Shared index scans for data warehouses

Abstract

In this paper we propose a new “transcurrent execution model” (TEM) for concurrent user queries against tree indexes. Our model exploits intra-parallelism of the index scan and dynamically de- composes each query into a set of disjoint “query patches”. TEM integrates the ideas of prefetching and shared scans in a new framework, suit- able for dynamic multi-user environments. It supports time constraints in the scheduling of these patches and introduces the notion of data flow for achieving a steady progress of all queries. Our experiments demonstrate that the transcurrent query execution results in high locality of I/O which in turn translates to performance benefits in terms of query execution time, buffer hit ratio and disk throughput. These benefits increase as the workload in the warehouse increases and offer a scalable solution to the I/O problem of data warehouses.