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From Brian Akins <>
Subject Possible new cache architecture
Date Thu, 27 Apr 2006 14:04:19 GMT
The components:
mod_http_cache: what mod_cache is currently
mod_cache: a generic caching module - provides glue between providers 
and other modules.  Think mod_dbd...
cache providers: disk, mem, memcache, mysql, etc.

An example mod_http_cache:

-generate cache key
-ask mod_cache for object with key
-mod_cache checks provider(s) and returns object on "hit"
-object may contain vary info, regenerate key and ask mod_cache with new 
key (this would be equivalent to header)
-ask mod_cache for the body
-serve data to client

This would remove all the HTTP specific stuff from the cache providers 
and Vary could be handled in a central location (mod_http_cache).  And 
it *should* be fairly trivial to write and stack cache providers.

Some functions a provider should provide:
init(args...) - initialize an instance :)
open(instance, key) - open a cache object
read_buffer(object, buffer, copy) - read entire object into buffer. 
buffer may be read only (ie, it may be mmapped or part of sql statement) 
or make it a copy.
read_bb(object, brigade, copy) - read object into a brigade. copy if 
flag is set
store_bb(object, brigade) - store a bucket brigade
store_buffer(object, buffer) - store a blob of data

Thoughts?  I'm sure we may need more/better cache provider functions.

Brian Akins
Lead Systems Engineer
CNN Internet Technologies

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