CORES: Towards Scan-Optimized Columnar Storage for Nested Records

The relatively high cost of record deserialization is increasingly becoming the bottleneck of column-based storage systems in tree-structured applications [58]. Due to record transformation in the storage layer, unnecessary processing costs derived from fields and rows irrelevant to queries may be very heavy in nested schemas, significantly wasting the computational resources in large-scale analytical workloads. This leads to the question of how to reduce both the deserialization and IO costs of queries with highly selective filters following arbitrary paths in a nested schema.

We present CORES (Column-Oriented Regeneration Embedding Scheme) to push highly selective filters down into column-based storage engines, where each filter consists of several filtering conditions on a field. By applying highly selective filters in the storage layer, we demonstrate that both the deserialization and IO costs could be significantly reduced. We show how to introduce fine-grained composition on filtering results. We generalize this technique by two pair-wise operations, rollup and drilldown, such that a series of conjunctive filters can effectively deliver their payloads in nested schema. The proposed methods are implemented on an open-source platform. For practical purposes, we highlight how to build a column storage engine and how to drive a query efficiently based on a cost model. We apply this design to the nested relational model especially when hierarchical entities are frequently required by ad hoc queries. The experiments, including a real workload and the modified TPCH benchmark, demonstrate that CORES improves the performance by 0.7×--26.9× compared to state-of-the-art platforms in scan-intensive workloads.