Scalable in situ scientific data encoding for analytical query processing

The process of scientific data analysis in high-performance computing environments has been evolving along with the advancement of computing capabilities. With the onset of exascale computing, the increasing gap between compute performance and I/O bandwidth has rendered the traditional method of post-simulation processing a tedious process. Despite the challenges due to increased data production, there exists an opportunity to benefit from "cheap" computing power to perform query-driven exploration and visualization during simulation time. To accelerate such analyses, applications traditionally augment raw data with large indexes, post-simulation, which are then repeatedly utilized for data exploration. However, the generation of current state-of-the-art indexes involve a compute- and memory-intensive processing, thus rendering them inapplicable in an in situ context. In this paper we propose DIRAQ, a parallel in situ, in network data encoding and reorganization technique that enables the transformation of simulation output into a query-efficient form, with negligible runtime overhead to the simulation run. DIRAQ begins with an effective core-local, precision-based encoding approach, which incorporates an embedded compressed index that is 3 -- 6x smaller than current state-of-the-art indexing schemes. DIRAQ then applies an in network index merging strategy, enabling the creation of aggregated indexes ideally suited for spatial-context querying that speed up query responses by up to 10x versus alternative techniques. We also employ a novel aggregation strategy that is topology-, data-, and memory-aware, resulting in efficient I/O and yielding overall end-to-end encoding and I/O time that is less than that required to write the raw data with MPI collective I/O.