Doug Cutting wrote:
>Kelvin Tan wrote:
fetcher as a series of event queues (ala SEDA) instead
of with threads.
I have never been able to write a async version of things with Java's
nio that outperforms a threaded version. In theory it is possible,
since you can avoid thread switching overheads. But in practice I have
found it difficult.
I read the David Culler, et al SEDA paper a while back and I think
the real benefit is twofold: (1) more concurrent connectionsand
(2) graceful degradation (meaning fair scheduling) at maximum load.
IIRC, they hint at competitive-with-apache web serving, but this
depends on specific mix of requests/file sizes, etc.; Tomcat can
also beat the apache web server under some conditions.
Services that need to maintain lots of mostly-idle connections
(like instant messaging) benefit the most from a SEDA architecture.
It should be possible to have graceful degradation with a
thread-oriented architecture. Perhaps a self-tuning procedure
that, for a specific installation, could discover the parameter
settings to get the most out of a server and have it refuse requests
that would push it into the unfair scheduling zone.
Paul
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