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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-5831] server stops processing requests during periodic flush</title>
                <link>https://jira.mongodb.org/browse/SERVER-5831</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;client is inserting records as quickly as it can. &lt;br/&gt;
seeing the insert rate drop to zero while background flushes happen. &lt;br/&gt;
have tested on 2.0.4 and 2.1.1 and see same behavior. &lt;/p&gt;

&lt;p&gt;mongostat output: &lt;br/&gt;
...&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;insert  query update delete getmore command flushes mapped  vsize    res locked % idx miss %     qr|qw   ar|aw  netIn netOut  conn       time &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; 23300      0      0      0       0       1       0   1.8g  6.01g   872m     93.7          0       0|0     0|1    12m     1k     2   15:59:24 &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; 22900      0      0      0       0       1       0   1.8g  6.01g   883m      105          0       0|0     0|1    12m     1k     2   15:59:25 &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; 23900      0      0      0       0       1       0   1.8g  6.01g   896m     98.7          0       0|0     0|1    12m     1k     2   15:59:26 &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; 22100      0      0      0       0       1       0   1.8g  6.01g   910m     96.4          0       0|0     0|1    11m     1k     2   15:59:27 &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; 18900      0      0      0       0       1       0   1.8g  6.01g   920m     95.7          0       0|0     0|1    10m     1k     2   15:59:28 &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; 16300      0      0      0       0       1       0   1.8g  6.01g   928m      106          0       0|0     0|0     8m     1k     2   15:59:29 &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; 17400      0      0      0       0       1       0   1.8g  6.01g   937m     99.2          0       0|0     0|1     9m     1k     2   15:59:30 &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;  9500      0      0      0       0       1       0   1.8g  6.01g   944m     52.6          0       0|0     0|1     5m     1k     2   15:59:31 &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;     0      0      0      0       0       1       0   1.8g  6.01g   944m        0          0       1|1     0|1    62b     1k     2   15:59:32 &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;     0      0      0      0       0       1       0   1.8g  6.01g   944m        0          0       1|1     0|1    62b     1k     2   15:59:33 &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;insert  query update delete getmore command flushes mapped  vsize    res locked % idx miss %     qr|qw   ar|aw  netIn netOut  conn       time &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; 11600      0      0      0       0       1       1   2.8g  8.01g   949m      345          0       0|0     0|1     6m     1k     2   15:59:34 &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;  9300      0      0      0       0       1       0   2.8g  8.01g   956m     95.4          0       0|0     0|1     4m     1k     2   15:59:35 &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;You can see that during the few seconds before the flush happens, inserts drop to zero. &lt;/p&gt;

