Elastic Scaling of Stateful Operators Over Fluctuating Data Streams

Elastic scaling of parallel operators has emerged as a powerful approach to reduce response time in stream applications with fluctuating inputs. Many state-of-the-art works focus on stateless operators and change the operator parallelism from one aspect. They often lack efficient management of operator states and overlook the costs associated with resource over-provisioning. To overcome these limitations, we introduce Es-Stream for elastic scaling of stateful operators over fluctuating data streams, which includes: 1) We observe that under-provisioning of operator parallelism leads to data pile-up, resulting in longer system latency, while over-provisioning of operator parallelism causes idle instances and additional resource consumption. 2) The Es-Stream system scales in two dimensions: the parallelism of operators and the number of resources. It dynamically adjusts operators to an optimal parallelism while scaling the resources used by the stream application. 3) When the parallelism of stateful operators changes, upstream operators backup downstream operators' state and cache the emitted data tuples at dynamic time intervals, ensuring the operator parallelism is adjusted in a low-overhead way. 4) Experimental results demonstrate that Es-Stream provides promising performance improvements, reducing the maximum system latency by 3x and saving the maximum state recovery time by 2x, compared to existing state-of-the-art works.