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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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            <title>[SERVER-35699] Avoid holding locks during query parsing</title>
                <link>https://jira.mongodb.org/browse/SERVER-35699</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;Due to changes made in &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-29839&quot; title=&quot;Protect against UUID-&amp;gt;NSS mapping changing after looking it up in all commands that use parseNsOrUUID&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-29839&quot;&gt;&lt;del&gt;SERVER-29839&lt;/del&gt;&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-32367&quot; title=&quot;AutoGetCollectionOrView and its related classes perform shard version checking on a view&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-32367&quot;&gt;&lt;del&gt;SERVER-32367&lt;/del&gt;&lt;/a&gt; during 3.7 development, we now acquire locks prior to query parsing in the find command path. This is a behavior change in 4.0 compared to previous stable versions, which did not hold locks while parsing the query.&lt;/p&gt;

&lt;p&gt;Typically, parsing is fairly fast, but we have observed performance problems such as &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-35693&quot; title=&quot;Parsing of $in takes quadratic time due to O(n^2) boost::flat_set constructor&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-35693&quot;&gt;&lt;del&gt;SERVER-35693&lt;/del&gt;&lt;/a&gt; and &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-30189&quot; title=&quot;Reduce calls to allocator for large $in expressions&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-30189&quot;&gt;&lt;del&gt;SERVER-30189&lt;/del&gt;&lt;/a&gt; in which parsing was time consuming. Therefore, there is some risk of this behavior change causing performance problems on MMAPv1, where a MODE_S lock is held instead of a MODE_IS intent shared lock. Even on WiredTiger, there is some risk of this causing a performance problem---if the parsing phase can run for seconds or minutes without yielding its intent locks, then it is possible for an operation that requires a strong lock to be blocked, which in turn will block subsequent queued readers and writers waiting for intent locks.&lt;/p&gt;</description>
                <environment></environment>
        <key id="562027">SERVER-35699</key>
            <summary>Avoid holding locks during query parsing</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-optimization">Backlog - Query Optimization</assignee>
                                    <reporter username="david.storch@mongodb.com">David Storch</reporter>
                        <labels>
                    </labels>
                <created>Wed, 20 Jun 2018 15:23:45 +0000</created>
                <updated>Tue, 6 Dec 2022 03:26:00 +0000</updated>
                                            <version>4.0.0-rc6</version>
                                                    <component>Querying</component>
                                        <votes>0</votes>
                                    <watches>18</watches>
                                                                                                                <comments>
                            <comment id="1928751" author="ian@10gen.com" created="Fri, 22 Jun 2018 14:55:30 +0000"  >&lt;p&gt;Assigning to &lt;a href=&quot;https://jira.mongodb.org/secure/ViewProfile.jspa?name=david.storch&quot; class=&quot;user-hover&quot; rel=&quot;david.storch&quot;&gt;david.storch&lt;/a&gt; to figure out which team is best suited to makes these fixes.&lt;/p&gt;</comment>
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            <issuekey id="561704">SERVER-35693</issuekey>
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            <issuekey id="397687">SERVER-29839</issuekey>
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