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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-36601] WiredTigerLAS.wt does not shrink after major members are available</title>
                <link>https://jira.mongodb.org/browse/SERVER-36601</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;This is a&#160; follow up of&#160;&#160;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-36512&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;https://jira.mongodb.org/browse/SERVER-36512&lt;/a&gt;&#160;but this topic focuses on the issue happens after retriggering the issue of unlimited grows of lookaside&#160;table: WiredTigerLAS.wt.&lt;/p&gt;

&lt;p&gt;Details see&#160;&lt;span class=&quot;nobr&quot;&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/attachment/193839/193839_Issue+of+WiredTiger.wt+grows+unlimitedly+is+triggerable.pdf&quot; title=&quot;Issue of WiredTiger.wt grows unlimitedly is triggerable.pdf attached to SERVER-36601&quot;&gt;Issue of WiredTiger.wt grows unlimitedly is triggerable.pdf&lt;sup&gt;&lt;img class=&quot;rendericon&quot; src=&quot;https://jira.mongodb.org/images/icons/link_attachment_7.gif&quot; height=&quot;7&quot; width=&quot;7&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt;&lt;/sup&gt;&lt;/a&gt;&lt;/span&gt;&lt;/p&gt;

&lt;p&gt;I want to ask:&#160;&lt;/p&gt;

&lt;p&gt;1&amp;gt; Is it a bug that the&#160;WiredTigerLAS.wt cannot shrink to normal when the major data bearing member are available?&#160;&lt;/p&gt;

&lt;p&gt;2&amp;gt; a question: If it is the designed behavior that the lookaside&#160;table: WiredTigerLAS.wt grows unlimitedly till it uses out all the diskspace if major data bearing members are not available.&#160;&lt;/p&gt;

&lt;p&gt;If true, I would like to know if there is configuration option or something else to avoid&#160; WiredTigerLAS.wt stop halfway before it uses out all the disk space? As a user, I dislike this kind of behavior, I expect mongod can be smart enough to stop before the disk space used by&#160;WiredTigerLAS.wt reaching to a configured percent of disk space.&#160; Is this available or possible?&#160;&lt;/p&gt;

&lt;p&gt;Thanks&lt;/p&gt;

&lt;p&gt;Bruce&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="587076">SERVER-36601</key>
            <summary>WiredTigerLAS.wt does not shrink after major members are available</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</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="13202">Works as Designed</resolution>
                                        <assignee username="nick.brewer">Nick Brewer</assignee>
                                    <reporter username="brucezu">Bruce Zu</reporter>
                        <labels>
                    </labels>
                <created>Sun, 12 Aug 2018 05:55:05 +0000</created>
                <updated>Fri, 27 Oct 2023 13:53:36 +0000</updated>
                            <resolved>Mon, 13 Aug 2018 15:00:01 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="1974467" author="brucezu" created="Mon, 13 Aug 2018 18:45:41 +0000"  >&lt;p&gt;I got it. Nice!&#160;&lt;/p&gt;

&lt;p&gt;Thank you so much! Nick&lt;/p&gt;

&lt;p&gt;In my case: 1 primary, 2 secondary, 1 arbiter. The read concern&#160;majority number should be &amp;gt; 4 * (2 data bearning member)/( 4 member in replset)&lt;/p&gt;

&lt;p&gt;Suggest giving a precise description on how to calculate the majority in mongod&#160;document.&lt;/p&gt;

&lt;p&gt;Bruce&lt;/p&gt;</comment>
                            <comment id="1974460" author="nick.brewer" created="Mon, 13 Aug 2018 18:40:24 +0000"  >&lt;blockquote&gt;&lt;p&gt;I think there is a bug around there, in my case the calculated result is wrong.&#160; because only 1/3 data bearing member is unreachable.&#160;mongod.log can show it.&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;While only data-bearing members can satisfy a read concern majority, the majority is calculated against the &lt;b&gt;total&lt;/b&gt; number of nodes in the replica set, regardless of whether or not they contain any data. Thus two data bearing nodes and one arbiter do not satisfy the majority in your four member replica set. See&#160;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-31741&quot; title=&quot;WriteConcern - &amp;#39;majority&amp;#39; should not count aribiters&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-31741&quot;&gt;&lt;del&gt;SERVER-31741&lt;/del&gt;&lt;/a&gt;, which covers much of the same questions you&apos;re asking here, as well as the reason that this behavior is expected.&lt;/p&gt;

