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Documents authored by Khan, Jamshed

Document
DOI: 10.4230/LIPIcs.WABI.2023.16
Fast, Parallel, and Cache-Friendly Suffix Array Construction

Authors: Jamshed Khan, Tobias Rubel, Laxman Dhulipala, Erin Molloy, and Rob Patro

Published in: LIPIcs, Volume 273, 23rd International Workshop on Algorithms in Bioinformatics (WABI 2023)

Abstract
String indexes such as the suffix array (SA) and the closely related longest common prefix (LCP) array are fundamental objects in bioinformatics and have a wide variety of applications. Despite their importance in practice, few scalable parallel algorithms for constructing these are known, and the existing algorithms can be highly non-trivial to implement and parallelize. In this paper we present CaPS-SA, a simple and scalable parallel algorithm for constructing these string indexes inspired by samplesort. Due to its design, CaPS-SA has excellent memory-locality and thus incurs fewer cache misses and achieves strong performance on modern multicore systems with deep cache hierarchies. We show that despite its simple design, CaPS-SA outperforms existing state-of-the-art parallel SA and LCP-array construction algorithms on modern hardware. Finally, motivated by applications in modern aligners where the query strings have bounded lengths, we introduce the notion of a bounded-context SA and show that CaPS-SA can easily be extended to exploit this structure to obtain further speedups.
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Jamshed Khan, Tobias Rubel, Laxman Dhulipala, Erin Molloy, and Rob Patro. Fast, Parallel, and Cache-Friendly Suffix Array Construction. In 23rd International Workshop on Algorithms in Bioinformatics (WABI 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 273, pp. 16:1-16:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{khan_et_al:LIPIcs.WABI.2023.16,
  author =	{Khan, Jamshed and Rubel, Tobias and Dhulipala, Laxman and Molloy, Erin and Patro, Rob},
  title =	{{Fast, Parallel, and Cache-Friendly Suffix Array Construction}},
  booktitle =	{23rd International Workshop on Algorithms in Bioinformatics (WABI 2023)},
  pages =	{16:1--16:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-294-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{273},
  editor =	{Belazzougui, Djamal and Ouangraoua, A\"{i}da},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2023.16},
  URN =		{urn:nbn:de:0030-drops-186424},
  doi =		{10.4230/LIPIcs.WABI.2023.16},
  annote =	{Keywords: Suffix Array, Longest Common Prefix, Data Structures, Indexing, Parallel Algorithms}
}
Document
DOI: 10.4230/LIPIcs.WABI.2023.18
Fulgor: A Fast and Compact {k-mer} Index for Large-Scale Matching and Color Queries

Authors: Jason Fan, Noor Pratap Singh, Jamshed Khan, Giulio Ermanno Pibiri, and Rob Patro

Published in: LIPIcs, Volume 273, 23rd International Workshop on Algorithms in Bioinformatics (WABI 2023)

Abstract
The problem of sequence identification or matching - determining the subset of reference sequences from a given collection that are likely to contain a short, queried nucleotide sequence - is relevant for many important tasks in Computational Biology, such as metagenomics and pan-genome analysis. Due to the complex nature of such analyses and the large scale of the reference collections a resource-efficient solution to this problem is of utmost importance. This poses the threefold challenge of representing the reference collection with a data structure that is efficient to query, has light memory usage, and scales well to large collections. To solve this problem, we describe how recent advancements in associative, order-preserving, k-mer dictionaries can be combined with a compressed inverted index to implement a fast and compact colored de Bruijn graph data structure. This index takes full advantage of the fact that unitigs in the colored de Bruijn graph are monochromatic (all k-mers in a unitig have the same set of references of origin, or "color"), leveraging the order-preserving property of its dictionary. In fact, k-mers are kept in unitig order by the dictionary, thereby allowing for the encoding of the map from k-mers to their inverted lists in as little as 1+o(1) bits per unitig. Hence, one inverted list per unitig is stored in the index with almost no space/time overhead. By combining this property with simple but effective compression methods for inverted lists, the index achieves very small space. We implement these methods in a tool called Fulgor. Compared to Themisto, the prior state of the art, Fulgor indexes a heterogeneous collection of 30,691 bacterial genomes in 3.8× less space, a collection of 150,000 Salmonella enterica genomes in approximately 2× less space, is at least twice as fast for color queries, and is 2-6 × faster to construct.
Cite as

Jason Fan, Noor Pratap Singh, Jamshed Khan, Giulio Ermanno Pibiri, and Rob Patro. Fulgor: A Fast and Compact {k-mer} Index for Large-Scale Matching and Color Queries. In 23rd International Workshop on Algorithms in Bioinformatics (WABI 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 273, pp. 18:1-18:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{fan_et_al:LIPIcs.WABI.2023.18,
  author =	{Fan, Jason and Singh, Noor Pratap and Khan, Jamshed and Pibiri, Giulio Ermanno and Patro, Rob},
  title =	{{Fulgor: A Fast and Compact \{k-mer\} Index for Large-Scale Matching and Color Queries}},
  booktitle =	{23rd International Workshop on Algorithms in Bioinformatics (WABI 2023)},
  pages =	{18:1--18:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-294-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{273},
  editor =	{Belazzougui, Djamal and Ouangraoua, A\"{i}da},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2023.18},
  URN =		{urn:nbn:de:0030-drops-186446},
  doi =		{10.4230/LIPIcs.WABI.2023.18},
  annote =	{Keywords: k-mers, Colored de Bruijn Graph, Compression, Read-mapping}
}
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