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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-12146] writeback listener may not get correct code back from ClientInfo::getLastError</title>
                <link>https://jira.mongodb.org/browse/SERVER-12146</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 January 2nd, 2014&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&lt;/b&gt;&lt;br/&gt;
Under very rare circumstances mongos may incorrectly report a write as successful.  The bug can manifest in the unlikely event that the mongos reuses a previously-used connection from the shared pool which contains a stale writeback field. In this situation, mongos cannot guarantee the correct post-migration location of writes and thus may incorrectly report the write as successful. Since mongos outgoing connections are tied to incoming client connections, this can only occur in cases of high connection turnover and low latency. The bug is difficult to trigger, but has caused a lost write in one known case.&lt;/p&gt;

&lt;p&gt;This race condition can only occur on the first occurrence of a writeback being queued for a shard. Once a writeback is queued, the connection is cached.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;USER IMPACT&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;&lt;b&gt;Affected Version:&lt;/b&gt; All versions of MongoDB prior to and including v2.4.8.&lt;br/&gt;
&lt;b&gt;Conditions Required:&lt;/b&gt; Sharded cluster with balancing enabled and active.&lt;br/&gt;
&lt;b&gt;Frequency:&lt;/b&gt; Extremely rare.&lt;br/&gt;
&lt;b&gt;Root Cause:&lt;/b&gt; In certain cases, it is possible for the getLastError aggregation in mongos ClientInfo to not return the correct code to the writeback listener.  We ignore any previous writebacks when reprocessing a write in the writeback listener, but incorrectly do not append the other getLastError fields contained in &quot;res&quot; (the getLastError result from the shard).&lt;/p&gt;

&lt;p&gt;In short, when retrying a write via the writeback listener, it is possible for the writeback listener to miss the special stale config code it needs to continue retrying.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;SOLUTION&lt;/b&gt;&lt;br/&gt;
Always aggregate results from getLastError even in the presence of previous writebacks.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;WORKAROUNDS&lt;/b&gt;&lt;br/&gt;
Temporarily disable the balancer until all mongos are updated to ensure your sharded cluster is not susceptible to this bug.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;PATCHES&lt;/b&gt;&lt;br/&gt;
Production release v2.4.9 and v2.2.7 contain the fix for this issue, and production release v2.6.0 will contain the fix as well.  Upgrading all mongos processes to MongoDB v2.4.9 or MongoDB v2.2.7 is required to avoid this issue.&lt;/p&gt;
&lt;/div&gt;&lt;/div&gt;

&lt;h4&gt;&lt;a name=&quot;OriginalDescription&quot;&gt;&lt;/a&gt;Original Description&lt;/h4&gt;

&lt;p&gt;In certain cases, it seems possible for the getLastError aggregation in mongos ClientInfo to not return the correct code to the writeback listener.&lt;/p&gt;

&lt;p&gt;The core issue is here:&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;
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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;
					&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;            if ( writebacks.size() ){&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;                vector&amp;lt;BSONObj&amp;gt; v = _handleWriteBacks( writebacks , fromWriteBackListener );&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;                if ( v.size() == 0 &amp;amp;&amp;amp; fromWriteBackListener ) {&lt;/span&gt;&lt;/pre&gt;
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						&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;                    // ok&lt;/span&gt;&lt;/pre&gt;
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						&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;
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						&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;
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						&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;            else {&lt;/span&gt;&lt;/pre&gt;
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						&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;                result.append( &quot;singleShard&quot; , theShard );&lt;/span&gt;&lt;/pre&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  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;/table&gt;
&lt;/div&gt;
&lt;p/&gt;

&lt;p&gt;We ignore any writebacks when reprocessing a write in the WBL, but incorrectly do not append the other getLastError fields contained in &quot;res&quot; (the getLastError result from the shard).&lt;/p&gt;

&lt;p&gt;In short, when retrying a command in the WBL, it&apos;s possible for the WBL to not get the special stale config code it needs to continue retrying.&lt;/p&gt;</description>
                <environment></environment>
        <key id="102960">SERVER-12146</key>
            <summary>writeback listener may not get correct code back from ClientInfo::getLastError</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="greg_10gen">Greg Studer</assignee>
                                    <reporter username="greg_10gen">Greg Studer</reporter>
                        <labels>
                    </labels>
                <created>Tue, 17 Dec 2013 21:02:16 +0000</created>
                <updated>Mon, 11 Jul 2016 17:40:19 +0000</updated>
                            <resolved>Sat, 21 Dec 2013 15:48:02 +0000</resolved>
                                                    <fixVersion>2.2.7</fixVersion>
                    <fixVersion>2.4.9</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>13</watches>
                                                                                                                <comments>
                            <comment id="477642" author="xgen-internal-githook" created="Mon, 6 Jan 2014 15:57:23 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;monkey101&apos;, u&apos;name&apos;: u&apos;Dan Pasette&apos;, u&apos;email&apos;: u&apos;dan@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-12146&quot; title=&quot;writeback listener may not get correct code back from ClientInfo::getLastError&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-12146&quot;&gt;&lt;del&gt;SERVER-12146&lt;/del&gt;&lt;/a&gt; do not check writebacks if calling gle from wbl&lt;br/&gt;
Branch: v2.2&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/307fb42c66350981525d64ca8f6a2dbfe6a3d8f4&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/307fb42c66350981525d64ca8f6a2dbfe6a3d8f4&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="476503" author="dan@10gen.com" created="Thu, 2 Jan 2014 18:02:25 +0000"  >&lt;p&gt;This patch will be backported to the 2.2 branch.&lt;/p&gt;</comment>
                            <comment id="474069" author="xgen-internal-githook" created="Sat, 21 Dec 2013 14:49:55 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;username&apos;: u&apos;monkey101&apos;, u&apos;name&apos;: u&apos;Dan Pasette&apos;, u&apos;email&apos;: u&apos;dan@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-12146&quot; title=&quot;writeback listener may not get correct code back from ClientInfo::getLastError&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-12146&quot;&gt;&lt;del&gt;SERVER-12146&lt;/del&gt;&lt;/a&gt; do not check writebacks if calling gle from wbl&lt;br/&gt;
Branch: v2.4&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/bd3553dff93786447130c242c274678f969cd513&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/bd3553dff93786447130c242c274678f969cd513&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="473220" author="greg_10gen" created="Thu, 19 Dec 2013 18:03:05 +0000"  >&lt;p&gt;Attached test case reproduces with two fail points in the WBL - difficult to trigger deterministically.&lt;/p&gt;</comment>
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                            <attachment id="35593" name="writeback_retry.js" size="3731" author="greg_10gen" created="Thu, 19 Dec 2013 18:03:04 +0000"/>
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