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<title>mod_deflate - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.2</p>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.2</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache Module mod_deflate</h1>
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<p><span>Available Languages: </span><a href="../en/mod/mod_deflate.html" title="English"> en </a> |
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<a href="../ja/mod/mod_deflate.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="../ko/mod/mod_deflate.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Compress content before it is delivered to the
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>deflate_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_deflate.c</td></tr></table>
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<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module provides
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the <code>DEFLATE</code> output filter that allows output from
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your server to be compressed before being sent to the client over
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<div id="quickview"><h3 class="directives">Directives</h3>
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<li><img alt="" src="../images/down.gif" /> <a href="#deflatebuffersize">DeflateBufferSize</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#deflatecompressionlevel">DeflateCompressionLevel</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#deflatefilternote">DeflateFilterNote</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#deflatememlevel">DeflateMemLevel</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#deflatewindowsize">DeflateWindowSize</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#recommended">Sample Configurations</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#enable">Enabling Compression</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#proxies">Dealing with proxy servers</a></li>
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</ul><h3>See also</h3>
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<li><a href="../filter.html">Filters</a></li>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<h2><a name="recommended" id="recommended">Sample Configurations</a></h2>
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<p>This is a simple sample configuration for the impatient.</p>
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<div class="example"><h3>Compress only a few types</h3><p><code>
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AddOutputFilterByType DEFLATE text/html text/plain text/xml
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<p>The following configuration, while resulting in more compressed content,
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is also much more complicated. Do not use this unless you fully understand
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all the configuration details.</p>
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<div class="example"><h3>Compress everything except images</h3><p><code>
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<Location /><br />
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SetOutputFilter DEFLATE<br />
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# Netscape 4.x has some problems...<br />
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BrowserMatch ^Mozilla/4 gzip-only-text/html<br />
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# Netscape 4.06-4.08 have some more problems<br />
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BrowserMatch ^Mozilla/4\.0[678] no-gzip<br />
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# MSIE masquerades as Netscape, but it is fine<br />
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BrowserMatch \bMSIE !no-gzip !gzip-only-text/html<br />
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# Don't compress images<br />
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SetEnvIfNoCase Request_URI \<br />
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\.(?:gif|jpe?g|png)$ no-gzip dont-vary<br />
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# Make sure proxies don't deliver the wrong content<br />
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Header append Vary User-Agent env=!dont-vary<br />
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<h2><a name="enable" id="enable">Enabling Compression</a></h2>
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<h3><a name="output" id="output">Output Compression</a></h3>
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<p>Compression is implemented by the <code>DEFLATE</code>
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<a href="../filter.html">filter</a>. The following directive
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will enable compression for documents in the container where it
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<div class="example"><p><code>
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SetOutputFilter DEFLATE
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<p>Some popular browsers cannot handle compression of all content
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so you may want to set the <code>gzip-only-text/html</code> note to
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<code>1</code> to only allow html files to be compressed (see
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below). If you set this to <em>anything but <code>1</code></em> it
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<p>If you want to restrict the compression to particular MIME types
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in general, you may use the <code class="directive"><a href="../mod/core.html#addoutputfilterbytype">AddOutputFilterByType</a></code> directive. Here is an example of
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enabling compression only for the html files of the Apache
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<div class="example"><p><code>
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<Directory "/your-server-root/manual"><br />
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<span class="indent">
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AddOutputFilterByType DEFLATE text/html<br />
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<p>For browsers that have problems even with compression of all file
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types, use the <code class="directive"><a href="../mod/mod_setenvif.html#browsermatch">BrowserMatch</a></code> directive to set the <code>no-gzip</code>
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note for that particular browser so that no compression will be
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performed. You may combine <code>no-gzip</code> with <code>gzip-only-text/html</code> to get the best results. In that case
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the former overrides the latter. Take a look at the following
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excerpt from the <a href="#recommended">configuration example</a>
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defined in the section above:</p>
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<div class="example"><p><code>
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BrowserMatch ^Mozilla/4 gzip-only-text/html<br />
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BrowserMatch ^Mozilla/4\.0[678] no-gzip<br />
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BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
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<p>At first we probe for a <code>User-Agent</code> string that
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indicates a Netscape Navigator version of 4.x. These versions
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cannot handle compression of types other than
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<code>text/html</code>. The versions 4.06, 4.07 and 4.08 also
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have problems with decompressing html files. Thus, we completely
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turn off the deflate filter for them.</p>
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<p>The third <code class="directive"><a href="../mod/mod_setenvif.html#browsermatch">BrowserMatch</a></code>
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directive fixes the guessed identity of the user agent, because
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the Microsoft Internet Explorer identifies itself also as "Mozilla/4"
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but is actually able to handle requested compression. Therefore we
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match against the additional string "MSIE" (<code>\b</code> means
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"word boundary") in the <code>User-Agent</code> Header and turn off
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the restrictions defined before.</p>
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<div class="note"><h3>Note</h3>
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The <code>DEFLATE</code> filter is always inserted after RESOURCE
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filters like PHP or SSI. It never touches internal subrequests.
