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From Niklas Edmundsson <>
Subject Re: Possible new cache architecture
Date Tue, 02 May 2006 12:18:30 GMT
On Tue, 2 May 2006, Graham Leggett wrote:

>>> This is great, in doing this you've been solving a proxy bug that was
>>> first reported in 1998 :).
>> This already works in the case you get the data from the proxy backend. It
>> does
>> not work for local files that get cached (the scenario Niklas uses the
>> cache
>> for).
> Ok then I have misunderstood - I was referring to the thundering herd
> problem.

Exactly what is the thundering herd problem? I can guess the general 
problem, but without a more precise definition I can't really say if 
my patch fixes it or not.

If it's:
* Link to latest GNOME Live CD gets published on Slashdot.
* A gazillion users click the link to download it.
* mod_disk_cache starts a new instance of caching the file for each
   request, until someone has completed caching the file.

Then this patch solves the problem regardless of whether it's a static 
file or dynamically generated content since it only allows one 
instance to cache the file (OK, there's a small hole so there can be 
multiple instances but it's waaaay smaller than now), all other 
instances delivers data as the caching process is writing it.

Additionally, if it's a static file that's allowed to be cached in 
the background it solves:
* Reduce chance of user getting bored since the data is delivered
   while being cached.
* The user got bored and closed the connection so the painfully cached
   file gets deleted.

  Niklas Edmundsson, Admin @ {acc,hpc2n}      |
  Illiterate?  Write for information!

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