A web-site-based partitioning technique for reducing preprocessing overhead of parallel PageRank computation

A power method formulation, which efficiently handles the problem of dangling pages, is investigated for parallelization of PageRank computation. Hypergraph-partitioning-based sparse matrix partitioning methods can be successfully used for efficient parallelization. However, the preprocessing overhead due to hypergraph partitioning, which must be repeated often due to the evolving nature of the Web, is quite significant compared to the duration of the PageRank computation. To alleviate this problem, we utilize the information that sites form a natural clustering on pages to propose a site-based hypergraph-partitioning technique, which does not degrade the quality of the parallelization. We also propose an efficient parallelization scheme for matrix-vector multiplies in order to avoid possible communication due to the pages without in-links. Experimental results on realistic datasets validate the effectiveness of the proposed models. © Springer-Verlag Berlin Heidelberg 2007

Site-Based Partitioning and Repartitioning Techniques for Parallel PageRank Computation

Cataloged from PDF version of article.The PageRank algorithm is an important component in effective web search. At the core of this algorithm are repeated sparse matrix-vector multiplications where the involved web matrices grow in parallel with the growth of the web and are stored in a distributed manner due to space limitations. Hence, the PageRank computation, which is frequently repeated, must be performed in parallel with high-efficiency and low-preprocessing overhead while considering the initial distributed nature of the web matrices. Our contributions in this work are twofold. We first investigate the application of state-of-the-art sparse matrix partitioning models in order to attain high efficiency in parallel PageRank computations with a particular focus on reducing the preprocessing overhead they introduce. For this purpose, we evaluate two different compression schemes on the web matrix using the site information inherently available in links. Second, we consider the more realistic scenario of starting with an initially distributed data and extend our algorithms to cover the repartitioning of such data for efficient PageRank computation. We report performance results using our parallelization of a state-of-the-art PageRank algorithm on two different PC clusters with 40 and 64 processors. Experiments show that the proposed techniques achieve considerably high speedups while incurring a preprocessing overhead of several iterations (for some instances even less than a single iteration) of the underlying sequential PageRank algorithm. © 2011 IEEE

Web-site-based partitioning techniques for efficient parallelization of the PageRank computation

Cataloged from PDF version of article.Web search engines use ranking techniques to order Web pages in query results. PageRank is an important technique, which orders Web pages according to the linkage structure of the Web. The efficiency of the PageRank computation is important since the constantly evolving nature of the Web requires this computation to be repeated many times. PageRank computation includes repeated iterative sparse matrix-vector multiplications. Due to the enormous size of the Web matrix to be multiplied, PageRank computations are usually carried out on parallel systems. However, efficiently parallelizing PageRank is not an easy task, because of the irregular sparsity pattern of the Web matrix. Graph and hypergraphpartitioning-based techniques are widely used for efficiently parallelizing matrixvector multiplications. Recently, a hypergraph-partitioning-based decomposition technique for fast parallel computation of PageRank is proposed. This technique aims to minimize the communication overhead of the parallel matrix-vector multiplication. However, the proposed technique has a high prepropocessing time, which makes the technique impractical. In this work, we propose 1D (rowwise and columnwise) and 2D (fine-grain and checkerboard) decomposition models using web-site-based graph and hypergraph-partitioning techniques. Proposed models minimize the communication overhead of the parallel PageRank computations with a reasonable preprocessing time. The models encapsulate not only the matrix-vector multiplication, but the overall iterative algorithm. Conducted experiments show that the proposed models achieve fast PageRank computation with low preprocessing time, compared with those in the literature.Cevahir, AliM.S

Efficient External-Memory Algorithms for Graph Mining

The explosion of big data in areas like the web and social networks has posed big challenges to research activities, including data mining, information retrieval, security etc. This dissertation focuses on a particular area, graph mining, and specifically proposes several novel algorithms to solve the problems of triangle listing and computation of neighborhood function in large-scale graphs. We first study the classic problem of triangle listing. We generalize the existing in-memory algorithms into a single framework of 18 triangle-search techniques. We then develop a novel external-memory approach, which we call Pruned Companion Files (PCF), that supports disk operation of all 18 algorithms. When compared to state-of-the-art available implementations MGT and PDTL, PCF runs 5-10 times faster and exhibits orders of magnitude less I/O. We next focus on I/O complexity of triangle listing. Recent work by Pagh etc. provides an appealing theoretical I/O complexity for triangle listing via graph partitioning by random coloring of nodes. Since no implementation of Pagh is available and little is known about the comparison between Pagh and PCF, we carefully implement Pagh, undertake an investigation into the properties of these algorithms, model their I/O cost, understand their shortcomings, and shed light on the conditions under which each method defeats the other. This insight leads us to develop a novel framework we call Trigon that surpasses the I/O performance of both techniques in all graphs and under all RAM conditions. We finally turn our attention to neighborhood function. Exact computation of neighborhood function is expensive in terms of CPU and I/O cost. Previous work mostly focuses on approximations. We show that our novel techniques developed for triangle listing can also be applied to this problem. We next study an application of neighborhood function to ranking of Internet hosts. Our method computes neighborhood functions for each host as an indication of its reputation. The evaluation shows that our method is robust to ranking manipulation and brings less spam to its top ranking list compared to PageRank and TrustRank

