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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-5928] Non-atomic upsert</title>
                <link>https://jira.mongodb.org/browse/SERVER-5928</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I was under impression, that update w/upsert is atomic (since it operates on a single, though maybe not-yet-existing document). Unfortunately, when under moderate load we see duplicate key errors on &lt;em&gt;id for upsert operations. I&apos;ve read the docs and got the impression that $atomic modifier is not a solution (docs describe it as a way to do _multiple&lt;/em&gt; document updates concurrently). Is there something broken in the server, documentation or my own head? =) If it&apos;s a documentation issue (I suspect that, but I feel sorry for myself updating all our code that uses upserts), please update the docs with a clear statement that &quot;upsert still can fail on non-unique IDs, use XXX instead&quot;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="39592">SERVER-5928</key>
            <summary>Non-atomic upsert</summary>
                <type id="6" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14720&amp;avatarType=issuetype">Question</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="tyler@10gen.com">Tyler Brock</assignee>
                                    <reporter username="onyxmaster">Aristarkh Zagorodnikov</reporter>
                        <labels>
                    </labels>
                <created>Fri, 25 May 2012 07:55:28 +0000</created>
                <updated>Thu, 6 Mar 2014 23:58:37 +0000</updated>
                            <resolved>Wed, 30 May 2012 19:53:42 +0000</resolved>
                                    <version>2.0.5</version>
                                                    <component>Write Ops</component>
                                        <votes>0</votes>
                                    <watches>0</watches>
                                                                                                                <comments>
                            <comment id="128126" author="auto" created="Thu, 7 Jun 2012 19:00:24 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{u&apos;login&apos;: u&apos;tychoish&apos;, u&apos;name&apos;: u&apos;Sam Kleinman&apos;, u&apos;email&apos;: u&apos;samk@10gen.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-5928&quot; title=&quot;Non-atomic upsert&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-5928&quot;&gt;&lt;del&gt;SERVER-5928&lt;/del&gt;&lt;/a&gt; clarifying upsert documentation&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/docs/commit/28d3c27efff41ef443ff380d6e1f9eede374ea8c&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/docs/commit/28d3c27efff41ef443ff380d6e1f9eede374ea8c&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="124502" author="onyxmaster" created="Wed, 30 May 2012 19:57:48 +0000"  >&lt;p&gt;Good to hear, thanks for the update.&lt;/p&gt;</comment>
                            <comment id="124496" author="tyler@10gen.com" created="Wed, 30 May 2012 19:52:18 +0000"  >&lt;p&gt;Ok, I totally agree the documentation should be as good as possible. Thank you for bringing it up.&lt;/p&gt;

&lt;p&gt;I&apos;ve improved some of the update() docs to make it a little more clear that the determining factor for whether or not to do an update or insert comes from the criteria document passed as the first argument to update.&lt;/p&gt;</comment>
                            <comment id="124305" author="onyxmaster" created="Wed, 30 May 2012 14:20:51 +0000"  >&lt;p&gt;Yes, your explanation is perfect, having something like that in docs near &quot;upsert&quot; surely would prevent surprising problems. And I understand that MongoDB doesn&apos;t do anyting &quot;smart&quot;, I was just pointing out that it doesn&apos;t and in my opinion shouldn&apos;t =)&lt;/p&gt;</comment>
                            <comment id="124293" author="tyler@10gen.com" created="Wed, 30 May 2012 13:51:45 +0000"  >&lt;p&gt;Hey Aristarkh,&lt;/p&gt;

&lt;p&gt;Thank you for posting the code. Let&apos;s go through what is happening first so we are on the same page before we address the question.&lt;/p&gt;

&lt;p&gt;The problem here is that the &lt;tt&gt;doc.version&lt;/tt&gt; is still 2 on the second update.&lt;/p&gt;

&lt;p&gt;The variable &lt;tt&gt;doc&lt;/tt&gt; still contains the document retrieved by the initial findOne query. When you go to do a subsequent upsert the expression actually looks like this after being evaluated by javascript but before the query is run:&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;   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;db.test.update({_id:1, version:2},{$set:{data:3}, $inc:{version:1}}, true);&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;This is an upsert, and so, because that document doesn&apos;t exist, MongoDB tries to insert it and fails.&lt;/p&gt;

&lt;p&gt;It fails because document with the key _id equal to 1 is already in the collection and there is a unique index on that field. There can&apos;t be any other documents in the collection with that same key value.&lt;/p&gt;

&lt;p&gt;Now, to answer you question, MongoDB is not doing anything smart here. I believe you are interpreting this behavior as Mongo looking to see if _id, the non-unique key, is non unique before inserting. That is not the case.&lt;/p&gt;

