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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-77840] Replace MurmurHash3 with absl::Hash if possible in FTSIndexFormat::_appendIndexKey</title>
                <link>https://jira.mongodb.org/browse/SERVER-77840</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;MurmurHash3 is a pretty old hash function that&apos;s slow and produces low-quality hashes compared to modern alternatives like absl::Hash (CityHash). We want to replace any uses of MurmurHash3 which are for in-memory use only, as we expect this to yield quick perf wins. Hash values that are persisted to disk across restarts or sent across the network between servers are likely unsafe to change, and should be annotated with a clear explanation for why the usage requires a stable hash computation.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2359803">SERVER-77840</key>
            <summary>Replace MurmurHash3 with absl::Hash if possible in FTSIndexFormat::_appendIndexKey</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="2">Won&apos;t Fix</resolution>
                                        <assignee username="ivan.fefer@mongodb.com">Ivan Fefer</assignee>
                                    <reporter username="dan.larkin-york@mongodb.com">Dan Larkin-York</reporter>
                        <labels>
                            <label>quick-tech-debt</label>
                    </labels>
                <created>Tue, 6 Jun 2023 16:15:14 +0000</created>
                <updated>Mon, 30 Oct 2023 17:52:34 +0000</updated>
                            <resolved>Mon, 30 Oct 2023 14:35:43 +0000</resolved>
                                                                                        <votes>0</votes>
                                    <watches>6</watches>
                                                                                                                <comments>
                            <comment id="5832549" author="xgen-internal-githook" created="Mon, 30 Oct 2023 17:52:34 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Ivan Fefer&apos;, &apos;email&apos;: &apos;ivan.fefer@mongodb.com&apos;, &apos;username&apos;: &apos;Fefer-Ivan&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-77840&quot; title=&quot;Replace MurmurHash3 with absl::Hash if possible in FTSIndexFormat::_appendIndexKey&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-77840&quot;&gt;&lt;del&gt;SERVER-77840&lt;/del&gt;&lt;/a&gt; Remove unused murmur3.h includes&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/c9e7bd4c4af13c9d98a69de485a3a4c1466a7eb9&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/c9e7bd4c4af13c9d98a69de485a3a4c1466a7eb9&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="5831163" author="JIRAUSER1270969" created="Mon, 30 Oct 2023 14:34:47 +0000"  >&lt;p&gt;Murmur hash is only used in legacy version 2 of full text index: &lt;a href=&quot;https://github.com/mongodb/mongo/blob/master/src/mongo/db/fts/fts_index_format.cpp#L198&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/master/src/mongo/db/fts/fts_index_format.cpp#L198&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;I am closing this ticket as Won&apos;t Fix&lt;/p&gt;</comment>
                            <comment id="5790382" author="JIRAUSER1270969" created="Thu, 19 Oct 2023 12:08:13 +0000"  >&lt;p&gt;Okay, funny thing. I didn&apos;t read the ticket title completely and started to replace murmur in other places. I actually almost completely removed murmur in favor of absl::Hash, but in FTS it must stay for legacy reasons.&lt;/p&gt;

&lt;p&gt;However, murmur is used in text index version 2 and the current version is text index version 3. This version uses md5 (since 2015).&lt;br/&gt;
The main goal of v3 was to support non-ICU unicode: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-19557&quot; title=&quot;Create Text Index v3&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-19557&quot;&gt;&lt;del&gt;SERVER-19557&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;We can in theory create text index version 4 that uses CityHash and test it&apos;s performance.&lt;/p&gt;</comment>
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