&lt;p&gt;then about a minute later we see it again &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;16200      0      0      0       0       1       0   2.8g  8.01g  1.25g     93.1          0       0|0     0|1     8m     1k     2   16:00:24 &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; 16200      0      0      0       0       1       0   2.8g  8.01g  1.25g     95.3          0       0|0     0|1     8m     1k     2   16:00:25 &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; 17900      0      0      0       0       1       0   2.8g  8.01g  1.26g      109          0       0|0     0|1     9m     1k     2   16:00:26 &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; 17200      0      0      0       0       1       0   2.8g  8.01g  1.27g     96.9          0       0|0     0|1     9m     1k     2   16:00:27 &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;  8100      0      0      0       0       1       0   2.8g  8.01g  1.28g     60.6          0       0|0     0|1     4m     1k     2   16:00:28 &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;     0      0      0      0       0       1       0   2.8g  8.01g  1.28g        0          0       0|1     0|1    62b     1k     2   16:00:29 &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;  2700      0      0      0       0       1       1   2.8g  8.01g  1.28g      235          0       0|0     0|1     1m     1k     2   16:00:30 &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; 16200      0      0      0       0       1       0   2.8g  8.01g  1.29g     91.5          0       0|0     0|1     8m     1k     2   16:00:31 &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; 18900      0      0      0       0       1       0   2.8g  8.01g   1.3g      108          0       0|0     0|1    10m     1k     2   16:00:32 &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;I&apos;ve attached the test program that recreates this. &lt;/p&gt;</description>
                <environment>multiple. have run on my mac and on aws. </environment>
        <key id="38521">SERVER-5831</key>
            <summary>server stops processing requests during periodic flush</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="3">Duplicate</resolution>
                                        <assignee username="schwerin@mongodb.com">Andy Schwerin</assignee>
                                    <reporter username="jsr">Jared Rosoff</reporter>
                        <labels>
                            <label>performance</label>
                    </labels>
                <created>Sat, 12 May 2012 00:26:03 +0000</created>
                <updated>Wed, 10 Dec 2014 23:06:45 +0000</updated>
                            <resolved>Fri, 22 Nov 2013 21:27:25 +0000</resolved>
                                    <version>2.0.4</version>
                    <version>2.1.1</version>
                                                    <component>Concurrency</component>
                                        <votes>2</votes>
                                    <watches>11</watches>
                                                                                                                <comments>
                            <comment id="156580" author="antoine" created="Fri, 24 Aug 2012 21:26:33 +0000"  >&lt;p&gt;Just for the record from an email thread..&lt;br/&gt;
I was thinking this could be due to the &quot;journal commits under write lock&quot; that happen while the disks are busy with the fsync.&lt;br/&gt;
If writing the journal buffer to disk takes a while then db will block.&lt;/p&gt;
</comment>
                            <comment id="130478" author="jsr" created="Mon, 11 Jun 2012 19:04:43 +0000"  >&lt;p&gt;Attaching test results showing impact of sync delay. I only ran each test for 2 minutes. Would probably be good to run each one for longer periods of time. First worksheet of attached xls shows summary of each syncdelay setting for same workload. Subsequent pages have the raw data. &lt;/p&gt;</comment>
                            <comment id="119173" author="eliot" created="Mon, 14 May 2012 15:50:51 +0000"  >&lt;p&gt;Maybe.&lt;br/&gt;
Smoothing it out makes it worse in some cases.&lt;br/&gt;
Jared - you can play with --syncdelay&lt;br/&gt;
--syncdelay 1 will probably have no pause, but worse overall performance for example.&lt;/p&gt;</comment>
                            <comment id="119166" author="schwerin" created="Mon, 14 May 2012 15:47:51 +0000"  >&lt;p&gt;Presumably we&apos;re the party making the disk busy.  We might want, in the future, to at least smooth out this behavior, so that there aren&apos;t multi-second blocks in which no writes are possible.&lt;/p&gt;</comment>
                            <comment id="119159" author="eliot" created="Mon, 14 May 2012 15:43:48 +0000"  >&lt;p&gt;Not sure there is much we can do.&lt;br/&gt;
If the disk is busy its just busy.&lt;/p&gt;</comment>
                            <comment id="118907" author="jsr" created="Sun, 13 May 2012 15:58:53 +0000"  >&lt;p&gt;Journal on separate device seems to fix it. Here&apos;s output on an ec2 machine with journal &amp;amp; data volumes on their own EBS volumes: &lt;/p&gt;

&lt;p&gt; 42700      0      0      0       0       1       0  1.95g  4.66g   1.6g      0     50.1          0       0|0     0|1    23m     1k     2   15:51:19 &lt;br/&gt;
 33400      0      0      0       0       1       0  1.95g  4.66g  1.62g      0     62.1          0       0|0     0|1    18m     1k     2   15:51:20 &lt;br/&gt;
 34000      0      0      0       0       1       1  1.95g  4.66g  1.64g      0     77.3          0       0|0     0|1    18m     1k     2   15:51:21 &lt;br/&gt;
 37900      0      0      0       0       1       0  1.95g  4.66g  1.66g      0     65.9          0       0|0     0|1    20m     1k     2   15:51:22 &lt;br/&gt;
 47000      0      0      0       0       1       0  1.95g  4.66g  1.68g      1     59.5          0       0|0     0|1    25m     1k     2   15:51:23 &lt;/p&gt;</comment>
                            <comment id="118887" author="eliot" created="Sun, 13 May 2012 13:44:48 +0000"  >&lt;p&gt;Ah.&lt;br/&gt;
Could either be a block, or just the disk being super busy.&lt;br/&gt;
Can you try with journalling on but on a different device?&lt;br/&gt;
That should be the final test.&lt;/p&gt;</comment>
                            <comment id="118869" author="jsr" created="Sun, 13 May 2012 04:50:04 +0000"  >&lt;p&gt;BTW, running with --nojournal makes this go away. Could the journal group commit be blocked on completion of the background flush? &lt;/p&gt;


