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From Graham Leggett <>
Subject Re: Possible new cache architecture
Date Mon, 01 May 2006 19:36:58 GMT
Davi Arnaut wrote:

>> It's a design flaw to create problems that have to be specially coded 
>> around, when you can avoid the problem entirely.
> Maybe I'm missing something, what problems do you foresee ?

There are lots of issues that were uncovered when I split the proxy and 
cache code for httpd v2.0.

A web cache requires two separately alterable cached entities (headers, 
body) just for caching a single variant. This pair of entities need to 
expire and/or be forceably expired (think Cache-Control no-cache) 
atomically. Sure, you can code and debug a lot of code to try and create 
the effect of atomically expiring multiple cache entries at once. Or you 
can avoid this issue entirely by building a generic cache that works 
with key/subkey/data.

There are a number of other issues that have been listed as bugs since 
httpd v1.3 that are still present, most notably the thundering herd 
problem, and the independent caching of variants. There is no point in 
refactoring the cache code if the new code isn't going to be 
significantly better than the existing code.


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