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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>[SERVER-3663] Mongod on windows performance degrades over time</title>
                <link>https://jira.mongodb.org/browse/SERVER-3663</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Started mongod in windows and ran manyConnectionsTest.py from my mac in 3 different shells.&lt;br/&gt;
Read and write performance would initially fluctuate but eventually level off a couple minutes after all client threads were up and running.  There would then periodically be periods of time where the read and write rate fluctuated wildly, before eventually re-stabilizing with worse performance.  After a few of those, the periods of performance fluctuation would go away, and instead the performance would degrade gradually.&lt;/p&gt;

&lt;p&gt;For one such run, performance initially stabilized at roughly 2000 reads/sec and 180 writes/sec.  After a period of fluctuating read and write rates, it re-stabilized at 2000 reads/sec with only 128 writes/sec.  After another burst of unstable performance, it re-stabilized at roughly 700 reads/sec and 83 writes/sec.  Then there was no more great variability in performance - instead the write rate went slowly but steadily down as the read rate slowly went up.  I checked in periodically and saw QPSs of 718 reads/sec w/ 61 writes/sec, 733 reads/sec w/ 46 writes/sec, 755 reads/sec w/ 23 writes/sec, and 763 reads/sec w/ 163 writes/sec.  At around this point, performance suddenly fell away to zero.&lt;/p&gt;

&lt;p&gt;At this point, the python processes running manyConnectionsTest froze, printing an error message saying the find_one operation timed out.&lt;/p&gt;


&lt;p&gt;At this point, however, it was still possible to create new connections to the mongod, and it could process queries from those new connections.&lt;/p&gt;</description>
                <environment>Windows 64 bit&lt;br/&gt;
MongoDB 64 bit 1.8.2 and 2.0&lt;br/&gt;
Python 2.6.1&lt;br/&gt;
pymongo 2.0.1</environment>
        <key id="21303">SERVER-3663</key>
            <summary>Mongod on windows performance degrades over time</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="9">Done</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="spencer@mongodb.com">Spencer Brody</reporter>
                        <labels>
                            <label>Windows</label>
                    </labels>
                <created>Mon, 22 Aug 2011 15:57:07 +0000</created>
                <updated>Thu, 17 Mar 2016 15:04:07 +0000</updated>
                            <resolved>Thu, 17 Mar 2016 15:04:07 +0000</resolved>
                                    <version>1.8.2</version>
                    <version>2.0.0-rc0</version>
                                                    <component>Performance</component>
                    <component>Stability</component>
                                        <votes>2</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="78350" author="dwight_10gen" created="Sat, 7 Jan 2012 18:32:10 +0000"  >&lt;p&gt;for non-SRM, if we wrapped everything with a semaphore allowing say, 100 masximum concurrent actors, probably probably goes away.&lt;br/&gt;
this might be a good idea anyway : once all cores and disks are saturdated more interleaving is not helpful but rather hurtful for performance&lt;/p&gt;</comment>
                            <comment id="52419" author="dwight_10gen" created="Sun, 4 Sep 2011 17:25:40 +0000"  >&lt;p&gt;this seems to be because of thread contention with ~1000 threads and slow writes.  it then behaves poorly.&lt;/p&gt;

&lt;p&gt;using SlimReaderWriterLock solves on windows.  so we need to have a built that way.&lt;/p&gt;

&lt;p&gt;also need to test on a couple of other platforms may happen elsewhere.  if the rwlock is done by the OS then it is probably ok as the scheduler will be aware &amp;#8211; so probably ok on Linux.&lt;/p&gt;</comment>
                            <comment id="50232" author="eliot" created="Tue, 23 Aug 2011 21:12:30 +0000"  >&lt;p&gt;@dwight - any ideas?  if not - can re-assign for a deeper dive&lt;/p&gt;</comment>
                            <comment id="49953" author="spencer" created="Mon, 22 Aug 2011 18:39:03 +0000"  >&lt;p&gt;Tried to reproduce on linux and failed.&lt;/p&gt;</comment>
                    </comments>
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                            <attachment id="12751" name="manyConnectionsTest.py" size="1840" author="spencer@mongodb.com" created="Mon, 22 Aug 2011 15:57:07 +0000"/>
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