mod_mem_cache
Content cache keyed to URIs
Experimental
mod_mem_cache.c
mem_cache_module

This module is experimental. Documentation is still under development...

This module requires the service of mod_cache. It acts as a support module for mod_cache and provides a memory based storage manager. mod_mem_cache can be configured to operate in two modes: caching open file descriptors or caching objects in heap storage. mod_mem_cache is most useful when used to cache locally generated content or to cache backend server content for mod_proxy configured for ProxyPass (aka reverse proxy).

Content is stored in and retrieved from the cache using URI based keys. Content with access protection is not cached.

mod_cache
mod_disk_cache
MCacheSize
The maximum amount of memory used by the cache in KBytes
MCacheSize KBytes
MCacheSize 100
server config

The MCacheSize 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 MCacheRemovalAlgorithm.

# Example

MCacheSize 700000

# Note

The MCacheSize value must be greater than the value specified by the MCacheMaxObjectSize directive.

MCacheMaxObjectCount
The maximum number of objects allowed to be placed in the cache
MCacheMaxObjectCount value
MCacheMaxObjectCount 1009
server config

The MCacheMaxObjectCount 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 MCacheRemovalAlgorithm.

# Example

MCacheMaxObjectCount 13001
MCacheMinObjectSize
The minimum size (in bytes) of a document to be allowed in the cache
MCacheMinObjectSize bytes
MCacheMinObjectSize 0
server config

The MCacheMinObjectSize directive sets the minimum size in bytes of a document for it to be considered cacheable.

# Example

MCacheMinObjectSize 10000
MCacheMaxObjectSize
The maximum size (in bytes) of a document allowed in the cache
MCacheMaxObjectSize bytes
MCacheMaxObjectSize 10000
server config

The MCacheMaxObjectSize directive sets the maximum allowable size, in bytes, of a document for it to be considered cacheable.

# Example

MCacheMaxObjectSize 6400000

# Note

The value of MCacheMaxObjectSize must be greater than the value specified by the MCacheMinObjectSize directive.

MCacheRemovalAlgorithm
The algorithm used to select documents for removal from the cache
MCacheRemovalAlgorithm LRU|GDSF
MCacheRemovalAlgorithm GDSF
server config

The MCacheRemovalAlgorithm directive specifies the algorithm used to select documents for removal from the cache. Two choices are available:

`LRU` (Least Recently Used)
  `LRU` removes the documents that have not been accessed for the longest time.
`GDSF` (GreadyDual-Size)
  `GDSF` 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.

# Example

MCacheRemovalAlgorithm GDSF
MCacheRemovalAlgorithm LRU
MCacheMaxStreamingBuffer
Maximum amount of a streamed response to buffer in memory before declaring the response uncacheable
MCacheMaxStreamingBuffer size_in_bytes
MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize
server config

The MCacheMaxStreamingBuffer 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 `Content-Length` may not be known. Sources of streaming responses include proxied responses and the output of CGI scripts. By default, a streamed response will not be cached unless it has a `Content-Length` 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 MCacheMaxStreamingBuffer directive allows buffering of streamed responses that don't contain a `Content-Length` 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.

# Note:

Using a nonzero value for MCacheMaxStreamingBuffer will not delay the transmission of the response to the client. As soon as mod_mem_cache copies a block of streamed content into a buffer, it sends the block on to the next output filter for delivery to the client.

# Enable caching of streamed responses up to 64KB:
MCacheMaxStreamingBuffer 65536