By Topic

Databases in Parallel and Distributed Systems, 1990, Proceedings. Second International Symposium on

Date 2-4 July 1990

Filter Results

Displaying Results 1 - 19 of 19
  • Proceedings. Second International Symposium on Databases in Parallel and Distributed Systems (Cat. No.90CH2895-1)

    Save to Project icon | Request Permissions | PDF file iconPDF (46 KB)  
    Freely Available from IEEE
  • A hierarchical approach to concurrency control for multidatabases

    Page(s): 202 - 210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Hierarchical concurrency control has been proposed as one possible approach for multidatabase systems. However, to apply this approach, some restrictions must be imposed on the local concurrency control algorithms. The restriction is identified. Based on this restriction, the hierarchical concurrency control approach is formalized and its correctness is proven. A novel global concurrency control algorithm based on this hierarchical approach is also presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An experimental performance study of a pipelined recursive query processing strategy

    Page(s): 30 - 43
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    The run-time performance of a strategy (previously proposed by the authors, J. Shao et al., 1989) for processing recursive queries in deductive database system is studied. The algorithm, introduced informally by examples, is coded in occam2 and runs on a network of transputers. A wide range of recursive queries and database structures are used as benchmarks. Both the speedup factors achieved and the elapsed time spent by the strategy in answering recursive queries are analyzed. Experimental results show that it is possible to achieve significant performance improvements when queries are evaluated in parallel. These results provide insights into the success of this strategy in meeting the primary objective of focusing on relevant data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Parallelism in relational data base systems: architectural issues and design approaches

    Page(s): 4 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1732 KB)  

    The issues and solutions relation to intra-query parallelism in a relational DBMS (database management systems) supporting SQL are addressed. A broad framework for the study of the numerous issues that need to be addressed in supporting parallelism efficiently and flexibly is provided. The impact that parallelization of complex queries has on short transactions which have stringent response time constraints is discussed. The advantages and disadvantages of the shared nothing, shared disks and shared everything architectures for parallelism are enumerated. The impact of parallelism on a number of components of an industrial-strength DBMS are pointed out. The different stages of query processing during which parallelism may be gainfully used are identified. The interactions between parallelism and the traditional systems' pipelining technique are analyzed. Finally, the performance implications of parallelizing a specific complex query are studied. This gives a range of sample points for different parameters of a parallel system architecture, namely I/O and communication bandwidth as a function of aggregate MIPS (million instruction per second) View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Parallel handling of integrity constraints on fragmented relations

    Page(s): 138 - 145
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    A short introduction to the important aspects of the PRISMA DBMS (database management system) and to the notation and terminology used is presented. It is shown how integrity constraints formulated in terms of global relations can be translated into a fragmented form. The strategy for constraint enforcement at a conceptual level is discussed. The implementation issues for this strategy are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A transitive closure and magic functions machine

    Page(s): 44 - 54
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    An extended version of the SIMD (single-instruction, multiple-data) relational algebraic processor is presented. In addition to the usual relational and set operations the machine has the ability to recycle its responder sets internally. This allows it to perform repeated joins, for example, without external intervention and so achieve operations such as path discovery and transitive closure in graphs stored as relations and to evaluate various types of recursive query. The many compiled methods for recursive query evaluation are applicable in this system, as in any other relational database, and can be efficiently evaluated because of the in-built recursive and iterative capability of the machine. The magic functions approach has a clear connection with the machine, since it uses relations as magic functions View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Towards an efficient management of objects in a distributed environment

    Page(s): 181 - 190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    A prototype of an object-oriented system implemented in CProlog is described. Its main objective is to demonstrate system features that would support efficient management of objects and object-oriented databases in a persistent and distributed environment. Mechanisms at the low level of the system were considered to support object distribution, mobility control and configuration management in a simple and uniform way. Objects exist in clusters which are transparent to the applications. The prototype is a framework for a self-organizing object-oriented distributed system View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Using join operations as reducers in distributed query processing

