13,797 research outputs found
RAM-Efficient External Memory Sorting
In recent years a large number of problems have been considered in external
memory models of computation, where the complexity measure is the number of
blocks of data that are moved between slow external memory and fast internal
memory (also called I/Os). In practice, however, internal memory time often
dominates the total running time once I/O-efficiency has been obtained. In this
paper we study algorithms for fundamental problems that are simultaneously
I/O-efficient and internal memory efficient in the RAM model of computation.Comment: To appear in Proceedings of ISAAC 2013, getting the Best Paper Awar
Bidirectional Text Compression in External Memory
Bidirectional compression algorithms work by substituting repeated substrings by references that, unlike in the famous LZ77-scheme, can point to either direction. We present such an algorithm that is particularly suited for an external memory implementation. We evaluate it experimentally on large data sets of size up to 128 GiB (using only 16 GiB of RAM) and show that it is significantly faster than all known LZ77 compressors, while producing a roughly similar number of factors. We also introduce an external memory decompressor for texts compressed with any uni- or bidirectional compression scheme
Lempel-Ziv Parsing in External Memory
For decades, computing the LZ factorization (or LZ77 parsing) of a string has
been a requisite and computationally intensive step in many diverse
applications, including text indexing and data compression. Many algorithms for
LZ77 parsing have been discovered over the years; however, despite the
increasing need to apply LZ77 to massive data sets, no algorithm to date scales
to inputs that exceed the size of internal memory. In this paper we describe
the first algorithm for computing the LZ77 parsing in external memory. Our
algorithm is fast in practice and will allow the next generation of text
indexes to be realised for massive strings and string collections.Comment: 10 page
A Bulk-Parallel Priority Queue in External Memory with STXXL
We propose the design and an implementation of a bulk-parallel external
memory priority queue to take advantage of both shared-memory parallelism and
high external memory transfer speeds to parallel disks. To achieve higher
performance by decoupling item insertions and extractions, we offer two
parallelization interfaces: one using "bulk" sequences, the other by defining
"limit" items. In the design, we discuss how to parallelize insertions using
multiple heaps, and how to calculate a dynamic prediction sequence to prefetch
blocks and apply parallel multiway merge for extraction. Our experimental
results show that in the selected benchmarks the priority queue reaches 75% of
the full parallel I/O bandwidth of rotational disks and and 65% of SSDs, or the
speed of sorting in external memory when bounded by computation.Comment: extended version of SEA'15 conference pape
- …