Which is the right degree of parallism?

[Timo Walther]

Hey everyone,

I want to get the maximum performance of my small 2 node cluster. At the 
moment my execution plan has a "parallelism" of "1" at each operator.
What "-p XX" argument should I pass to the job? The number of nodes, 
number of CPUs or number of slots?

Thanks and regards,
Timo