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From Stefano Mazzocchi <stef...@apache.org>
Subject Accessing cache validities from flow
Date Tue, 16 Dec 2003 08:52:16 GMT
After lots of thinking, I came to the conclusion that the only way of 
doing serious caching is using the "inverted cache" approach, which is 
prototyped in the "eventcache" block.

My problem is that linotype is too slow for the load that my blog 
generates and runs at 98% of server CPU. The reason for this is that 
very little caching is performed. I could pregenerate the pages and let 
them served static, but that would prevent me from playing with 
run-time data like the referring request headers.

Now, the core of linotype is the following pipeline:

  1) scans the directories that hold the news
  2) includes them
  3) filters them

as you can easily see, the approach is totally wrong: filtering should 
happen *before* the inclusion... the problem is that since the file 
system is such a stupid repository, metadata is included in the files, 
so I have to include them before I can filter them.

The use of a serious repository and a serious query language on top of 
the metadata will solve that issue and allow to scale a few orders of 
magnitue more in terms of requests, which will keep me happy for a 
while.

But still, thinking a little bigger than my own blog, the ideal 
solution would be to avoid querying entirely if there is no need to.

Now, the way the event cache works is like this:

  a) a cache validity is generated
  b) pipeline is executed
  c) result is stored in the cache

then the pipeline is never called, until an event is triggered 
externally (from an avalon component) that invalidates that particular 
cache entity.

Now, the problem is: if I am not the one who generates the validity (in 
linotype, it's the directory generator), how can I invalidate it? how 
can I have access to it?

I'm starting to think that the cocoon cache needs a serious redesign to 
deal with these issues... and this scares me :-( but it's *waay* too 
important to let go.

Thoughts?

--
Stefano.


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