&lt;p&gt;output with mongod --nojournal &lt;/p&gt;

&lt;p&gt; 17500      0      0      0       0       1       0  5.95g  8.33g  1005m      103          0       0|0     0|1     9m     1k     2   21:46:55 &lt;br/&gt;
 11700      0      0      0       0       1       0  5.95g  8.33g  1012m     99.1          0       0|0     0|1     6m     1k     2   21:46:56 &lt;br/&gt;
 11800      0      0      0       0       1       0  5.95g  8.33g  1018m     99.5          0       0|0     0|1     6m     1k     2   21:46:57 &lt;br/&gt;
 21600      0      0      0       0       1       0  5.95g  8.33g  1.01g     98.8          0       0|0     0|1    11m     1k     2   21:46:58 &lt;br/&gt;
 15000      0      0      0       0       1       0  5.95g  8.33g  1.01g     99.3          0       0|0     0|1     8m     1k     2   21:46:59 &lt;br/&gt;
 12500      0      0      0       0       1       1  5.95g  8.33g  1.02g     98.7          0       0|0     0|1     6m     1k     2   21:47:00 &lt;br/&gt;
 58100      0      0      0       0       1       0  5.95g  8.33g  1.05g     86.2          0       0|0     0|1    31m     1k     2   21:47:01 &lt;/p&gt;
</comment>
                            <comment id="118868" author="jsr" created="Sun, 13 May 2012 04:26:10 +0000"  >&lt;p&gt;Are the db.serverStatus().backgroundFlushing stats useful? &lt;/p&gt;

&lt;p&gt;Here was the mongostat output during the pause: &lt;/p&gt;


&lt;p&gt; 14000      0      0      0       0       1       0  3.95g  10.3g  2.29g     96.7          0       0|0     0|1     7m     1k     3   21:17:03 &lt;br/&gt;
 11300      0      0      0       0       1       0  3.95g  10.3g  2.29g     95.6          0       0|0     0|1     6m     1k     3   21:17:04 &lt;br/&gt;
     0      0      0      0       0       1       0  3.95g  10.3g  2.29g        0          0       0|1     0|1    62b     1k     3   21:17:05 &lt;br/&gt;
  8400      0      0      0       0       1       1  3.95g  10.3g   2.3g      204          0       0|0     0|1     4m     1k     3   21:17:06 &lt;br/&gt;
 14000      0      0      0       0       1       0  3.95g  10.3g  2.31g     98.6          0       0|0     0|1     7m     1k     3   21:17:07 &lt;/p&gt;


&lt;p&gt;Here was the db.serverStatus().backgroundFlushing immediately after the pause &lt;/p&gt;


&lt;p&gt;&amp;gt; db.serverStatus().backgroundFlushing&lt;br/&gt;
{&lt;br/&gt;
	&quot;flushes&quot; : 144,&lt;br/&gt;
	&quot;total_ms&quot; : 32823,&lt;br/&gt;
	&quot;average_ms&quot; : 227.9375,&lt;br/&gt;
	&quot;last_ms&quot; : 1817,&lt;br/&gt;
	&quot;last_finished&quot; : ISODate(&quot;2012-05-13T04:17:05.776Z&quot;)&lt;br/&gt;
}&lt;/p&gt;
</comment>
                            <comment id="118867" author="schwerin" created="Sun, 13 May 2012 03:42:40 +0000"  >&lt;p&gt;Interesting.  2 questions.  1, is it possible to tell how long the flushAll() operation takes?  2, does it even make sense to periodically flush like this when durability is enabled?  The durability subsystem separately handles flushing the shared view to disk and committing journal writes, leaving open the question of why the background flush thread would even be necessary with durability.&lt;/p&gt;</comment>
                            <comment id="118865" author="jsr" created="Sun, 13 May 2012 03:08:50 +0000"  >&lt;p&gt;two writer processes: &lt;/p&gt;


