Open-Source Databases: Within, Outside, or Beyond Lehman’s Laws of Software Evolution?

Abstract. Lehman’s laws of software evolution is a well-established set of observations (matured during the last forty years) on how the typical software systems evolve. However, the applicability of these laws on databases has not been studied so far. To this end, we have performed a thorough, large-scale study on the evolution of databases that are part of larger open source projects, publicly available through open source repositories, and report on the validity of the laws on the grounds of properties like size, growth, and amount of change per version

The Worst Page-Replacement Policy

Abstract. In this paper, we consider the question: what is the worst possible page-replacement strategy? Our goal is to devise an online strategy that has the highest possible fraction of misses as compared to the worst offline strategy. We show that there is no deterministic, online pagereplacement strategy that is competitive with the worst offline strategy. We give a randomized strategy based on the “most-recently-used ” heuristic, and show that this is the worst possible online page-replacement strategy.

SIMD Vectorization of Straight Line FFT Code

Abstract. This paper presents compiler technology that targets general purpose microprocessors augmented with SIMD execution units for exploiting data level parallelism. FFT kernels are accelerated by automatically vectorizing blocks of straight line code for processors featuring two-way short vector SIMD extensions like AMD’s 3DNow! and Intel’s SSE 2. Additionally, a special compiler backend is introduced which is able to (i) utilize particular code properties, (ii) generate optimized address computation, and (iii) apply specialized register allocation and instruction scheduling. Experiments show that automatic SIMD vectorization can achieve performance that is comparable to the optimal hand-generated code for FFT kernels. The newly developed methods have been integrated into the codelet generator of Fftw and successfully vectorized complicated code like real-to-halfcomplex non-power-of-two FFT kernels. The floatingpoint performance of Fftw’s scalar version has been more than doubled, resulting in the fastest FFT implementation to date.