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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>[SERVER-41271] StringBuilder prints doubles with only 6 digits of precision, can lead to misleading log lines for plan ranking</title>
                <link>https://jira.mongodb.org/browse/SERVER-41271</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;We use &lt;tt&gt;StringBuilder&lt;/tt&gt; and &lt;tt&gt;str::stream&lt;/tt&gt; throughout the code base to produce log lines. When &lt;a href=&quot;https://github.com/mongodb/mongo/blob/713a1575150594222866b085c14bae4f13fe93b5/src/mongo/bson/util/builder.h#L385-L387&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;&lt;tt&gt;StringBuilder&lt;/tt&gt; prints a double&lt;/a&gt;, it passes through the &quot;%g&quot; format specifier to &lt;tt&gt;snprintf()&lt;/tt&gt;. The man pages for &lt;tt&gt;snprintf()&lt;/tt&gt; indicate that without an explicit precision, this prints the double with 6 digits of precision.&lt;/p&gt;

&lt;p&gt;This behavior may be acceptable for most uses of &lt;tt&gt;StringBuilder&lt;/tt&gt;, however, it leads to misleading log lines in the query subsystem. In particular, the &lt;tt&gt;PlanRanker&lt;/tt&gt; generates log lines which provide information about how the system is scoring candidate plans during the plan selection process. Consider the following set of log lines, provided by &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=christopher.harris&quot; class=&quot;user-hover&quot; rel=&quot;christopher.harris&quot;&gt;christopher.harris&lt;/a&gt;:&lt;/p&gt;

&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;&amp;nbsp;&lt;/pre&gt;
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						&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;2018-01-08T11:18:41.411+0530 D QUERY    [conn1] Scoring query plan: IXSCAN { _id: 1 } planHitEOF=0&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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				&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;2018-01-08T11:18:41.411+0530 D QUERY    [conn1] score(1) = baseScore(1) + productivity((0 advanced)/(3517483 works) = 0) + tieBreakers(2.84294e-08 noFetchBonus + 2.84294e-08 noSortBonus + 2.84294e-08 noIxisectBonus = 8.52883e-08)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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				&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;2018-01-08T11:18:41.411+0530 D QUERY    [conn1] score = 1 &lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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&lt;p/&gt;

&lt;p&gt;These log lines appear to suggest that the plan&apos;s score was 1, and that the tie-breakers were somehow discarded. However, the tie-breakers were not discarded. This is a symptom of the StringBuilder being unwilling to print more than 6 digits of precision. Unfortunately, this precision is important in query plan ranking due to our use of very small floating point numbers as tie-breakers.&lt;/p&gt;

&lt;p&gt;This may not be appropriate to fix in general for all log lines, but we can investigate producing a targeted fix to log plan scoring information with more precision.&lt;/p&gt;</description>
                <environment></environment>
        <key id="774671">SERVER-41271</key>
            <summary>StringBuilder prints doubles with only 6 digits of precision, can lead to misleading log lines for plan ranking</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="13201">Fixed</resolution>
                                        <assignee username="misha.ivkov@mongodb.com">Mikhail Ivkov</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                            <label>neweng</label>
                    </labels>
                <created>Wed, 22 May 2019 16:52:26 +0000</created>
                <updated>Sun, 29 Oct 2023 22:20:47 +0000</updated>
                            <resolved>Tue, 11 Jun 2019 21:14:53 +0000</resolved>
                                    <version>4.1.11</version>
                                    <fixVersion>4.3.1</fixVersion>
                                    <component>Diagnostics</component>
                    <component>Logging</component>
                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="2280359" author="xgen-internal-githook" created="Tue, 11 Jun 2019 21:13:01 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Misha Ivkov&apos;, &apos;email&apos;: &apos;misha.ivkov@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-41271&quot; title=&quot;StringBuilder prints doubles with only 6 digits of precision, can lead to misleading log lines for plan ranking&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-41271&quot;&gt;&lt;del&gt;SERVER-41271&lt;/del&gt;&lt;/a&gt; allow logging doubles with arbitrary precision&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/cad3a84e198e0851c7a8dd49d365ea1ce5cada50&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/cad3a84e198e0851c7a8dd49d365ea1ce5cada50&lt;/a&gt;&lt;/p&gt;</comment>
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