&lt;p&gt; 19300      0      0      0       0       1       0  1.95g  6.32g  1.26g      105          0       0|1     0|2    10m     1k     3   20:05:01 &lt;br/&gt;
 18800      0      0      0       0       1       0  1.95g  6.32g  1.27g     93.3          0       0|1     0|2    10m     1k     3   20:05:02 &lt;br/&gt;
 19400      0      0      0       0       1       0  1.95g  6.32g  1.28g     94.8          0       0|1     0|2    10m     1k     3   20:05:03 &lt;br/&gt;
     0      0      0      0       0       1       0  1.95g  6.32g  1.28g        0          0       0|2     0|2    62b     1k     3   20:05:04 &lt;br/&gt;
insert  query update delete getmore command flushes mapped  vsize    res locked % idx miss %     qr|qw   ar|aw  netIn netOut  conn       time &lt;br/&gt;
     0      0      0      0       0       1       0  1.95g  6.32g  1.28g        0          0       1|2     0|2    62b     1k     3   20:05:05 &lt;br/&gt;
  8300      0      0      0       0       1       0  1.95g  6.32g  1.28g      310          0       0|1     0|2     4m     1k     3   20:05:06 &lt;br/&gt;
 16000      0      0      0       0       1       1  1.95g  6.32g  1.29g     95.2          0       0|1     0|2     8m     1k     3   20:05:08 &lt;br/&gt;
 17400      0      0      0       0       1       0  1.95g  6.32g   1.3g     92.5          0       0|1     0|2     9m     1k     3   20:05:09 &lt;/p&gt;

&lt;p&gt;three writer processes: &lt;/p&gt;

&lt;p&gt; 10100      0      0      0       0       1       0  3.95g  10.3g  1.89g     93.3          0       0|2     0|3     5m     1k     4   20:08:02 &lt;br/&gt;
 12400      0      0      0       0       1       0  3.95g  10.3g   1.9g      123          0       0|2     0|3     6m     1k     4   20:08:03 &lt;br/&gt;
  6000      0      0      0       0       1       0  3.95g  10.3g   1.9g     68.8          0       0|2     0|3     3m     1k     4   20:08:04 &lt;br/&gt;
     0      0      0      0       0       1       0  3.95g  10.3g   1.9g        0          0       1|3     0|3    62b     1k     4   20:08:05 &lt;br/&gt;
     0      0      0      0       0       1       0  3.95g  10.3g   1.9g        0          0       1|3     0|3    62b     1k     4   20:08:06 &lt;br/&gt;
  3200      0      0      0       0       1       1  3.95g  10.3g   1.9g      307          0       0|2     0|3     1m     1k     4   20:08:07 &lt;br/&gt;
  9600      0      0      0       0       1       0  3.95g  10.3g  1.91g     92.8          0       0|2     0|3     5m     1k     4   20:08:08 &lt;/p&gt;
</comment>
                            <comment id="118857" author="scotthernandez" created="Sun, 13 May 2012 01:47:32 +0000"  >&lt;p&gt;Can you run more than one process and see if the behavior changes?&lt;/p&gt;</comment>
                            <comment id="118856" author="jsr" created="Sun, 13 May 2012 01:34:15 +0000"  >&lt;p&gt;ext4. &lt;/p&gt;</comment>
                            <comment id="118855" author="eliot" created="Sun, 13 May 2012 01:25:57 +0000"  >&lt;p&gt;What linux filesystem?&lt;/p&gt;</comment>
                    </comments>
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                <attachments>
                            <attachment id="17138" name="sync delay analysis.xlsx" size="138912" author="jsr" created="Mon, 11 Jun 2012 19:04:43 +0000"/>
                            <attachment id="16562" name="writer.py" size="979" author="jsr" created="Sat, 12 May 2012 00:26:03 +0000"/>
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