    Page(s): 116 - 123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    Semijoin has traditionally been relied upon for reducing the communication cost required for distributed query processing. However, judiciously applying join operations as reducers can lead to further reduction in the communication cost. In view of this fact, the approach of using join operations, in addition to semijoins, as reducers in distributed query processing is explored. It is shown that the problem of determining a sequence of join operations for a query graph can be transformed to that of finding a set of cuts to that graph, where a cut to a graph is a partition of the nodes in that graph. In light of the mapping, an efficient heuristic algorithm to determine an effective sequence of join reducers for a query is developed. The algorithm, using the concept of divide-and-conquer, is shown to have polynomial time complexity. Examples are given to illustrate the results View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Retrieval performance of a distributed text database utilizing a parallel processor document server

    Page(s): 71 - 79
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    Text retrieval systems which store extremely large amounts of text while providing a multiuser retrieval service for a large customer base are discussed. Due to the severe I/O demands of such a system, it is usually beneficial, if not necessary to utilize a multiprocessor system with multiple I/O facilities in an effort to increase the parallel I/O activity, the objective being to lower search response times. The problem is defined, a solution is modeled and it is shown that the application can be handled in a very effective fashion by a multiprocessor system with a simple LAN-based topology. A type of functional splitting which, if done in a careful manner, helps improve search response time is described View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Voting class-an approach to achieving high availability for replicated data

    Page(s): 146 - 156
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    An approach to the design of replica control schemes which can provide higher availability than currently existing voting schemes is proposed. The approach is based on the observation that the existing voting schemes actually belong to a general class, called voting class. This class of voting schemes can be represented in a very simple and uniform way. Thus, a designer can choose the optimal scheme within the voting class by evaluating each of them and choosing the one which maximizes the availability View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Outerjoin optimization in multidatabase systems

    Page(s): 211 - 218
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    Outerjoin is used in distributed relational multidatabase systems for integrating local schemas to a global schema. Queries against the global schema need to be modified, optimized, and decomposed into subqueries at local sites for processing. Since outerjoin combines local relations in different databases to form a global relation, it is expensive to process. Based on the structure of the query and the definition of the schemas, queries with outerjoin, join, select and project operations are optimized. Conditions where outerjoin can be avoided or transformed into a one-sided outerjoin are identified. Considering these conditions makes it possible to reduce the response time for query processing View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multi-join on parallel processors

    Page(s): 92 - 102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    A preliminary evaluation of some multijoin strategies and their performances on parallel hardware is described. The hardware used was a Sequent (under Unix) with 11 usable processors, each with shared and private primary memory. A multijoin was broken down into a series of single joins which were then allocated to clusters, each cluster being a collection of parallel processors. The results of single joins, which were studied by both binary search and hash-merge techniques, were then further processed as necessary. The evaluation was conducted varying a number of parameters, such as cluster size, tuple size and cardinality. The comparative results were plotted. The study highlights the importance of a number of factors that influence the performance of a multijoin operation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficient parallel algorithms for functional dependency manipulations

    Page(s): 126 - 137
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Given a set of functional dependencies Σ and a single dependency σ, it is shown that the algorithm to test whether Σ implies σ is log-space complete in P. The functional dependencies Σ are represented as a directed hypergraph HΣ. A parallel algorithm is presented which solves the above implication problem using P processors on an exclusive-read, exclusive-write parallel random access machine (EREW-PRAM) in O(e/P+n log P) time and on a concurrent-read, concurrent-write PRAM (CRCW-PRAM) in O(e/P+n) time, where e and n are the number of arcs and nodes of the graph HΣ. For graphs HΣ with fixed degree and diameter, it is shown that the closure H Σ+ can be computed in NC. NC algorithms are presented to obtain a nonredundant and a LR-minimum cover for the set of functional dependencies Σ. All the algorithms on an n-node directed hypergraph with fixed degree and diameter can be implemented to run in O(log2 n) time with M(n) processors on a CREW-PRAM model, where M (n) is the cost of multiplying two binary matrices. The algorithms are efficient based on the transitive closure bottleneck phenomenon View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A parallel execution model for a database machine with high performances

