Comparison of external sorting and internal sorting in virtual memory

Abstract

To compare the performance of external sorting and internal sorting in virtual memory, (external) mergesort and (internal) quicksort are performed in corresponding environments. Quicksort is run using a virtual memory with fetch on demand and working set replacement policy. Mergesort uses sublists presorted by replacement selection, double buffering for input and output, and two disks. The performance is measured by main memory space allocation, execution time, and main memory space-time integral. To perform well, quicksort is satisfied with a smaller space allocation than mergesort, and it behaves more consistently with respect to space allocation. Mergesort needs far less execution time than quicksort, mainly because of its efficient overlapping of file handling and processor time. With respect to the space-time integral, quicksort outperforms mergesort only when small files (less than 1000 records) are sorted. With large files, mergesort is better, and the relative difference increases with increasing file size. The optimal page size and window size for quicksort are smaller than those typical to existing virtual memory systems, and they tend to decrease with increasing file size.