setChunkSize: Set the default granularity of distributed tasks.
Description
A job is the collection of all tasks in a foreach loop.
A task is a collection of loop iterations of at most size chunkSize.
R workers are assigned work by task in blocks of at most
chunkSize loop iterations per task.
The default value is one iteration per task.
Setting the default chunk size larger for shorter-running jobs can
substantially improve performance. Setting this value too high can
negatively impact load-balancing across workers, however.