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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-18875] Oplog performance on WT degrades over time after accumulation of deleted items</title>
                <link>https://jira.mongodb.org/browse/SERVER-18875</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;div class=&quot;panel&quot; style=&quot;background-color: #EEEEEE;border-color: #ccc;border-width: 1px;&quot;&gt;&lt;div class=&quot;panelHeader&quot; style=&quot;border-bottom-width: 1px;border-bottom-color: #ccc;background-color: #6CB33F;&quot;&gt;&lt;b&gt;Issue Status as of Jul 14, 2015&lt;/b&gt;&lt;/div&gt;&lt;div class=&quot;panelContent&quot; style=&quot;background-color: #EEEEEE;&quot;&gt;
&lt;p&gt;&lt;b&gt;ISSUE SUMMARY AND IMPACT&lt;/b&gt;&lt;br/&gt;
Capped collection handling in WiredTiger is inefficient because of way that WiredTiger tracks and expires documents in the capped collection. &lt;/p&gt;

&lt;p&gt;WiredTiger uses a specific internal cursor to find the &quot;beginning of the capped collection&quot;. Combined with asynchronous deletion of expired capped collection records, this is inefficient for collections with high numbers of inserts because requests have to process large number of expired documents.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;USER IMPACT&lt;/b&gt;&lt;br/&gt;
Capped collection performance degrades over time. Note that the &lt;a href=&quot;http://docs.mongodb.org/manual/core/replica-set-oplog/&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;oplog&lt;/a&gt; is a capped collection, so users running replica sets with WiredTiger may be impacted by this issue even if no other capped collections are used.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;RESOLUTION DETAILS&lt;/b&gt;&lt;br/&gt;
WiredTiger now caches the current &quot;first&quot; unexpired document in a capped collection. This change improves performance for all capped collections, but is particular important for the performance of replication because the oplog depends on capped collection performance.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;AFFECTED VERSIONS&lt;/b&gt;&lt;br/&gt;
MongoDB 3.0.0 through 3.0.4.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;FIX VERSION&lt;/b&gt;&lt;br/&gt;
The fix is included in the 3.0.5 production release.&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h6&gt;&lt;a name=&quot;Originaldescription&quot;&gt;&lt;/a&gt;Original description&lt;/h6&gt;
&lt;p&gt;Over the course of 2-3 days, running a simple insert workload with hammer, the performance of inserts degrades from about 20K/s to about 4K/s.&lt;br/&gt;
This was a single node replica set, writing locally to the master, using --nojournal to avoid intertwining any other potential issues.&lt;/p&gt;

&lt;p&gt;Perf indicates this:&lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;99.99% __curfile_next          mongo::WiredTigerRecordStore::cappedDeleteAsNeeded_inlock(mongo::OperationContext*, mongo::RecordId const&amp;amp;)&lt;/li&gt;
&lt;/ul&gt;

</description>
                <environment></environment>
        <key id="209236">SERVER-18875</key>
            <summary>Oplog performance on WT degrades over time after accumulation of deleted items</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="2" iconUrl="https://jira.mongodb.org/images/icons/priorities/critical.svg">Critical - P2</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="martin.bligh">Martin Bligh</assignee>
                                    <reporter username="martin.bligh">Martin Bligh</reporter>
                        <labels>
                            <label>WTcc</label>
                            <label>mms-s</label>
                    </labels>
                <created>Mon, 8 Jun 2015 19:54:23 +0000</created>
                <updated>Tue, 22 Sep 2015 02:33:35 +0000</updated>
                            <resolved>Mon, 13 Jul 2015 02:29:09 +0000</resolved>
                                                    <fixVersion>3.0.5</fixVersion>
                    <fixVersion>3.1.6</fixVersion>
                                    <component>WiredTiger</component>
                                        <votes>0</votes>
                                    <watches>20</watches>
                                                                                                                <comments>
                            <comment id="1016702" author="xgen-internal-githook" created="Fri, 28 Aug 2015 06:51:02 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;keithbostic&apos;, u&apos;name&apos;: u&apos;Keith Bostic&apos;, u&apos;email&apos;: u&apos;keith@wiredtiger.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt;: clean up some comments associated with cefeb2f, reorder a&lt;br/&gt;
test to do less work during checkpoint reconciliation.&lt;br/&gt;
Branch: develop&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/1685742d02f4f39f47b5d4a855674fd6dd49f097&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/1685742d02f4f39f47b5d4a855674fd6dd49f097&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="952796" author="xgen-internal-githook" created="Mon, 29 Jun 2015 05:23:19 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;michaelcahill&apos;, u&apos;name&apos;: u&apos;Michael Cahill&apos;, u&apos;email&apos;: u&apos;michael.cahill@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt; Don&apos;t keep deleted pages during a checkpoint.  Sync transaction up with WiredTiger 2.6 to ease back-porting, including picking up &lt;a href=&quot;https://jira.mongodb.org/browse/WT-1912&quot; title=&quot;Move eviction outside transactions&quot; class=&quot;issue-link&quot; data-issue-key=&quot;WT-1912&quot;&gt;&lt;del&gt;WT-1912&lt;/del&gt;&lt;/a&gt;.&lt;br/&gt;
Branch: mongodb-3.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/3751941f5339b257d9fd9c19879f1a901facfbb6&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/3751941f5339b257d9fd9c19879f1a901facfbb6&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="950129" author="xgen-internal-githook" created="Thu, 25 Jun 2015 04:41:40 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;agorrod&apos;, u&apos;name&apos;: u&apos;Alex Gorrod&apos;, u&apos;email&apos;: u&apos;alexander.gorrod@mongodb.com&apos;}
&lt;p&gt;Message: Merge pull request #2028 from wiredtiger/deleted-leaf-leak&lt;/p&gt;

