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<modulesynopsis metafile="mod_mem_cache.xml.meta">

<name>mod_mem_cache</name>

<description>Content cache keyed to URIs</description>

<status>Experimental</status>

<sourcefile>mod_mem_cache.c</sourcefile>

<identifier>mem_cache_module</identifier>

<summary>

<note type="warning">

This module is experimental. Documentation is still under

development...

</note>

<p>This module <em>requires</em> the service of <module

>mod_cache</module>. It acts as a support module for <module

>mod_cache</module> and provides a memory based storage manager.

<module>mod_mem_cache</module> can be configured to operate in two

modes: caching open file descriptors or caching objects in heap storage.

<module>mod_mem_cache</module> is most useful when used to cache locally

generated content or to cache backend server content for <module

>mod_proxy</module> configured for <directive module="mod_proxy"

>ProxyPass</directive> (aka <dfn>reverse proxy</dfn>).</p>

<p>Content is stored in and retrieved from the cache using URI based

keys. Content with access protection is not cached.</p>

</summary>

<seealso><module>mod_cache</module></seealso>

<seealso><module>mod_disk_cache</module></seealso>

<directivesynopsis>

<name>MCacheSize</name>

<description>The maximum amount of memory used by the cache in

KBytes</description>

<syntax>MCacheSize <var>KBytes</var></syntax>

<default>MCacheSize 100</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MCacheSize</directive> directive sets the maximum

amount of memory to be used by the cache, in KBytes (1024-byte units).

If a new object needs to be inserted in the cache and the size of the

object is greater than the remaining memory, objects will be removed

until the new object can be cached. The object to be removed is

selected using the algorithm specified by <directive

module="mod_mem_cache">MCacheRemovalAlgorithm</directive>.</p>

<example><title>Example</title>

MCacheSize 700000

</example>

<note><title>Note</title>

<p>The <directive>MCacheSize</directive> value must be greater than

the value specified by the <directive module="mod_mem_cache"

>MCacheMaxObjectSize</directive> directive.</p>

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MCacheMaxObjectCount</name>

<description>The maximum number of objects allowed to be placed in the

cache</description>

<syntax>MCacheMaxObjectCount <var>value</var></syntax>

<default>MCacheMaxObjectCount 1009</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MCacheMaxObjectCount</directive> directive sets the

maximum number of objects to be cached. The value is used to create the

open hash table. If a new object needs to be inserted in the cache and

the maximum number of objects has been reached, an object will be

removed to allow the new object to be cached. The object to be removed

is selected using the algorithm specified by <directive

module="mod_mem_cache">MCacheRemovalAlgorithm</directive>.</p>

<example><title>Example</title>

MCacheMaxObjectCount 13001

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MCacheMinObjectSize</name>

<description>The minimum size (in bytes) of a document to be allowed in the

cache</description>

<syntax>MCacheMinObjectSize <var>bytes</var></syntax>

<default>MCacheMinObjectSize 0</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MCacheMinObjectSize</directive> directive sets the

minimum size in bytes of a document for it to be considered

cacheable.</p>

<example><title>Example</title>

MCacheMinObjectSize 10000

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MCacheMaxObjectSize</name>

<description>The maximum size (in bytes) of a document allowed in the

cache</description>

<syntax>MCacheMaxObjectSize <var>bytes</var></syntax>

<default>MCacheMaxObjectSize 10000</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MCacheMaxObjectSize</directive> directive sets the

maximum allowable size, in bytes, of a document for it to be considered

cacheable.</p>

<example><title>Example</title>

MCacheMaxObjectSize 6400000

</example>

<note><title>Note</title>

<p>The value of <directive>MCacheMaxObjectSize</directive> must be

greater than the value specified by the <directive

module="mod_mem_cache">MCacheMinObjectSize</directive> directive.</p>

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MCacheRemovalAlgorithm</name>

<description>The algorithm used to select documents for removal from the

cache</description>

<syntax>MCacheRemovalAlgorithm LRU|GDSF</syntax>

<default>MCacheRemovalAlgorithm GDSF</default>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MCacheRemovalAlgorithm</directive> directive specifies

the algorithm used to select documents for removal from the cache.

Two choices are available:</p>

<dl>

<dt><code>LRU</code> (Least Recently Used)</dt>

<dd><code>LRU</code> removes the documents that have not been accessed

for the longest time.</dd>

<dt><code>GDSF</code> (GreadyDual-Size)</dt>

<dd><code>GDSF</code> assigns a priority to cached documents based

on the cost of a cache miss and the size of the document. Documents

with the lowest priority are removed first.</dd>

</dl>

<example><title>Example</title>

MCacheRemovalAlgorithm GDSF<br />

MCacheRemovalAlgorithm LRU

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MCacheMaxStreamingBuffer</name>

<description>Maximum amount of a streamed response to buffer in memory

before declaring the response uncacheable</description>

<syntax>MCacheMaxStreamingBuffer <var>size_in_bytes</var></syntax>

<default>MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize</default>

<contextlist><context>server config</context>

</contextlist>

<usage>

<p>The <directive>MCacheMaxStreamingBuffer</directive> directive

specifies the maximum number of bytes of a streamed response to

buffer before deciding that the response is too big to cache.

A streamed response is one in which the entire content is not

immediately available and in which the <code>Content-Length</code>

may not be known. Sources of streaming responses include proxied

responses and the output of CGI scripts. By default, a streamed

response will <em>not</em> be cached unless it has a

<code>Content-Length</code> header. The reason for this is to

avoid using a large amount of memory to buffer a partial response

that might end up being too large to fit in the cache.

The <directive>MCacheMaxStreamingBuffer</directive> directive allows

buffering of streamed responses that don't contain a

<code>Content-Length</code> up to the specified maximum amount of

space. If the maximum buffer space is reached, the buffered

content is discarded and the attempt to cache is abandoned.</p>

<note><title>Note:</title>

<p>Using a nonzero value for <directive>MCacheMaxStreamingBuffer</directive>

will not delay the transmission of the response to the client.

As soon as <module>mod_mem_cache</module> copies a block of streamed

content into a buffer, it sends the block on to the next output

filter for delivery to the client.</p>

</note>

<example>

# Enable caching of streamed responses up to 64KB:<br />

MCacheMaxStreamingBuffer 65536

</example>

</usage>

</directivesynopsis>

</modulesynopsis>