During scale testing, it was noticed that tuning the size of the accumulated row batches in data stream sender will affect the performance of Impala. This is understandable as a larger row batch will amortize the cost of compression and RPC in general. The default value is 16KB per channel. Experiment in a 38 node cluster with 48 concurrent users running 10TB TPC-DS shows about 5% improvement in query-per-hour when bumping the default value to 512KB. This is a tradeoff between memory consumption and performance. Having this flag allows us to tune for performance more easily.