Abstract: Parallel data processing may include map and reduce processes. Map processes may include at least one input thread and at least one output thread. Input threads may apply map operations to produce key/value pairs from input data blocks. These pairs may be sent to internal shuffle units which distribute the pairs, sending specific pairs to particular output threads. Output threads may include multiblock accumulators to accumulate and/or multiblock combiners to combine values associated with common keys in the key/value pairs. Output threads can output intermediate pairs of keys and combined values. Likewise, reduce processes may access intermediate key/value pairs using multiple input threads. Reduce operations may be applied to the combined values associated with each key. Reduce processes may contain internal shuffle units that distributes key/value pairs and sends specific pairs to particular output threads. These threads then produce the final output.