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Ben Ricker wrote:
> I am pitching Jserv against iPlanet tomorrow and I had one more
> question. iPlanet claims to have multi-processor support built in (I
> thought the OS handeled that). I wanted to get something clear: what
> support does Apache/Jserv provide for multip processor machines?
>
> I thought I read somewhere that Apache is not multip processor aware. Is
> this true?
Yes, multiprocessor support on Apache/JServ depends on the OS you're using.
We use Linux, so that is what I can talk about. In Linux, the granularity of
load-balancing between processors is a process. That means that, if you have
some heavy computation going on, better divide it between two or more
processes, so that the OS can load-balance them.
For JServ: JVMs come in two flavors -- native and green threads. With native
threads, the scheduling between threads is done by the OS. As for Linux,
that means, for the most part, different processes (yes, I know the facts
about threads on Linux, but for comparison purposes we can ignore that
because the kernel divides the load among threads between the various
processors). Green threads, on the other hand, use the JVM's scheduler,
which may or may not provide a more suitable solution. When you use native
threads, you to worry, for example, about your system's maximum processes
number. Green threads, on the other hand, tend to slow things down quite a
bit under heavy load with code that is I/O bound, because the whole JVM
blocks for I/O instead of a single thread/process. Also, on multiprocessors,
green threads do you no good unless you have many JServ instances running
(for example, you can use JServ's load-balancing facilities between
processors on a single machine when using green threads). That said, we have
found -- and these are empirical results, no serious research done whatsover
-- that green threads tend to be more stable, at least for our applications.
> Any information to make these issues clearer would help me.
Hope the above was of any use.
> Ben Ricker
> Web Administrator
> US-Rx, Inc.
Ulisses Montenegro
Systems Administrator/RADIX
http://www.radix.com.br/
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