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<channel>
    <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-31679] Increase in disk i/o for writes to replica set</title>
                <link>https://jira.mongodb.org/browse/SERVER-31679</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Simple insert loop running against 1-node replica set&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;    db.c.insert({_id: 0, i: 0})&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 (i = 0; i &amp;lt; 100000; i++)&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.c.update({_id: 0}, {$inc: {i: 1}})&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;Shows a large increase in journal syncs, disk write requests, bytes written. 3.4.9 left, 3.6.0-rc0 right:&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/177525/177525_io.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt;&lt;/p&gt;

&lt;p&gt;It appears we&apos;re doing a flush on every update, even though there&apos;s no write concern.  In the simple repro above this doesn&apos;t seem to affect performance (for reasons tbd) but with more complex workloads the additional journal i/o will impact performance.&lt;/p&gt;

&lt;p&gt;Does not reproduce with standalone mongod.&lt;/p&gt;</description>
                <environment></environment>
        <key id="449479">SERVER-31679</key>
            <summary>Increase in disk i/o for writes to replica set</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="13201">Fixed</resolution>
                                        <assignee username="geert.bosch@mongodb.com">Geert Bosch</assignee>
                                    <reporter username="bruce.lucas@mongodb.com">Bruce Lucas</reporter>
                        <labels>
                            <label>SWNA</label>
                    </labels>
                <created>Mon, 23 Oct 2017 16:59:57 +0000</created>
                <updated>Mon, 30 Oct 2023 23:12:34 +0000</updated>
                            <resolved>Mon, 26 Feb 2018 21:30:06 +0000</resolved>
                                    <version>3.6.0-rc0</version>
                                    <fixVersion>3.6.6</fixVersion>
                    <fixVersion>3.7.3</fixVersion>
                                    <component>Replication</component>
                    <component>Storage</component>
                                        <votes>0</votes>
                                    <watches>22</watches>
                                                                                                                <comments>
                            <comment id="1898452" author="xgen-internal-githook" created="Tue, 22 May 2018 16:43:43 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;username&apos;: &apos;GeertBosch&apos;, &apos;name&apos;: &apos;Geert Bosch&apos;, &apos;email&apos;: &apos;geert@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-31679&quot; title=&quot;Increase in disk i/o for writes to replica set&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-31679&quot;&gt;&lt;del&gt;SERVER-31679&lt;/del&gt;&lt;/a&gt; Limit journaling frequency without oplog waiters&lt;/p&gt;

&lt;p&gt;(cherry picked from commit f23bcbfa6d08c24b5570b3b29641f96babfc6a34)&lt;br/&gt;
Branch: v3.6&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/a5656bc506fcdfe36d44cfb3c17969cbe35695c0&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/a5656bc506fcdfe36d44cfb3c17969cbe35695c0&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1816137" author="xgen-internal-githook" created="Mon, 26 Feb 2018 17:01:50 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;email&apos;: &apos;geert@mongodb.com&apos;, &apos;name&apos;: &apos;Geert Bosch&apos;, &apos;username&apos;: &apos;GeertBosch&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-31679&quot; title=&quot;Increase in disk i/o for writes to replica set&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-31679&quot;&gt;&lt;del&gt;SERVER-31679&lt;/del&gt;&lt;/a&gt; Limit journaling frequency without oplog waiters&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/f23bcbfa6d08c24b5570b3b29641f96babfc6a34&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/f23bcbfa6d08c24b5570b3b29641f96babfc6a34&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1792105" author="bruce.lucas@10gen.com" created="Thu, 1 Feb 2018 18:19:08 +0000"  >&lt;p&gt;Following up our discussion today, let&apos;s refocus this ticket on disk i/o due to log flushes, which is is a large effect and is in itself a problem for some customers, and leave aside for now issues about impact on throughput, which are more subtle and easily conflated with other 3.6 performance regressions.&lt;/p&gt;

&lt;p&gt;Here&apos;s a multi-threaded version of the simple update workload in the initial comment:&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;function repro {&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;    threads=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;&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 t in $(seq $threads); do    &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;        mongo --eval &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;            db.c.insert({_id: $t, i: 0})&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 (i = 0; i &amp;lt; 20000; i++) {&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;                db.c.update({_id: $t}, {\$inc: {i: 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;&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;
				&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;        &quot; &amp;amp;&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;    done&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;    wait&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;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;Here are four pairs of runs at 1, 2, 4, and 8 threads, against a 2-node repl set; the first run of each pair is 3.4, the second is 3.6:&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/177525/177525_io.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt;&lt;/p&gt;


&lt;ul&gt;
	&lt;li&gt;In the single-threaded case, 3.4 (A) does only a constant 30 flushes per second (which is too small to even see at the vertical scale of that chart), whereas 3.6 (B) appears to do one flush per update (i.e. thousands of flushes per second).&lt;/li&gt;
&lt;/ul&gt;


