Elasticity

As described in the preceding section, the number of desired partitions of each operator that is likely to be a bottleneck can be specified as part of the application configuration and the platform will ensure that the desired partitions are created at application start time. However, this is not possible when the volume of data flows can fluctuate unpredictably since we cannot forecast the number of required partitions.

The platform has the required elasticity to support such scenarios via dynamic scaling: the application writer can implement the Partitioner interface along with the related StatsListener interface, either directly in the operator or in a separate object that is set on the operator as an attribute. These interfaces allow the operator to periodically examine current metrics such as throughput, latency, or even custom metrics, and, based on those values, create new partitions or remove existing partitions, or both. All the resource allocation and deallocation is...