a&gt; need to have the advice regarding readahead tuning amended for the WiredTiger use case.&lt;/p&gt;

&lt;p&gt;The new value for WT readahead is 0kb (zero), regardless of media type (spinning disk or SSD), and applies to both the $dbpath and journal directories.&lt;/p&gt;</description>
                <environment>Linux</environment>
        <key id="324425">DOCS-9158</key>
            <summary>WiredTiger readahead values</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="luke.prochazka@mongodb.com">Luke Prochazka</reporter>
                        <labels>
                            <label>bite-sized</label>
                    </labels>
                <created>Tue, 18 Oct 2016 06:01:35 +0000</created>
                <updated>Mon, 30 Oct 2023 21:23:19 +0000</updated>
                            <resolved>Fri, 27 Jan 2017 11:02:20 +0000</resolved>
                                                    <fixVersion>Server_Docs_20231030</fixVersion>
                                    <component>manual</component>
                        <due></due>
                            <votes>1</votes>
                                    <watches>15</watches>
                                                                                                                <comments>
                            <comment id="1487823" author="xgen-internal-githook" created="Mon, 30 Jan 2017 03:52:01 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;rkumar-mongo&apos;, u&apos;name&apos;: u&apos;ravind&apos;, u&apos;email&apos;: u&apos;ravind.kumar@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-9158&quot; title=&quot;WiredTiger readahead values&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-9158&quot;&gt;&lt;del&gt;DOCS-9158&lt;/del&gt;&lt;/a&gt;: set readahead to 0 for WiredTiger&lt;/p&gt;

&lt;p&gt;Signed-off-by: kay &amp;lt;kay.kim@10gen.com&amp;gt;&lt;br/&gt;
Branch: v3.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/2a7f255a232d7cd688a53154bdc5c0bd6893d74d&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/2a7f255a232d7cd688a53154bdc5c0bd6893d74d&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1487822" author="xgen-internal-githook" created="Mon, 30 Jan 2017 03:51:02 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;rkumar-mongo&apos;, u&apos;name&apos;: u&apos;ravind&apos;, u&apos;email&apos;: u&apos;ravind.kumar@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/DOCS-9158&quot; title=&quot;WiredTiger readahead values&quot; class=&quot;issue-link&quot; data-issue-key=&quot;DOCS-9158&quot;&gt;&lt;del&gt;DOCS-9158&lt;/del&gt;&lt;/a&gt;: set readahead to 0 for WiredTiger&lt;/p&gt;

&lt;p&gt;Signed-off-by: kay &amp;lt;kay.kim@10gen.com&amp;gt;&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/a62e75c977aa84727a9bec0fc0e7f71612d015fd&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/a62e75c977aa84727a9bec0fc0e7f71612d015fd&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1486636" author="ravind.kumar" created="Fri, 27 Jan 2017 11:02:20 +0000"  >&lt;p&gt;&lt;a href=&quot;https://github.com/mongodb/docs/pull/2831&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/pull/2831&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1486596" author="eoin.brazil" created="Fri, 27 Jan 2017 09:36:29 +0000"  >&lt;p&gt;LGTM to me as well. Thanks!&lt;/p&gt;</comment>
                            <comment id="1484451" author="luke.prochazka" created="Tue, 24 Jan 2017 22:46:43 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=ravind.kumar&quot; class=&quot;user-hover&quot; rel=&quot;ravind.kumar&quot;&gt;ravind.kumar&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;As a generalisation yes, the prefered value is zero, and it applies to &lt;b&gt;all&lt;/b&gt; WiredTiger versions.  There are always exceptions to the rule though, for instance on platforms that do not support the &lt;tt&gt;fadvise()&lt;/tt&gt; syscall (such as Windows), then FS cache pollution will be a factor.&lt;/p&gt;

&lt;p&gt;That said, I&apos;m not entirely sure how to word these exceptions.  Perhaps something like:&lt;/p&gt;

&lt;p&gt;&quot;The recommended readahead value for use with the WiredTiger storage engine is 0kb (zero).  On supported platforms, WiredTiger utilises the &lt;tt&gt;fadvise()&lt;/tt&gt; syscall to override the Operating System&apos;s readahead behaviour and to bypass the filesystem cache.  On platforms where &lt;tt&gt;fadvise()&lt;/tt&gt; is not supported (such as Windows), a readahead value of 16 (8kb) has been found to be suitable in some scenarios.&lt;/p&gt;

&lt;p&gt;These recommendations apply regardless of media type (magnetic or SSD), and applies to both the &lt;tt&gt;$dbpath&lt;/tt&gt; and journal directories.&quot;&lt;/p&gt;

&lt;p&gt;thanks&lt;br/&gt;
-Luke&lt;/p&gt;</comment>
                            <comment id="1483748" author="ravind.kumar" created="Tue, 24 Jan 2017 14:36:25 +0000"  >&lt;p&gt;Hi all,&lt;/p&gt;

&lt;p&gt;I&apos;ll be taking ownership of this change. &lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=luke.prochazka&quot; class=&quot;user-hover&quot; rel=&quot;luke.prochazka&quot;&gt;luke.prochazka&lt;/a&gt; one thing to confirm - is this generally universal for WT, or are there versions of MongoDB where the 0 setting may not be best?&lt;/p&gt;</comment>
                            <comment id="1483633" author="eoin.brazil" created="Tue, 24 Jan 2017 10:36:08 +0000"  >&lt;p&gt;Hi &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=allison.moore%40mongodb.com&quot; class=&quot;user-hover&quot; rel=&quot;allison.moore@mongodb.com&quot;&gt;allison.moore@mongodb.com&lt;/a&gt;,&lt;/p&gt;

&lt;p&gt;Is there an outstanding code review you need our input for as I&apos;d like to do whatever I can to help get this published?&lt;/p&gt;

&lt;p&gt;Thanks!&lt;br/&gt;
Eoin&lt;/p&gt;</comment>
                            <comment id="1482494" author="alexander.marquardt" created="Mon, 23 Jan 2017 13:39:58 +0000"  >&lt;p&gt;Is this going to be updated in the documentation? I find it more comfortable to make recommendations to the customer when the documentation reflects what I am recommending to them. &lt;/p&gt;

&lt;p&gt;CC: &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=braz&quot; class=&quot;user-hover&quot; rel=&quot;braz&quot;&gt;braz&lt;/a&gt;&lt;/p&gt;</comment>
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