1. A computer implemented method for load balancing using progressive sampling to achieve a load balancing quality target over a plurality of worker tasks at a target confidence level, the method comprising: computing a maximum workload variance target based on the load balancing quality target and the target confidence level; sampling, by a computer, a first set of sampled input records to be assigned to at least two of the worker tasks; forming a prospective load balancing assignment by assigning the first set of sampled input records to the plurality of worker tasks based on a workload estimate for the worker tasks; determining whether an additional number of input records are required be sampled to achieve the load balancing target; and sampling the additional number of input records.