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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>
    </build-info>


<item>
            <title>[DOCS-12252]  isMaster.compression documentation is misleading</title>
                <link>https://jira.mongodb.org/browse/DOCS-12252</link>
                <project id="10380" key="DOCS">Documentation</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Description&quot;&gt;&lt;/a&gt;Description&lt;/h2&gt;
&lt;p&gt;&lt;a href=&quot;https://docs.mongodb.com/manual/reference/command/isMaster/#isMaster.compression&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://docs.mongodb.com/manual/reference/command/isMaster/#isMaster.compression&lt;/a&gt; says:&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;An array listing the compression algorithms used to compress the current connection&apos;s network communication between the mongod or mongos and other members of the deployment or the mongo shell.&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;My understanding is ismaster.compression includes the compressors that have been negotiated between the client sending the ismaster request and the server responding, &lt;b&gt;for the particular ismaster request&lt;/b&gt;. For example, if the server is configured to use snappy,zlib:&lt;/p&gt;

&lt;p&gt;1. If the driver doesn&apos;t request any compression in ismaster, ismaster.compression is not returned at all, despite server potentially actively using it to compress communication between mongod/mongoses.&lt;br/&gt;
2. If the driver requests zlib only compression in ismaster, ismaster.compression will be zlib only, despite server potentially using snappy to compress mongod/mongos communication.&lt;br/&gt;
3. The ismaster request containing ismaster.compression, if it is part of the handshake, is not compressed (contrary to the &quot;used to compress the current connection&apos;s network communication&quot; language). Rather the compressor(s) returned in ismaster.compression &lt;b&gt;could&lt;/b&gt; be used by the driver to compress subsequent requests and by the server to compress subsequent responses, but neither side is obligated to perform compression (but is obligated to correctly handle incoming compressed data).&lt;br/&gt;
4. If compression has been negotiated on a given connection, and the ismaster request does not contain `compression` key, the the response&apos;s `compression` seems to indicate compression used by the current connection:&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;
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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;  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;=&amp;gt; #&amp;lt;Mongo::Operation::Result:0x47008169198800 documents=[{&quot;ismaster&quot;=&amp;gt;true, &quot;maxBsonObjectSize&quot;=&amp;gt;16777216, &quot;maxMessageSizeBytes&quot;=&amp;gt;48000000, &quot;maxWriteBatchSize&quot;=&amp;gt;100000, &quot;localTime&quot;=&amp;gt;2018-12-10 17:41:29 UTC, &quot;logicalSessionTimeoutMinutes&quot;=&amp;gt;30, &quot;connectionId&quot;=&amp;gt;4, &quot;minWireVersion&quot;=&amp;gt;0, &quot;maxWireVersion&quot;=&amp;gt;8, &quot;readOnly&quot;=&amp;gt;false, &quot;compression&quot;=&amp;gt;[&quot;zlib&quot;], &quot;ok&quot;=&amp;gt;1.0}]&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;However, if I specify a `compression` key on the request, the response&apos;s `compression` is the result of negotiation again:&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;irb(main):016:0&amp;gt; Mongoid.default_client.database.command(ismaster: 1,compression:[])&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;&amp;nbsp;&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;=&amp;gt; #&amp;lt;Mongo::Operation::Result:0x47008169274080 documents=[{&quot;ismaster&quot;=&amp;gt;true, &quot;maxBsonObjectSize&quot;=&amp;gt;16777216, &quot;maxMessageSizeBytes&quot;=&amp;gt;48000000, &quot;maxWriteBatchSize&quot;=&amp;gt;100000, &quot;localTime&quot;=&amp;gt;2018-12-10 17:41:26 UTC, &quot;logicalSessionTimeoutMinutes&quot;=&amp;gt;30, &quot;connectionId&quot;=&amp;gt;4, &quot;minWireVersion&quot;=&amp;gt;0, &quot;maxWireVersion&quot;=&amp;gt;8, &quot;readOnly&quot;=&amp;gt;false, &quot;ok&quot;=&amp;gt;1.0}]&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 seems that sending a `compression` argument in ismaster request changes the negotiated compression on the active connection, but I was unsuccessful in trying to brick the client by requesting `snappy` which the Ruby driver does not implement.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;Scopeofchanges&quot;&gt;&lt;/a&gt;Scope of changes&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;ImpacttoOtherDocs&quot;&gt;&lt;/a&gt;Impact to Other Docs&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;MVP%28WorkandDate%29&quot;&gt;&lt;/a&gt;MVP (Work and Date)&lt;/h2&gt;

&lt;h2&gt;&lt;a name=&quot;Resources%28ScopeorDesignDocs%2CInvision%2Cetc.%29&quot;&gt;&lt;/a&gt;Resources (Scope or Design Docs, Invision, etc.)&lt;/h2&gt;
</description>
                <environment></environment>
        <key id="648931">DOCS-12252</key>
            <summary> isMaster.compression documentation is misleading</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</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="3">Duplicate</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="oleg.pudeyev@mongodb.com">Oleg Pudeyev</reporter>
                        <labels>
                    </labels>
                <created>Mon, 10 Dec 2018 17:42:19 +0000</created>
                <updated>Mon, 10 Dec 2018 23:29:18 +0000</updated>
                            <resolved>Mon, 10 Dec 2018 23:27:34 +0000</resolved>
                                                    <fixVersion>DOCS-12251</fixVersion>
                                        <due></due>
                            <votes>0</votes>
                                    <watches>2</watches>
                                                                                                                    <issuelinks>
                            <issuelinktype id="10012">
                    <name>Related</name>
                                            <outwardlinks description="related to">
                                        <issuelink>
            <issuekey id="389211">RUBY-1216</issuekey>
        </issuelink>
                            </outwardlinks>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="648920">DOCS-12251</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="462299">DOCS-11045</issuekey>
        </issuelink>
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