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From "Graham Leggett" <>
Subject Re: Possible new cache architecture
Date Tue, 02 May 2006 15:42:35 GMT
On Tue, May 2, 2006 5:27 pm, Brian Akins said:

> Still not sure how this is different from what we are proposing.  we
> really want to separate protocol from cache stuff.  If we have a
> "revalidate" for the generic cache it should address all your concerns.
> ???

To be HTTP compliant, and to solve thundering herd, we need the following
from a cache:

- The ability to amend a subkey (the headers) on an entry that is already

- The ability to invalidate a particular cached variant (ie headers +
data) in one atomic step, without affecting threads that hold that cached
entry open at the time.

- The ability to read from a cached object that is still being written to.

- A guarantee that the result of a broken write (segfault, timeout,
connection reset by peer, whatever) will not result in a broken cached
entry (ie that the cached entry will eventually be invalidated, and all
threads trying to read from it will eventually get an error).

Certainly separate the protocol from the physical cache, just make sure
the physical cache delivers the shopping list above :)


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