[erlang-questions] Distributing things

[Joe Armstrong]

On Sat, Nov 7, 2009 at 7:53 PM, Calum <caluml@REDACTED> wrote:
> Hello,
>
> I'm trying to get my head around Erlang, and I've decided to try to
> take an existing program, and distribute it.
> I'm using code from Joe's Erlang book which generates a prime of X
> digits. On my laptop, anything over 500 digits takes a while.
>
> If you have one a single node running the code, it just loops,
> calculates, tests if it's a prime, and increments the number, and
> repeats if it's not a prime.
> It's the "is_prime" test that seems to take the time, so that's the
> part I want to distribute.

Hang on - the algorithm just generates a random integer and tests if
it is a prime,
if it's not a prime it tries again. It has to generate many candidates
before it finds a
prime. Why not start N parallel processes each of which generates and
tests candidates
then when either one of them succeeds you can stop. Sounds easier to me.

/Joe


> I imagine if you have more than one node, you want to kick off "n"
> is_prime tests, but of different values.
>
> What is the best way of going about this? Is it to kick off n, and
> wait for all to return before kicking off another n? This isn't so
> good if one of the nodes takes a very long time to return, as the rest
> are doing nothing.
> Or have a "global" "next value" variable, and each node just gets the
> next one when it's finished its current one?
> What would be the best way of maintaining this "next value" variable?
>
> How can I handle additional nodes "coming on line" as it's running?
> How can I handle a node going offline in the middle of this?
> Would you all just use the existing nodes() nodelist to do this, or
> would you need to extend that in some way?
>
> Is there a good tried and tested method of deciding how to break down
> a large job of 1000000 small jobs into batches for n nodes?
>
>
> Hope these questions makes sense to you,
>
> C
>
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