Asynchronous iterative solution for dominant eigenvectors with applications in performance modelling and PageRank

Imperial Users onl

Efficient External-Memory Algorithms for Graph Mining

The explosion of big data in areas like the web and social networks has posed big challenges to research activities, including data mining, information retrieval, security etc. This dissertation focuses on a particular area, graph mining, and specifically proposes several novel algorithms to solve the problems of triangle listing and computation of neighborhood function in large-scale graphs. We first study the classic problem of triangle listing. We generalize the existing in-memory algorithms into a single framework of 18 triangle-search techniques. We then develop a novel external-memory approach, which we call Pruned Companion Files (PCF), that supports disk operation of all 18 algorithms. When compared to state-of-the-art available implementations MGT and PDTL, PCF runs 5-10 times faster and exhibits orders of magnitude less I/O. We next focus on I/O complexity of triangle listing. Recent work by Pagh etc. provides an appealing theoretical I/O complexity for triangle listing via graph partitioning by random coloring of nodes. Since no implementation of Pagh is available and little is known about the comparison between Pagh and PCF, we carefully implement Pagh, undertake an investigation into the properties of these algorithms, model their I/O cost, understand their shortcomings, and shed light on the conditions under which each method defeats the other. This insight leads us to develop a novel framework we call Trigon that surpasses the I/O performance of both techniques in all graphs and under all RAM conditions. We finally turn our attention to neighborhood function. Exact computation of neighborhood function is expensive in terms of CPU and I/O cost. Previous work mostly focuses on approximations. We show that our novel techniques developed for triangle listing can also be applied to this problem. We next study an application of neighborhood function to ranking of Internet hosts. Our method computes neighborhood functions for each host as an indication of its reputation. The evaluation shows that our method is robust to ranking manipulation and brings less spam to its top ranking list compared to PageRank and TrustRank

Algorithms and Software for the Analysis of Large Complex Networks

The work presented intersects three main areas, namely graph algorithmics, network science and applied software engineering. Each computational method discussed relates to one of the main tasks of data analysis: to extract structural features from network data, such as methods for community detection; or to transform network data, such as methods to sparsify a network and reduce its size while keeping essential properties; or to realistically model networks through generative models

Reducing the Overhead of Memory Space, Network Communication and Disk I/O for Analytic Frameworks in Big Data Ecosystem

To facilitate big data processing, many distributed analytic frameworks and storage systems such as Apache Hadoop, Apache Hama, Apache Spark and Hadoop Distributed File System (HDFS) have been developed. Currently, many researchers are conducting research to either make them more scalable or enabling them to support more analysis applications. In my PhD study, I conducted three main works in this topic, which are minimizing the communication delay in Apache Hama, minimizing the memory space and computational overhead in HDFS and minimizing the disk I/O overhead for approximation applications in Hadoop ecosystem. Specifically, In Apache Hama, communication delay makes up a large percentage of the overall graph processing time. While most recent research has focused on reducing the number of network messages, we add a runtime communication and computation scheduler to overlap them as much as possible. As a result, communication delay can be mitigated. In HDFS, the block location table and its corresponding maintenance could occupy more than half of the memory space and 30% of processing capacity in master node, which severely limit the scalability and performance of master node. We propose Deister that uses deterministic mathematical calculations to eliminate the huge table for storing the block locations and its corresponding maintenance. My third work proposes to enable both efficient and accurate approximations on arbitrary sub-datasets of a large dataset. Existing offline sampling based approximation systems are not adaptive to dynamic query workloads and online sampling based approximation systems suffer from low I/O efficiency and poor estimation accuracy. Therefore, we develop a distribution aware method called Sapprox. Our idea is to collect the occurrences of a sub-dataset at each logical partition of a dataset (storage distribution) in the distributed system at a very small cost, and make good use of such information to facilitate online sampling