Represents the desired parallelism of an SMB read operation. For a given set of sources, targetParallelism can be set to any number between the least and greatest numbers of buckets among sources. This can be dynamically configured using TargetParallelism#min() or TargetParallelism#max(), which at graph construction time will determine the least or greatest amount of parallelism based on sources. Alternately, TargetParallelism#of(int) can be used to statically configure a custom value, or TargetParallelism#auto() can be used to let the runner decide how to split the SMB read at runtime based on the combined byte size of the inputs.

If no value is specified, SMB read operations will use Auto parallelism.

When selecting a target parallelism for your SMB operation, there are tradeoffs to consider:

- Minimal parallelism means a fewer number of workers merging data from potentially many buckets. For example, if source A has 4 buckets and source B has 64, a minimally parallel SMB read would have 4 workers, each one merging 1 bucket from source A and 16 buckets from source B. This read may have low throughput. - Maximal parallelism means that each bucket is read by at least one worker. For example, if source A has 4 buckets and source B has 64, a maximally parallel SMB read would have 64 workers, each one merging 1 bucket from source B and 1 bucket from source A, replicated 16 times. This may have better throughput than the minimal example, but more expensive because every key group from the replicated sources must be re-hashed to avoid emitting duplicate records. - A custom parallelism in the middle of these bounds may be the best balance of speed and computing cost.