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4647c3d043
as a MCacheMinObjectSize of 0 does not make sense and leads to a signal Floating point exception (8) (division by zero) in memcache_gdsf_algorithm. PR: 40576 Submitted by: Xuekun Hu <xuekun.hu gmail.com> Reviewed by: rpluem git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@469895 13f79535-47bb-0310-9956-ffa450edef68
218 lines
8.5 KiB
XML
218 lines
8.5 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<modulesynopsis metafile="mod_mem_cache.xml.meta">
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<name>mod_mem_cache</name>
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<description>Content cache keyed to URIs</description>
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<status>Extension</status>
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<sourcefile>mod_mem_cache.c</sourcefile>
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<identifier>mem_cache_module</identifier>
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<summary>
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<p>This module <em>requires</em> the service of <module
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>mod_cache</module>. It acts as a support module for <module
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>mod_cache</module> and provides a memory based storage manager.
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<module>mod_mem_cache</module> can be configured to operate in two
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modes: caching open file descriptors or caching objects in heap storage.
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<module>mod_mem_cache</module> is most useful when used to cache locally
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generated content or to cache backend server content for <module
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>mod_proxy</module> configured for <directive module="mod_proxy"
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>ProxyPass</directive> (aka <dfn>reverse proxy</dfn>).</p>
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<p>Content is stored in and retrieved from the cache using URI based
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keys. Content with access protection is not cached.</p>
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</summary>
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<seealso><module>mod_cache</module></seealso>
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<seealso><module>mod_disk_cache</module></seealso>
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<directivesynopsis>
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<name>MCacheSize</name>
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<description>The maximum amount of memory used by the cache in
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KBytes</description>
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<syntax>MCacheSize <var>KBytes</var></syntax>
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<default>MCacheSize 100</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The <directive>MCacheSize</directive> directive sets the maximum
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amount of memory to be used by the cache, in KBytes (1024-byte units).
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If a new object needs to be inserted in the cache and the size of the
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object is greater than the remaining memory, objects will be removed
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until the new object can be cached. The object to be removed is
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selected using the algorithm specified by <directive
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module="mod_mem_cache">MCacheRemovalAlgorithm</directive>.</p>
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<example><title>Example</title>
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MCacheSize 700000
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</example>
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<note><title>Note</title>
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<p>The <directive>MCacheSize</directive> value must be greater than
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the value specified by the <directive module="mod_mem_cache"
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>MCacheMaxObjectSize</directive> directive.</p>
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</note>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>MCacheMaxObjectCount</name>
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<description>The maximum number of objects allowed to be placed in the
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cache</description>
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<syntax>MCacheMaxObjectCount <var>value</var></syntax>
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<default>MCacheMaxObjectCount 1009</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The <directive>MCacheMaxObjectCount</directive> directive sets the
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maximum number of objects to be cached. The value is used to create the
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open hash table. If a new object needs to be inserted in the cache and
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the maximum number of objects has been reached, an object will be
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removed to allow the new object to be cached. The object to be removed
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is selected using the algorithm specified by <directive
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module="mod_mem_cache">MCacheRemovalAlgorithm</directive>.</p>
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<example><title>Example</title>
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MCacheMaxObjectCount 13001
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>MCacheMinObjectSize</name>
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<description>The minimum size (in bytes) of a document to be allowed in the
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cache</description>
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<syntax>MCacheMinObjectSize <var>bytes</var></syntax>
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<default>MCacheMinObjectSize 1</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The <directive>MCacheMinObjectSize</directive> directive sets the
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minimum size in bytes of a document for it to be considered
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cacheable.</p>
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<example><title>Example</title>
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MCacheMinObjectSize 10000
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>MCacheMaxObjectSize</name>
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<description>The maximum size (in bytes) of a document allowed in the
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cache</description>
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<syntax>MCacheMaxObjectSize <var>bytes</var></syntax>
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<default>MCacheMaxObjectSize 10000</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The <directive>MCacheMaxObjectSize</directive> directive sets the
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maximum allowable size, in bytes, of a document for it to be considered
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cacheable.</p>
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<example><title>Example</title>
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MCacheMaxObjectSize 6400000
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</example>
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<note><title>Note</title>
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<p>The value of <directive>MCacheMaxObjectSize</directive> must be
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greater than the value specified by the <directive
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module="mod_mem_cache">MCacheMinObjectSize</directive> directive.</p>
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</note>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>MCacheRemovalAlgorithm</name>
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<description>The algorithm used to select documents for removal from the
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cache</description>
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<syntax>MCacheRemovalAlgorithm LRU|GDSF</syntax>
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<default>MCacheRemovalAlgorithm GDSF</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The <directive>MCacheRemovalAlgorithm</directive> directive specifies
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the algorithm used to select documents for removal from the cache.
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Two choices are available:</p>
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<dl>
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<dt><code>LRU</code> (Least Recently Used)</dt>
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<dd><code>LRU</code> removes the documents that have not been accessed
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for the longest time.</dd>
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<dt><code>GDSF</code> (GreadyDual-Size)</dt>
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<dd><code>GDSF</code> assigns a priority to cached documents based
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on the cost of a cache miss and the size of the document. Documents
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with the lowest priority are removed first.</dd>
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</dl>
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<example><title>Example</title>
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MCacheRemovalAlgorithm GDSF<br />
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MCacheRemovalAlgorithm LRU
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>MCacheMaxStreamingBuffer</name>
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<description>Maximum amount of a streamed response to buffer in memory
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before declaring the response uncacheable</description>
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<syntax>MCacheMaxStreamingBuffer <var>size_in_bytes</var></syntax>
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<default>MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize</default>
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<contextlist><context>server config</context>
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</contextlist>
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<usage>
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<p>The <directive>MCacheMaxStreamingBuffer</directive> directive
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specifies the maximum number of bytes of a streamed response to
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buffer before deciding that the response is too big to cache.
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A streamed response is one in which the entire content is not
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immediately available and in which the <code>Content-Length</code>
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may not be known. Sources of streaming responses include proxied
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responses and the output of CGI scripts. By default, a streamed
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response will <em>not</em> be cached unless it has a
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<code>Content-Length</code> header. The reason for this is to
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avoid using a large amount of memory to buffer a partial response
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that might end up being too large to fit in the cache.
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The <directive>MCacheMaxStreamingBuffer</directive> directive allows
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buffering of streamed responses that don't contain a
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<code>Content-Length</code> up to the specified maximum amount of
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space. If the maximum buffer space is reached, the buffered
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content is discarded and the attempt to cache is abandoned.</p>
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<note><title>Note:</title>
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<p>Using a nonzero value for <directive>MCacheMaxStreamingBuffer</directive>
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will not delay the transmission of the response to the client.
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As soon as <module>mod_mem_cache</module> copies a block of streamed
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content into a buffer, it sends the block on to the next output
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filter for delivery to the client.</p>
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</note>
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<example>
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# Enable caching of streamed responses up to 64KB:<br />
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MCacheMaxStreamingBuffer 65536
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</example>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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