&lt;ul&gt;
	&lt;li&gt;As the number of threads increases, the disparity decreases, for this particular workload at least; above 8 threads (not shown above) there is rough parity.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;I would expect that if we can fix the single-threaded case in the sense of restoring 3.6 to the 3.4 behavior of 30 flushes per second  we will have fixed the other cases, and I think we can declare this ticket finished.&lt;/p&gt;</comment>
                            <comment id="1789685" author="bruce.lucas@10gen.com" created="Tue, 30 Jan 2018 20:23:12 +0000"  >&lt;p&gt;Note that there are two different workloads on this ticket, one single-threaded and one multi-threaded. I don&apos;t know if they are the same issue; if not we should split off the multi-threaded workload into a separate ticket.&lt;/p&gt;</comment>
                            <comment id="1788604" author="michael.cahill" created="Tue, 30 Jan 2018 05:03:50 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=sue.loverso&quot; class=&quot;user-hover&quot; rel=&quot;sue.loverso&quot;&gt;sue.loverso&lt;/a&gt;, can you please investigate, and in particular see whether the changes contemplated in &lt;a href=&quot;https://jira.mongodb.org/browse/WT-3531&quot; title=&quot;Provide a way to flush the log if commits were out of timestamp order&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-3531&quot;&gt;WT-3531&lt;/a&gt; help with &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=bruce.lucas&quot; class=&quot;user-hover&quot; rel=&quot;bruce.lucas&quot;&gt;bruce.lucas&lt;/a&gt;&apos;s workload can be made to sync the journal less?&lt;/p&gt;</comment>
                            <comment id="1707525" author="bruce.lucas@10gen.com" created="Tue, 24 Oct 2017 16:43:42 +0000"  >&lt;p&gt;It&apos;s difficult to separate out any impact of this issue from the impact of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-31694&quot; title=&quot;17% throughput regression in insert workload&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-31694&quot;&gt;&lt;del&gt;SERVER-31694&lt;/del&gt;&lt;/a&gt; and/or other performance regressions in 3.6.0-rc0, but here&apos;s an attempt.&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/169141/169141_four.png&quot; width=&quot;100%&quot; style=&quot;border: 0px solid black&quot; /&gt;&lt;/span&gt;&lt;/p&gt;

&lt;p&gt;First two runs are updates without write concern on 3.4.9 then 3.6.0-rc0, showing a performance regression.&lt;/p&gt;

&lt;p&gt;The second pair of runs are 3.4.9 vs 3.6.0-rc0 with a mix of ordinary and j:true updates:&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;        threads=20&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 t in $(seq $threads); do    &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;            @echo mongo --eval &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;                db.c.insert({_id: $t, i: 0})&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 (i = 0; i &amp;lt; 100000; i++) {&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
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			&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;
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			&lt;/td&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
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			&lt;/td&gt;
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			&lt;/td&gt;
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			&lt;/td&gt;
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			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;The second pair with j:true in the mix show a larger performance regression. I suspect that the incremental regression may be due to the impact of the additional syncs on the j:true operations.&lt;/p&gt;</comment>
                            <comment id="1706733" author="bruce.lucas@10gen.com" created="Mon, 23 Oct 2017 21:30:14 +0000"  >&lt;p&gt;I have a multi-threaded workload that includes some j:true ops and shows a decrease in performance. Will post details tomorrow. &lt;/p&gt;

&lt;p&gt;I think the large increase in i/o could in itself be a problem for some users. &lt;/p&gt;</comment>
                            <comment id="1706582" author="milkie" created="Mon, 23 Oct 2017 19:54:04 +0000"  >&lt;p&gt;This behavior is mostly likely due to &lt;a href=&quot;https://jira.mongodb.org/browse/WT-3531&quot; title=&quot;Provide a way to flush the log if commits were out of timestamp order&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-3531&quot;&gt;WT-3531&lt;/a&gt;; we left out an optimization that was in 3.4 because of the difficulty of keeping it in 3.6.&lt;br/&gt;
The optimization only applies to single-writer workloads, so I suspect more complex workloads would actually not be affected by this.  I also believe that the only significant result of this would be to increase latency of single-stream writer workloads that use a write concern with w:majority, since the optimization results in the ability to overlap the time waiting for journal on the primary with the time waiting for journal on secondaries (since the secondaries can see the oplog sooner; they don&apos;t have to wait for the journal flush).&lt;/p&gt;

&lt;p&gt;Bruce, I would not expect the simple insert loop here to actually complete slower than in 3.4, as the journal flushes are done in a separate thread from the writers, and we still group journal flushes.&lt;/p&gt;</comment>
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