&lt;p&gt;What happens is Mongo queries for a document that matches the query document portion of the update:&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;   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;{_id: 1, version: 2}&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;It does not exist. This normally means that no update should occur, but because you are performing an upsert, Mongo attempts to insert the document and fails, because the _id is not unique.&lt;/p&gt;

&lt;p&gt;Let me know if that makes sense. If this is at all unclear please let me know so we can update our documentation appropriately.&lt;/p&gt;</comment>
                            <comment id="123470" author="onyxmaster" created="Sun, 27 May 2012 19:22:22 +0000"  >&lt;p&gt;The following JS code should better illustrate what am I doing:&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 test document&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;&amp;gt; db.test.insert({_id:1, version:2, data:3})&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;// Get current document&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;&amp;gt; var doc = db.test.findOne({_id:1});&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;&amp;gt; printjson(doc);&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;{&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;        &quot;_id&quot; : 1,&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;        &quot;version&quot; : 2,&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;        &quot;data&quot; : 3&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;}&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;// Perform some updates on doc.data&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;...&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;// Update&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;&amp;gt; db.test.update({_id:1, version:doc.version},{$set:{data:doc.data}, $inc:{version:1}}, true);db.getLastError();&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;// Update succeeded&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;null&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;// Try once more&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;&amp;gt; db.test.update({_id:1, version:doc.version},{$set:{data:doc.data}, $inc:{version:1}}, true);&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;// Failed with &quot;non-unique key&quot; since &quot;version&quot; field changed&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;E11000 duplicate key error index: d2_feed0.feed.$_id_  dup key: { : 1 }&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 think that MongoDB should not try be &quot;smarter&quot; and filter out non-unique index keys before querying to prevent this (when I first encountered this, I expected having &quot;affected documents count&quot; being zero instead of &quot;non-unique key&quot; error), but the current mechanism hurts learnability (you do query on _id only and everything works as expected, you add another fields and you get unexpected error that is not easy to grasp at first). I propose only documentation improvements, not the core server changes (unless that&apos;s the plan).&lt;/p&gt;</comment>
                            <comment id="123452" author="eliot" created="Sun, 27 May 2012 13:12:29 +0000"  >&lt;p&gt;Can you try this with a 2.1 nightly?&lt;/p&gt;</comment>
                            <comment id="123434" author="onyxmaster" created="Sun, 27 May 2012 05:57:04 +0000"  >&lt;p&gt;I never asked about multiple updates (the documentation is pretty clear about this), please pay attention when reading ticket description.&lt;br/&gt;
I was talking about upsert functionality and how it operates unexpectedly, returning &quot;duplicate key error&quot;, when one uses upsert with (for example) two fields in &quot;query&quot; part of the update operation.&lt;br/&gt;
In our code this pattern is very common, since we use it to perform version-based optimistic concurrency updates: update the document only if it&apos;s &quot;version&quot; (actually the &quot;v&quot; field) didn&apos;t change between read and write, incrementing it, elseway repeat the read-modify-write cycle. This leads us to requirement that query should be compound (&lt;/p&gt;
{ _id: &amp;lt;some_id&amp;gt;, v: &amp;lt;current_version&amp;gt; }
&lt;p&gt;). If the document is updated in some other thread, update can&apos;t match the &quot;v&quot; part of the query and tries to insert document.&lt;/p&gt;</comment>
                            <comment id="123178" author="tyler@10gen.com" created="Fri, 25 May 2012 16:38:12 +0000"  >&lt;p&gt;Atomicity within MongoDB is at the document level.&lt;/p&gt;

&lt;p&gt;There is currently no way to do multiple updates concurrently unless those updates use the atomic modifiers ($inc, $set, etc...) to modify a single document.&lt;/p&gt;

&lt;p&gt;To update multiple documents atomically you would need transaction support which does not currently exist in mongodb.&lt;/p&gt;</comment>
                            <comment id="123176" author="tyler@10gen.com" created="Fri, 25 May 2012 16:35:41 +0000"  >&lt;p&gt;Aristark could you post a the query you are having trouble with?&lt;/p&gt;</comment>
                            <comment id="123014" author="onyxmaster" created="Fri, 25 May 2012 08:41:12 +0000"  >&lt;p&gt;Yes, this is definitely the case. Sorry for bothering you with this. The &quot;Upsert with modifiers&quot; section of &lt;a href=&quot;http://www.mongodb.org/display/DOCS/Updating&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://www.mongodb.org/display/DOCS/Updating&lt;/a&gt; (or the new manual) should have something on this topic.&lt;/p&gt;</comment>
                            <comment id="123010" author="onyxmaster" created="Fri, 25 May 2012 08:15:48 +0000"  >&lt;p&gt;It appears that the root cause in my case is that query is compound one.&lt;/p&gt;</comment>
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