Using logarithmic code-expansion to speedup index access and maintenance

Abstract

In this paper we have studied the performance of alternative representations of binary search-trees for indexing a relation kept in main-memory. It was shown that space/time performance of the common techniques, such as sorted heaps, and more complex data structures, such as avl-trees, can be improved considerably. In particular, when an upperbound is determined during program construction on the maximal size of the indices, an efficient mapping, called the virtual tree, from binary search tree to array exists. The resulting search structure ensures an upperbound on the number of comparisons for searching and maintenance will only start to deteriorate when the area set aside for holding the index is nearly full. In addition, we showed that limiting the maximal size of the index structure permits judicious use of code-expansion, i.e. logarithmic code expansion, to further improve the performance of the algorithms. For a search dominant environment our approach is better than the more space consumptive binary trees representations based on pointer chasing. In a volatile environment the space/time performance can be controlled precisely.