Improving speculative query execution support by the use of the hypergraph representation

Abstract

Speculative support for query execution in Relational Database Management Systems (RDBMSs) based on a graph-analytic approach is the subject of this paper. Optimized speculative queries are defined by analyzing graph representations of a stream of input queries arriving to a RDBMS. The analysis is permanently performed based on a Speculation Window moving on the RDBMS input query queue. The proposed optimization concerns both the definition of the speculative queries to be executed and the methods of speculative query results assignment to incoming input queries. The paper shows how to design RDBMS query execution speculative support using two kinds of the query graph representations: the query multigraphs and the query hypergraphs. In particular, the paper proposes an improvement of the use of the speculative query results defined based on the query multigraph analysis by an additional assignment to queries in an extension of the Speculation Window in the input query queue. The additional assignment is based on the analysis of the speculative and user input queries represented jointly in a common hypergraph. Two approaches to the proposed speculative results improvement are discussed which increase the speculative result life time. The properties of the speculative query execution support based on the mentioned query graph representations and algorithmic approaches have been assessed by the experiments with the simulated execution of the query testbed sets based on the popular TPC-H benchmark.