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<div class="note"><h3>Note</h3>
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There is a environment variable <code>force-gzip</code>,
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set via <code class="directive"><a href="../mod/core.html#setenv">SetEnv</a></code>, which
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will ignore the accept-encoding setting of your browser and will
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send compressed output.
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<h3><a name="inflate" id="inflate">Output Decompression</a></h3>
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<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
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inflating/uncompressing a gzip compressed response body. In order to activate
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this feature you have to insert the <code>INFLATE</code> filter into
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the outputfilter chain using <code class="directive"><a href="../mod/core.html#setoutputfilter">SetOutputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addoutputfilter">AddOutputFilter</a></code>, for example:</p>
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<div class="example"><p><code>
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<Location /dav-area><br />
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<span class="indent">
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ProxyPass http://example.com/<br />
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SetOutputFilter INFLATE<br />
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<p>This Example will uncompress gzip'ed output from example.com, so other
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filters can do further processing with it.
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<h3><a name="input" id="input">Input Decompression</a></h3>
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<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module also provides a filter for
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decompressing a gzip compressed request body . In order to activate
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this feature you have to insert the <code>DEFLATE</code> filter into
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the input filter chain using <code class="directive"><a href="../mod/core.html#setinputfilter">SetInputFilter</a></code> or <code class="directive"><a href="../mod/mod_mime.html#addinputfilter">AddInputFilter</a></code>, for example:</p>
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<div class="example"><p><code>
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<Location /dav-area><br />
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<span class="indent">
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SetInputFilter DEFLATE<br />
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<p>Now if a request contains a <code>Content-Encoding:
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gzip</code> header, the body will be automatically decompressed.
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Few browsers have the ability to gzip request bodies. However,
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some special applications actually do support request
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compression, for instance some <a href="http://www.webdav.org">WebDAV</a> clients.</p>
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<div class="warning"><h3>Note on Content-Length</h3>
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<p>If you evaluate the request body yourself, <em>don't trust
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the <code>Content-Length</code> header!</em>
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The Content-Length header reflects the length of the
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incoming data from the client and <em>not</em> the byte count of
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the decompressed data stream.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="proxies" id="proxies">Dealing with proxy servers</a></h2>
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<p>The <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> module sends a <code>Vary:
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Accept-Encoding</code> HTTP response header to alert proxies that
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a cached response should be sent only to clients that send the
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appropriate <code>Accept-Encoding</code> request header. This
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prevents compressed content from being sent to a client that will
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not understand it.</p>
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<p>If you use some special exclusions dependent
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on, for example, the <code>User-Agent</code> header, you must
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manually configure an addition to the <code>Vary</code> header
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to alert proxies of the additional restrictions. For example,
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in a typical configuration where the addition of the <code>DEFLATE</code>
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filter depends on the <code>User-Agent</code>, you should add:</p>
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<div class="example"><p><code>
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Header append Vary User-Agent
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<p>If your decision about compression depends on other information
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than request headers (<em>e.g.</em> HTTP version), you have to set the
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<code>Vary</code> header to the value <code>*</code>. This prevents
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compliant proxies from caching entirely.</p>
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<div class="example"><h3>Example</h3><p><code>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="DeflateBufferSize" id="DeflateBufferSize">DeflateBufferSize</a> <a name="deflatebuffersize" id="deflatebuffersize">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Fragment size to be compressed at one time by zlib</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateBufferSize <var>value</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateBufferSize 8096</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
