Parallel External Memory Suffix Sorting

Abstract

Suffix sorting (or suffix array construction) is one of the most important tasks in string processing, with dozens of applications, particularly in text indexing and data compression. Some of these applications require the suffix array to be built for large inputs that greatly exceed the size of RAM and so external memory must be used. However, existing approaches for external memory suffix sorting either use debilitatingly large amounts of disk space, or become too slow when the size of the input data is more than a few times bigger than the size of RAM. In this paper we address the latter problem via a non-trivial parallelization of computation. In our experiments, the resulting algorithm is much faster than the best prior external memory algorithms while using very little disk space in addition to what is needed for the input and output. On the way to this result we provide the current fastest (parallel) internal memory algorithm for suffix sorting, which is usually around twice as fast as previous methods, while using around one quarter of the working space.