On May 19, 2006, at 3:00 PM, Rick Morrison wrote:
But I've read story after story about the evils of thread-based
systems
failing in strange ways under load.
probably because they dont synchronize shared resources
properly....it took a very long time for me to get Myghty to be able
to reload, recompile and memory-manage components in midstream, as
well as read and update the various cache backends, without cracking
up under load tests. "ab -c 50" is your friend.
I think I understand that
best-practices for for threaded Paste apps is to leave the global
namespace alone, and start and complete a single request in a single
thread -- "finish what you start". Is that really sufficient for
creating reliable multi-threaded apps under load?
single request per single thread...this is how every threaded web
application server ive ever seen *except* for twisted does it.
However, that doesnt mean the thread dies after the request (Python's
built-in ThreadingMixIn for use with BaseHTTPServer does do it that
way, but also doesnt scale). usually there is a fixed set of
"worker" threads started up which handle request after request. if
load gets high, then the pool of threads grows temporarily.
this is why I tend to like using something like mod_python with
Apache; you get the benefits of your Python program being managed by
Apache's very mature and widely used process model (although on unix
its usually a forking model and not a threading one).
although i hear Lighthttpd is the bomb too, and i just checked http://
www.bittorrent.com/ which serves millions of hits a day using Myghty
and its actually using lighthttpd, which uses a threaded model.
Or is there perhaps
some other concurrency mechanism that will work with SA that we've
missed?
SA is not in the business of concurrency mechanisms at all. the
connection pool has a real basic system built upon Queue.Queue, and
everything else which is stateful and mutable-in-session (i.e. not a
Mapper object which is configurational and isnt expected to change
after initial configuration) is unique to the current thread.
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