On Jun 28, 2006, at 4:03 PM, Bryan Sant wrote:
On 6/28/06, Hans Fugal <[EMAIL PROTECTED]> wrote:
I'm also not very good at enterprise-level performance testing/
thinking,
but I'll venture that insofar as rails is not hindered by the ruby
threads implementation it's by working around the limitations.
What are
the limitations, exactly? In my mind the primary problem is that
if you
block a thread in certain ways, you block the whole process. Aside
from
that, a virtual thread isn't all that different from a real
thread, and
if your program is a primary contender for resources you will
probably
not notice much detriment due to scheduling.
Maybe Stuart or someone else has more insight into this than I do. If
not, I can ask the URUG people or maybe the ruby-talk list, I suspect
someone there would have a better answer.
Your application will get zero benefit from multiple CPUs/cores if you
don't use real threads. On a single CPU (and single core) system,
this doesn't matter much (as you've described).
That's only true if you limit yourself to a single instance of your
application, which would be a rather silly thing to do in the case of
web programming. If you design your application such that requests
can be handled transparently by multiple instances of your
application, not only do you get to scale across the CPUs in a single
machine, but you can also scale across multiple machines!
And while we talk about scaling, you might want to look at how a
system using OS threads compares to one using "green" threads as the
number of threads rises. OS threads have a pretty serious memory
overhead and context switching delay, and highly multithreaded
programs tend to break down much faster under load with OS threads
than "green" threads. This can be worked around to some degree, of
course, with constructs like thread pools, but at cost of the
complexity of the program.
Certainly there are advantages and disadvantages to either thread
implementation (as there are to using threads as opposed to other
concurrency mechanisms), and it's better to know about them and make
informed decisions than to just use OS Threads because that's what
everyone else seems to say is best.
--Levi
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