1) There's no way to configure minimum number of tasks per groom server at
this moment. Let's assume that there're 20 nodes (groom servers) and
bsp.tasks.maximum is 5. So total task slots are 100. If my job requires only
10 tasks, the tasks can be executed on from 2 to 10 nodes.
If you want to spread tasks widely across cluster, you need to see https://issues.apache.org/jira/browse/HAMA-900
2) Each task runs in a different JVM. And yes, they runs in synchronous
parallel fashion, based on message-passing.
Best Regards, Edward J. Yoon