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<p>The <code class="directive">DeflateBufferSize</code> directive specifies
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the size in bytes of the fragments that zlib should compress at one
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="DeflateCompressionLevel" id="DeflateCompressionLevel">DeflateCompressionLevel</a> <a name="deflatecompressionlevel" id="deflatecompressionlevel">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much compression do we apply to the output</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateCompressionLevel <var>value</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>Zlib's default</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
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<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>This directive is available since Apache 2.0.45</td></tr>
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<p>The <code class="directive">DeflateCompressionLevel</code> directive specifies
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what level of compression should be used, the higher the value,
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the better the compression, but the more CPU time is required to
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<p>The value must between 1 (less compression) and 9 (more compression).</p>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="DeflateFilterNote" id="DeflateFilterNote">DeflateFilterNote</a> <a name="deflatefilternote" id="deflatefilternote">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Places the compression ratio in a note for logging</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateFilterNote [<var>type</var>] <var>notename</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
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<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td><var>type</var> is available since Apache 2.0.45</td></tr>
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<p>The <code class="directive">DeflateFilterNote</code> directive
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specifies that a note about compression ratios should be attached
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to the request. The name of the note is the value specified for
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the directive. You can use that note for statistical purposes by
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adding the value to your <a href="../logs.html#accesslog">access log</a>.</p>
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<div class="example"><h3>Example</h3><p><code>
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DeflateFilterNote ratio<br />
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LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate<br />
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CustomLog logs/deflate_log deflate
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<p>If you want to extract more accurate values from your logs, you
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can use the <var>type</var> argument to specify the type of data
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left as note for logging. <var>type</var> can be one of:</p>
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<dt><code>Input</code></dt>
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<dd>Store the byte count of the filter's input stream in the note.</dd>
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<dt><code>Output</code></dt>
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<dd>Store the byte count of the filter's output stream in the note.</dd>
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<dt><code>Ratio</code></dt>
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<dd>Store the compression ratio (<code>output/input * 100</code>)
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in the note. This is the default, if the <var>type</var> argument
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<p>Thus you may log it this way:</p>
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<div class="example"><h3>Accurate Logging</h3><p><code>
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DeflateFilterNote Input instream<br />
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DeflateFilterNote Output outstream<br />
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DeflateFilterNote Ratio ratio<br />
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LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate<br />
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CustomLog logs/deflate_log deflate
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<li><code class="module"><a href="../mod/mod_log_config.html">mod_log_config</a></code></li>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="DeflateMemLevel" id="DeflateMemLevel">DeflateMemLevel</a> <a name="deflatememlevel" id="deflatememlevel">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>How much memory should be used by zlib for compression</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateMemLevel <var>value</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateMemLevel 9</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
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<p>The <code class="directive">DeflateMemLevel</code> directive specifies
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how much memory should be used by zlib for compression
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(a value between 1 and 9).</p>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="DeflateWindowSize" id="DeflateWindowSize">DeflateWindowSize</a> <a name="deflatewindowsize" id="deflatewindowsize">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Zlib compression window size</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>DeflateWindowSize <var>value</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>DeflateWindowSize 15</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_deflate</td></tr>
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<p>The <code class="directive">DeflateWindowSize</code> directive specifies the
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zlib compression window size (a value between 1 and 15). Generally, the
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higher the window size, the higher can the compression ratio be expected.</p>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_deflate.html" title="English"> en </a> |
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<a href="../ja/mod/mod_deflate.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="../ko/mod/mod_deflate.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
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