&lt;p&gt;-Nick&lt;/p&gt;</comment>
                            <comment id="1974432" author="brucezu" created="Mon, 13 Aug 2018 18:23:32 +0000"  >&lt;p&gt;Hi Nick&lt;/p&gt;

&lt;p&gt;How do you know &quot; your replica set does not have a sufficient number of data bearing members to satisfy the read concern&#160;&quot;&lt;/p&gt;

&lt;p&gt;Please do not judge it only from your picture. That is just the place there is a bug.&#160;&lt;/p&gt;

&lt;p&gt;I have shown you with the mongd.log in&#160;&lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-36512&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;https://jira.mongodb.org/browse/SERVER-36512&lt;/a&gt;&#160;and repeat more times in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-36597&quot; class=&quot;external-link&quot; rel=&quot;nofollow&quot;&gt;https://jira.mongodb.org/browse/SERVER-36597&lt;/a&gt;&#160;&lt;/p&gt;

&lt;p&gt;&lt;b&gt;lookaside table grows unlimited is the result, not the root reason for the issue.&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;Please focus on why mongo calculate out the major data bearing members are down. I think there is a bug around there, in my case the calculated result is wrong.&#160; because only 1/3 data bearing member is unreachable.&#160;mongod.log can show it.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;very regret to find&#160;lookaside table grows unlimited is designed behavior&lt;/p&gt;

&lt;p&gt;Thanks!&lt;/p&gt;

&lt;p&gt;Bruce&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</comment>
                            <comment id="1974045" author="nick.brewer" created="Mon, 13 Aug 2018 14:59:51 +0000"  >&lt;p&gt;&lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=brucezu&quot; class=&quot;user-hover&quot; rel=&quot;brucezu&quot;&gt;brucezu&lt;/a&gt; This issue is occurring because your replica set does not have a sufficient number of data bearing members to satisfy the read concern - in the example from your previous ticket, lookaside table growth began accruing over a period of days once one of the secondaries went down, due to the amount of information that was required to be stored in cache:&lt;/p&gt;

&lt;p&gt;&lt;span class=&quot;image-wrap&quot; style=&quot;&quot;&gt;&lt;a id=&quot;193868_thumb&quot; href=&quot;https://jira.mongodb.org/secure/attachment/193868/193868_Screen+Shot+2018-08-13+at+10.20.48+AM.png&quot; title=&quot;Screen Shot 2018-08-13 at 10.20.48 AM.png&quot; file-preview-type=&quot;image&quot; file-preview-id=&quot;193868&quot; file-preview-title=&quot;Screen Shot 2018-08-13 at 10.20.48 AM.png&quot;&gt;&lt;img src=&quot;https://jira.mongodb.org/secure/thumbnail/193868/_thumb_193868.png&quot; style=&quot;border: 0px solid black&quot; role=&quot;presentation&quot;/&gt;&lt;/a&gt;&lt;/span&gt;&lt;/p&gt;

&lt;p&gt;The red line in this graph represents the time (over a period of days) that your secondary was offline - you can see here that it directly lines up with the time when the lookaside table accumulated entries.&lt;/p&gt;
&lt;blockquote&gt;&lt;p&gt;Is it a bug that the WiredTigerLAS.wt cannot shrink to normal when the major data bearing member are available?&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;The content in the lookaside file is removed the next time that data is accessed, or when a table is dropped. However the recommended method for reclaiming the space is simply to reboot the mongod.&lt;/p&gt;
&lt;blockquote&gt;&lt;p&gt;If it is the designed behavior that the lookaside table: WiredTigerLAS.wt grows unlimitedly till it uses out all the diskspace if major data bearing members are not available.&lt;/p&gt;&lt;/blockquote&gt;
&lt;p&gt;If the replica set is left without enough data-bearing nodes for a long enough time - in this case multiple days - this is in fact the expected behavior. Replica sets are not intended to be left without a data-bearing majority for such an extended period of time.&lt;/p&gt;

&lt;p&gt;The behavior of the lookaside table mirrors the behavior of mongod in general - it cannot continue to operate if it runs out of available disk space.&lt;/p&gt;

&lt;p&gt;-Nick&lt;/p&gt;</comment>
                    </comments>
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                            <attachment id="193839" name="Issue of WiredTiger.wt grows unlimitedly is triggerable.pdf" size="103409" author="brucezu" created="Sun, 12 Aug 2018 05:43:06 +0000"/>
                            <attachment id="193868" name="Screen Shot 2018-08-13 at 10.20.48 AM.png" size="83523" author="nick.brewer" created="Mon, 13 Aug 2018 14:21:49 +0000"/>
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