On Tuesday 10 April 2007 23:17, Ramon Diaz-Uriarte wrote:

> Of course, you are right there. I think that might still be the case.
> At the time we made our decision, and decided to go for MPI, MPI 2 was
> already out, and MPI seemed "more like the current/future standard"
> than PVM.

That's always been the case. In fact MPI is a standard, where as PVM always
was an implementation defining a so-called standard.

> So using papply with Rmpi requires sharper programmers than using
> snow? Hey, it is good to know I am that smarter. I'll wear that as a
> badge :-).

You are!  I've never been patient enough to use plain Rmpi or rpvm except a
few times, but for me, the advantage of snow is that you get all the
backends, not just MPI. In fact, I've heard mention that some folks are
sticking together a NWS backend as well.

> Anyway, papply (with Rmpi) is not, in my experience, any harder than
> snow (with either rpvm or Rmpi). In fact, I find papply a lot simpler
> than snow (clusterApply and clusterApplyLB). For one thing, debugging
> is very simple, since papply becomes lapply if no lam universe is
> booted.

In fact it might be easier, since we never put together decent aggregation
routines.

(smarter doesn't mean works harder, just more intelligently :-).

> I see, though, that I might want to check PVM just for the sake of the
> fault tolerance in snowFT.

Fault tolerance is one of those very ill-defined words.  Specifically:

#1 - mapping pRNG streams to work units, not just CPUs or dispatch order (both
of which can differ), for reproducibility

#2 - handling "failure to complete" on worker nodes gracefully.

However, you'd need checkpointing or probably a miracle to handle failure on
the master...


best,
-tony

blindglobe@(protected)
Muttenz, Switzerland.
"Commit early,commit often, and commit in a repository from which we can
easily
roll-back your mistakes" (AJR, 4Jan05).

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