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Algebraic optimization of recursive queries
, 1992
"... Over the past few years, much attention has been paid to deductive databases. They offer a logicbased interface, and allow formulation of complex recursive queries. However, they do not offer appropriate update facilities, and do not support existing applications. To overcome these problems an SQL ..."
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Cited by 11 (4 self)
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Over the past few years, much attention has been paid to deductive databases. They offer a logicbased interface, and allow formulation of complex recursive queries. However, they do not offer appropriate update facilities, and do not support existing applications. To overcome these problems an SQLlike interface is required besides a logicbased interface. In the PRISMA project we have developed a tightlycoupled distributed database, on a multiprocessor machine, with two user interfaces: SQL and PRISMAIog. Query optimization is localized in one component: the relational query optimizer. Therefore, we have defined an eXtended Relational Algebra that allows recursive query formulation and can also be used for expressing executable schedules, and we have developed algebraic optimization strategies for recursive queries. In this paper we describe an optimization strategy that rewrites regular (in the context of formal grammars) mutually recursive queries into standard Relational Algebra and transitive closure operations. We also describe how to push selections into the resulting transitive closure operations. The reason we focus on algebraic optimization is that, in our opinion, the new generation of advanced database systems will be built starting from existing stateoftheart relational technology, instead of building a completely new class of systems.
Data Fragmentation for Parallel Transitive Closure Strategies
 In Proceedings of the IEEE 9th International Conference on Data Engineering
, 1993
"... A topic that is currently inspiring a lot of research is parallel (distributed) computation of transitive closure queries. In [10] the disconnection set approach has been introduced as an effective strategy for such a computation. It involves reformulating a transitive closure query on a relation in ..."
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Cited by 9 (1 self)
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A topic that is currently inspiring a lot of research is parallel (distributed) computation of transitive closure queries. In [10] the disconnection set approach has been introduced as an effective strategy for such a computation. It involves reformulating a transitive closure query on a relation into a number of transitive closure queries on smaller fragments; these queries can then execute independently on the fragments, without need for communication and without computing the same tuples at more than one processor. Now that effective strategies as just mentioned have been developed, the next problem is that of developing adequate data fragmentation strategies for these approaches. This is a difficult problem, but of paramount importance to the success of these approaches. We discuss the issues that influence data fragmentation. We present a number of algorithms, each focusing on one of the important issues. We discuss the pros and cons of the algorithms, and we give some results of ...
Implementation and performance evaluation of a parallel transitive closure algorithm on PRISMA/DB
, 1993
"... This paper describes an experimental performance study of the parallel computation of transitive closure operations on a parallel database system. This work brings two research efforts together. The first is the development of an efficient execution strategy for the parallel computation of path prob ..."
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Cited by 8 (4 self)
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This paper describes an experimental performance study of the parallel computation of transitive closure operations on a parallel database system. This work brings two research efforts together. The first is the development of an efficient execution strategy for the parallel computation of path problems, called the Disconnection Set Approach. The second is the development and implementation of a parallel, mainmemory DBMS, called PRISMA/DB. Here, we report on the implementation of the disconnection set approach on PRISMA/DB, showing how the latter's design allowed us to easily extend the functionality of the system. It is shown that the parallel implementation of the disconnection set approach yields good performance characteristics, and that linear speedup with respect to a special purpose single processor algorithm is achieved. Finally, we describe a number of experiments that show to what extent data fragmentation issues influence the performance of the disconnection set approach. 1...
Parallel Hierarchical Evaluation of Transitive Closure Queries
, 1991
"... This paper presents a new approach to parallel computation of transitive closure queries using a semantic data fragmentation. We assume that tuples of a large base relation denote edges in a graph, which models a transportation network; we propose a fragmentation algorithm which produces the partiti ..."
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Cited by 7 (5 self)
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This paper presents a new approach to parallel computation of transitive closure queries using a semantic data fragmentation. We assume that tuples of a large base relation denote edges in a graph, which models a transportation network; we propose a fragmentation algorithm which produces the partitioning of the base relation into several fragments such that any fragment corresponds to a subgraph. Any two fragments are considered as either adjacent or nonadjacent; two fragments are adjacent when the corresponding subgraphs have a nonempty intersection. One fragment, called highspeed fragment, collects all edges which guarantee maximum speed, these edges correspond to highways or to highspeed intercity trains. Thus, the fragmentation algorithm induces a hierarchical relationship between the highspeed fragment and all other fragments. With this fragmentation, any query about paths connecting two nodes can be answered by using just the fragments in which nodes are located and the high...
An Experimental Study on Transitive Closure Representations
"... We present two new compact transitive closure representations. The first uses intervals and the second chains to store the closure. Both representations are based on previous methods designed for acyclic graphs. The new representations are applicable to all kinds of graphs, and can be efficiently co ..."
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Cited by 1 (0 self)
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We present two new compact transitive closure representations. The first uses intervals and the second chains to store the closure. Both representations are based on previous methods designed for acyclic graphs. The new representations are applicable to all kinds of graphs, and can be efficiently constructed during a single traversal of the input graph. We compared experimentally the average size of these representations and traditional list based representations. The inputs were random graphs. The interval representation outperformed the other representations: it typically required a space at most linear to the number of vertices of the input graph. The chain representation did not save much space compared to a list representation. We also studied the complexity of constructing the interval representation. Our results indicate that in the models of random graphs that we used, the transitive closure can typically be computed in a time linear to the size of the input graph when the interv...
Transitive closure algorithm DISK_TC and its performance analysis
"... We present a new algorithm for computing the full transitive closure of a binary relation. We analyze its averagecase performance experimentally in an environment where secondary memory (disk) must be used to store the data. We compare our new algorithm, called disk tc, with the algorithm btc desi ..."
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We present a new algorithm for computing the full transitive closure of a binary relation. We analyze its averagecase performance experimentally in an environment where secondary memory (disk) must be used to store the data. We compare our new algorithm, called disk tc, with the algorithm btc designed by Ionnadis et al. [26] and reported by them to be the most efficient algorithm in disk memory environment. We present both quantitative and qualitative results showing that disk tc is faster than btc. In our analysis, we simulate the disk I/O in the main memory. Simulation takes less time than measuring a real system that does actual disk I/O; thus we can study a large number of inputs. We present also our analysis method and tools, which are applicable to other algorithm performance studies. Copyright c fl Vesa Hirvisalo, Esko Nuutila, and Eljas SoisalonSoininen. All rights reserved. TKOB135 ISBN 951223386X ISSN 12396893 TKK OFFSET 1 1 Introduction This paper presents a new...
Optimization Strategies for Parallel Linear Recursive Query Processing
, 1995
"... Query optimization for sequential execution of nonrecursive queries has reached a high level of sophistication in commercial DBMS. The successful application of parallel processing for the evaluation of recursive queries will require a query optimizer of comparable sophistication. The groundwork fo ..."
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Query optimization for sequential execution of nonrecursive queries has reached a high level of sophistication in commercial DBMS. The successful application of parallel processing for the evaluation of recursive queries will require a query optimizer of comparable sophistication. The groundwork for creating this new breed of query optimizer will consist of a combination of theoretical insight and empirical investigation. Restricting our attention to linear recursive queries, we illustrate this process by developing a family of query processing strategies and, through experiments on a parallel computer, obtaining the basic information needed for an optimizer's heuristics. 1 Introduction Query optimizers for commercial DBMSs are very sophisticated in their ability to find reasonably efficient execution plans for nonrecursive queries computed on a uniprocessor. In such queries, the cost of performing the joins dominates the total cost and the optimizer must choose (a) an order in whi...