    Page(s): 56 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1036 KB)  

    A mixed MIMD/SIMD execution model for a reconfigurable computer is presented. This model is adapted to the use of a specialized associative coprocessor embedded in this host machine. A main characteristic of the model is that it uses four types of processes (decoding, calculus, coprocessor communication and transaction manager) and that in principle one process of each type is allowed on each processor. Time intervals are allocated to operations into partitions of the set of processors. Transfers are usually limited to identifiers, logical addresses and locks. Simulations display a high level of processor occupation. Therefore the machine yield may be very high, and the operations should be fast View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An effective algorithm for parallelizing sort merge joins in the presence of data skew

    Page(s): 103 - 115
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    A parallel sort-merge-join algorithm that uses a divide-and-conquer approach to address the data skew problem is proposed. The algorithm adds an extra scheduling phase to the usual sort, transfer and join phases. During the scheduling phase, a parallelizable optimization algorithm, using the output of the sort phase, attempts to balance the load across the multiple processors in the subsequent join phase. The algorithm naturally identifies the largest skew elements and assigns each of them to an optimal number of processors. Assuming a Zipf-like distribution for data skew, the algorithm is shown to achieve very good load balancing for the join phase in a CPU-bound environment and to be very robust relative to the degree of data skew and the total number of processors View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance evaluation of functional disk system with nonuniform data distribution

    Page(s): 80 - 89
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    The performance of a functional disk system with relational database engine (FDS-RII) for a nonuniform data distribution is analyzed. FDS-RII is a relational storage system, designed to accelerate relational algebraic operations which uses a hash-based algorithm to process relational operations. In the has-based algorithm, a relation is first partitioned into several clusters by a split function. Each cluster is then staged onto the main memory and further, a hash function is applied to each cluster to perform a relational operation. Thus, the nonuniformity of split and hash functions is considered to result from a nonuniform data distribution on the hash-based algorithm. It is possible to attenuate the effect of the hash function nonuniformity by increasing the number of processors and processing the buckets in parallel. In order to address the nonuniformity of split function, the combined hash algorithm is introduced. This algorithm combines the grace hash algorithm with the nested loop algorithm in order to handle the overflown bucket efficiently. Using the combined hash algorithm, it is found that the execution time of the nonuniform data distribution is almost equal to that of the uniform data distribution View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Concepts and methods for the optimization of distributed data processing

    Page(s): 171 - 180
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A model of distributed data processing is introduced and discussed. For this purpose, a typical application system is analyzed and divided into subapplications. To fulfil the task of the global application, the subapplications must communicate in an appropriate manner by exchanging data. In the proposed model the communication between subapplications is split up into two steps: the offering of information by sending subapplications and its acceptance by receiving subapplications. For both communication steps, synchronous and asynchronous processing modes are defined. Supporting those different communication modes, the cooperation between subapplications can be defined very closely to the specific demands of the application system. This optimizes distributed data processing. The prototype implementation of a distributed data management system, based on the flexible communication mechanism described is demonstrated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • JOYCE+: model and language for multi-site distributed systems

    Page(s): 160 - 170
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    The JOYCE+ model for multisite distributed systems is presented and the operational semantic of the asynchronous communication between processes is illustrated with Petri nets. The syntax of the JOYCE+ language is presented in terms of the Guarded Commands language. The expressive power of the JOYCE+ language in distributed synchronization problems with timeout handling is illustrated through examples. Software development environments (based on JOYCE+) for distributed systems over multi- and monoprocess computer networks are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Correcting execution of distributed queries

    Page(s): 192 - 201
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    A low overhead delay method for deciding when to correct a strategy is presented. Sampling is used to estimate the size relations and alternative heuristic strategies prepared in a background mode are used to decide when to correct. Correction is made only if lower overall delay is achieved, including correction time. Evaluation using a model of a distributed database indicates that the heuristic strategies are near optimal. Moreover, it suggests that it is usually correct to abort creation of an intermediate relation which is much larger than predicted View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.