Optimization of data flow execution in a parallel environment

Although the modern data flows are executed in parallel and distributed environments, e.g. on a multi-core machine or on the cloud, current cost models, e.g., those considered by state-of-the-art data flow optimization techniques, do not accurately reflect the response time of real data flow execution in these execution environments. This is mainly due to the fact that the impact of parallelism, and more specifically, the impact of concurrent task execution on the running time is not adequately modeled in current cost models. The contribution of this work is twofold. Firstly, we propose an advanced cost model that aims to reflect the response time of a data flow that is executed in parallel more accurately. Secondly, we show that existing optimization solutions are inadequate and develop new optimization techniques targeting the proposed cost model. We focus on the single multi-core machine environment provided by modern business intelligence tools, such as Pentaho Kettle, but our approach can be extended to massively parallel and distributed settings. The distinctive features of our proposal is that we model both time overlaps and the impact of concurrency on task running times in a combined manner; the latter is appropriately quantified and its significance is exemplified. Furthermore, we propose extensions to current optimizers that decide on the exact ordering of flow tasks taking into account the new optimization metric. Finally, we evaluate the new optimization algorithms and show up to 59% response time improvement over state-of-the-art task ordering techniques.