Flexible user query order for the speculative query support in RDBMS

This paper concerns speculative query execution support for RDBMS based on the dynamic analysis of input (user) query stream. A middleware called the Speculative Layer is presented. Based on a specific multigraph representation of groups of consecutive input queries, called the Speculation Window, the Speculative Layer generates speculative queries for look-ahead execution. These speculatively obtained results are then used while executing user queries. This paper shortly presents the structure of the Speculative Layer and the adopted graph modelling method. Then, a new strategy of queries in the Speculation Window is introduced. Depending on the availability of executed speculative queries results we allow order of user queries in the Speculation Window changes. If a user query was to be executed without the speculative support, we prefer to delay its execution in favour of one of the consecutive user queries, expecting that speculative results obtained in the nearest future will by useful for the delayed query. The experimental results presented in a multithreaded environment, cooperating with a SQLite database, show that the proposed strategy reduces the number of user queries executed without the speculative results. Additional series of experiments verifies that the certain parameters describing the speculative support system, like Speculation Window size, are properly chosen.