&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt; Clean up deleted pages&lt;br/&gt;
Branch: develop&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/8f7da9ac596ed295228a792383bd5c03da205843&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/8f7da9ac596ed295228a792383bd5c03da205843&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="950128" author="xgen-internal-githook" created="Thu, 25 Jun 2015 04:41:39 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;michaelcahill&apos;, u&apos;name&apos;: u&apos;Michael Cahill&apos;, u&apos;email&apos;: u&apos;michael.cahill@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt; Track the checkpoint&apos;s session ID (rather than the transaction ID): changing visibility broke an assertion when releasing the checkpoint&apos;s transaction snapshot.&lt;br/&gt;
Branch: develop&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/35eece43f483f1a715a26556fd1f15a9a0a90ab3&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/35eece43f483f1a715a26556fd1f15a9a0a90ab3&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="950127" author="xgen-internal-githook" created="Thu, 25 Jun 2015 04:41:38 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;michaelcahill&apos;, u&apos;name&apos;: u&apos;Michael Cahill&apos;, u&apos;email&apos;: u&apos;michael.cahill@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt; During a checkpoint, don&apos;t keep data alive if the checkpoint is the only reader.&lt;/p&gt;

&lt;p&gt;In particular, if we see pages marked deleted at the beginning of a capped collection, don&apos;t cache those pages if there are no possible readers other than the checkpoint itself.&lt;br/&gt;
Branch: develop&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/847262185e60610a91e77e76ace5016c1cb8e736&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/847262185e60610a91e77e76ace5016c1cb8e736&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="950126" author="xgen-internal-githook" created="Thu, 25 Jun 2015 04:41:37 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;michaelcahill&apos;, u&apos;name&apos;: u&apos;Michael Cahill&apos;, u&apos;email&apos;: u&apos;michael.cahill@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-18875&quot; title=&quot;Oplog performance on WT degrades over time after accumulation of deleted items&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-18875&quot;&gt;&lt;del&gt;SERVER-18875&lt;/del&gt;&lt;/a&gt; Don&apos;t keep deleted pages around during a checkpoint if the checkpoint is the only potential reader.  Also, keep internal pages with deleted-but-not-yet-freed children dirty, so deleted leaf pages can&apos;t accumulate.&lt;br/&gt;
Branch: develop&lt;br/&gt;
&lt;a href=&quot;https://github.com/wiredtiger/wiredtiger/commit/cefeb2f6449460aff2146c85341438173143e7fa&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/wiredtiger/wiredtiger/commit/cefeb2f6449460aff2146c85341438173143e7fa&lt;/a&gt;&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10011">
                    <name>Depends</name>
                                            <outwardlinks description="depends on">
                                                        </outwardlinks>
                                                                <inwardlinks description="is depended on by">
                                        <issuelink>
            <issuekey id="212396">WT-1973</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10010">
                    <name>Duplicate</name>
                                                                <inwardlinks description="is duplicated by">
                                        <issuelink>
            <issuekey id="211595">SERVER-19031</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="213067">SERVER-19136</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="213618">SERVER-19178</issuekey>
        </issuelink>
                            </outwardlinks>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="206745">SERVER-18674</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="206780">SERVER-18677</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                    </issuelinks>
                <attachments>
                            <attachment id="78645" name="master-oplog-truncates-timeseries.png" size="96627" author="michael.cahill@mongodb.com" created="Fri, 19 Jun 2015 07:19:48 +0000"/>
                            <attachment id="78646" name="patched-oplog-truncates-timeseries.png" size="100180" author="michael.cahill@mongodb.com" created="Fri, 19 Jun 2015 07:19:48 +0000"/>
                            <attachment id="77112" name="sad_oplog.png" size="46503" author="martin.bligh" created="Mon, 8 Jun 2015 19:54:23 +0000"/>
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