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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-70041] POC: Optimise available ticket count based on time spent in WiredTiger</title>
                <link>https://jira.mongodb.org/browse/SERVER-70041</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;WiredTiger maintains several statistics that reflect on how long operations are taking inside the storage engine and if the application threads are waiting on page reads or write. We will experiment with adjusting the total available ticket count based on these statistics to optimize between the workload performance and the concurrency into the storage engine.&lt;/p&gt;

&lt;p&gt;The relevant statistics that I think could be helpful are the following:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Frequency distribution of the operation duration inside WiredTiger - available as a histogram&lt;/li&gt;
	&lt;li&gt;Frequency distribution of the disk latencies - available as a histogram&lt;/li&gt;
	&lt;li&gt;A count of threads waiting at any moment to read pages from the disk or write to the disk.&lt;/li&gt;
&lt;/ul&gt;
</description>
                <environment></environment>
        <key id="2146880">SERVER-70041</key>
            <summary>POC: Optimise available ticket count based on time spent in WiredTiger</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="sulabh.mahajan@mongodb.com">Sulabh Mahajan</assignee>
                                    <reporter username="sulabh.mahajan@mongodb.com">Sulabh Mahajan</reporter>
                        <labels>
                    </labels>
                <created>Wed, 28 Sep 2022 10:55:04 +0000</created>
                <updated>Fri, 14 Oct 2022 13:00:52 +0000</updated>
                            <resolved>Fri, 14 Oct 2022 13:00:52 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="4893401" author="sulabh.mahajan" created="Tue, 11 Oct 2022 08:48:12 +0000"  >&lt;p&gt;Update:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;Made code changes to trigger a periodic job whose purpose is to query the engine for the &quot;load&quot; and also &quot;recommendations&quot; to change the concurrency.&lt;/li&gt;
	&lt;li&gt;Added methods in the storage engine to support the above queries.&lt;/li&gt;
	&lt;li&gt;For WiredTiger, I am querying for perf histograms and the threads waiting on reads/writes. I have also added to histogram a total operation count.&lt;/li&gt;
	&lt;li&gt;I am still experimenting with the best means to derive a &quot;load score&quot; from the statistics.&lt;/li&gt;
	&lt;li&gt;An initial idea I am toying with is to have weighted buckets - the bucket with higher latency costs more, and the bucket with the least latency costs 0. Then derive a weighted cost of the latency compared to the overall throughput.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;I tried the above scheme with YCSB 60 - 100% reads with 128 and 16 threads separately. Here are how they compare from the perspective of the read load score:&lt;/p&gt;

&lt;p&gt;&lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/attachment/407501/407501_Screen+Shot+2022-10-11+at+10.40.55+am.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt; &lt;/p&gt;

&lt;p&gt;&lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/attachment/407502/407502_Screen+Shot+2022-10-11+at+10.41.05+am.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt; &lt;/p&gt;

&lt;p&gt;The pattern is very clear when seen between the two runs. Next, I want to try adjusting the read tickets in real time if the load score is above a certain value, for instance, 50 or even 10.&lt;/p&gt;

&lt;p&gt;The load patterns for the writes are not very clear. They benefit from higher concurrency, but I also realised that since the writes mostly go to the cache and hence the histogram buckets might not be sized correctly to capture a change in latency distribution.&lt;/p&gt;

&lt;p&gt;For instance, here is the load score for the writes with 128 and 16 tickets:&lt;/p&gt;

&lt;p&gt; &lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/attachment/407508/407508_Screen+Shot+2022-10-11+at+11.26.31+am.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt; &lt;br/&gt;
 &lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/attachment/407507/407507_Screen+Shot+2022-10-11+at+11.26.45+am.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt; &lt;/p&gt;

&lt;p&gt;Note the load score is being calculated as follows, with bucket 0 (operations faster than 100us) getting a 0 weight. It is effectively a score that summarizes the distribution of the latencies inside WiredTiger and is higher if the distribution shifts to have a larger tail in the collected histograms.&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;void WTLoadStats::calcLoads() {&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;    readLoad = ((opReadLatency100_249us * 2.5) + (opReadLatency250_499us * 5) +&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;                (opReadLatency500_999us * 10) + (opReadLatency1000_9999us * 100) +&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;                (opReadLatency10000us * 1000)) /&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;        (readThroughput + 1);&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;&amp;nbsp;&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;    writeLoad = ((opWriteLatency100_249us * 2.5) + (opWriteLatency250_499us * 5) +&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;                 (opWriteLatency500_999us * 10) + (opWriteLatency1000_9999us * 100) +&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;                 (opWriteLatency10000us * 1000)) /&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;        (writeThroughput + 1);&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;}&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
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&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;</comment>
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