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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-58952] Implement operation to check if documents in collection have changed</title>
                <link>https://jira.mongodb.org/browse/SERVER-58952</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Is there a way to let users determine &quot;has db.myCollection changed at all since &amp;lt;time&amp;gt;&quot; that is more lightweight than opening a change stream and listening for change events?&lt;/p&gt;

&lt;p&gt;It would be useful to be able to check if a collection has changed in any way since some time.&lt;/p&gt;

&lt;p&gt;&lt;b&gt;Motivation&lt;/b&gt;&lt;/p&gt;

&lt;p&gt;The atlas search &quot;synonyms&quot; feature defines synonym data in a user collection. Search automatically detects changes to that collection, and updates synonyms artifacts on change.&lt;/p&gt;

&lt;p&gt;Search uses change streams to detect changes to that collection today - but does not have a way to incrementally modify synonym artifacts given change event information. mongot must replicate &quot;from scratch&quot; on each change.&lt;/p&gt;

&lt;p&gt;Change streams are an effective way to detect a change for a collection - but, if possible, we would be able to ask &quot;has this collection changed?&quot; in a less resource-intensive way.&lt;/p&gt;</description>
                <environment></environment>
        <key id="1835894">SERVER-58952</key>
            <summary>Implement operation to check if documents in collection have changed</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="backlog-query-execution">Backlog - Query Execution</assignee>
                                    <reporter username="evan.nixon@mongodb.com">Evan Nixon</reporter>
                        <labels>
                    </labels>
                <created>Thu, 29 Jul 2021 18:27:54 +0000</created>
                <updated>Fri, 24 Feb 2023 19:43:57 +0000</updated>
                                                                            <component>Catalog</component>
                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="5229894" author="oren.ovadia" created="Fri, 24 Feb 2023 19:43:57 +0000"  >&lt;p&gt;&amp;gt; Isn&apos;t there an optimization when there&apos;s&#160;&lt;tt&gt;ts&lt;/tt&gt;&#160;comparison that avoids scanning the entire oplog?&lt;br/&gt;
&#160;&lt;br/&gt;
Note we need to know of any change that happened to the collection as time advances, so even if we run a command like:&lt;/p&gt;
&lt;div class=&apos;table-wrap&apos;&gt;
&lt;table class=&apos;confluenceTable&apos;&gt;&lt;tbody&gt;
&lt;tr&gt;
&lt;td class=&apos;confluenceTd&apos;&gt;db.oplog.rs.count({ns: &quot;db.myCollection&quot;, ts: {$gte: &amp;lt;time&amp;gt;}})&lt;/td&gt;
&lt;/tr&gt;
&lt;/tbody&gt;&lt;/table&gt;
&lt;/div&gt;


&lt;p&gt;We will issue multiple ones where &amp;lt;time&amp;gt; increases for each one. So it would be very similar to using a changestream from our perspective at least.&lt;/p&gt;</comment>
                            <comment id="5226640" author="asya" created="Thu, 23 Feb 2023 20:50:58 +0000"  >&lt;p&gt;&amp;gt; It would still need to scan the whole oplog&lt;/p&gt;

&lt;p&gt;Isn&apos;t there an optimization when there&apos;s &lt;tt&gt;ts&lt;/tt&gt; comparison that avoids scanning the entire oplog?&lt;/p&gt;</comment>
                            <comment id="4955922" author="kateryna.kamenieva" created="Fri, 4 Nov 2022 17:57:49 +0000"  >&lt;p&gt;Moving to backlog, no plans for now to implement such a feature&lt;/p&gt;</comment>
                            <comment id="3998384" author="evan.nixon" created="Thu, 12 Aug 2021 19:11:46 +0000"  >&lt;p&gt;One alternative approach could be to directly query the oplog for events in a namespace after a specific time.&lt;/p&gt;

&lt;p&gt;This would scan a similar number of oplog documents as the change stream approach, but avoids overhead from transforming oplog entries to change events.&lt;/p&gt;</comment>
                            <comment id="3998379" author="charlie.swanson" created="Thu, 12 Aug 2021 19:07:38 +0000"  >&lt;p&gt;Could you try whether you could answer this with a query on the oplog? Something like&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.oplog.rs.count({ns: &lt;/span&gt;&lt;span style=&quot;color: blue; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;&quot;db.myCollection&quot;&lt;/span&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;, ts: {$gte: &amp;lt;time&amp;gt;}})&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 would still need to scan the whole oplog which is not as good as we could do with some custom logic, but it&apos;s worth a try as a speedup in the meantime.&lt;/p&gt;</comment>
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