Showing papers on "Concurrency control published in 1980"

Experience with processes and monitors in Mesa

Abstract: The use of monitors for describing concurrency has been much discussed in the literature. When monitors are used in real systems of any size, however, a number of problems arise which have not been adequately dealt with: the semantics of nested monitor calls; the various ways of defining the meaning of WAIT; priority scheduling; handling of timeouts, aborts and other exceptional conditions; interactions with process creation and destruction; monitoring large numbers of small objects. These problems are addressed by the facilities described here for concurrent programming in Mesa. Experience with several substantial applications gives us some confidence in the validity of our solutions.

Introduction to a system for distributed databases (SDD-1)

Abstract: The declining cost of computer hardware and the increasing data processing needs of geographically dispersed organizations have led to substantial interest in distributed data management. SDD-1 is a distributed database management system currently being developed by Computer Corporation of America. Users interact with SDD-1 precisely as if it were a nondistributed database system because SDD-1 handles all issues arising from the distribution of data. These issues include distributed concurrency control, distributed query processing, resiliency to component failure, and distributed directory management. This paper presents an overview of the SDD-1 design and its solutions to the above problems.This paper is the first of a series of companion papers on SDD-1 (Bernstein and Shipman [2], Bernstein et al. [4], and Hammer and Shipman [14]).

Concurrency control in a system for distributed databases (SDD-1)

Abstract: This paper presents the concurrency control strategy of SDD-1. SDD-1, a System for Distributed Databases, is a prototype distributed database system being developed by Computer Corporation of America. In SDD-1, portions of data distributed throughout a network may be replicated at multiple sites. The SDD-1 concurrency control guarantees database consistency in the face of such distribution and replication.This paper is one of a series of companion papers on SDD-1 [4, 10, 12, 21].

Concurrent manipulation of binary search trees

Abstract: The concurrent manipulation of a binary search tree is considered in this paper. The systems presented can support any number of concurrent processes which perform searching, insertion, deletion, and rotation (reorganization) on the tree, but allow any process to lock only a constant number of nodes at any time. Also, in the systems, searches are essentially never blocked. The concurrency control techniques introduced in the paper include the use of special nodes and pointers to redirect searches, and the use of copies of sections of the tree to introduce many changes simultaneously and therefore avoid unpredictable interleaving. Methods developed in this paper may provide new insights into other problems in the area of concurrent database manipulation.

Timestamp-based algorithms for concurrency control in distributed database systems

Abstract: We decompose the problem of concurrency control into the sub-problems of read-write and write-write synchronization. We present a series of timestamp- based algorithms (called synchronization techniques) that achieve read-write and/or write-write synchronization. And we show how to combine any read-write technique with any write-write technique to yield a complete concurrency control algorithm (called a method). Using this framework we describe 12 "principal" concurrency control methods in detail. Each principal method can be modified by refinements described in the paper, leading to more than 50 distinct concurrency control algorithms.

Reliability mechanisms for SDD-1: a system for distributed databases

Abstract: This paper presents the reliability mechanisms of SDD-1, a prototype distributed database system being developed by the Computer Corporation of America. Reliability algorithms in SDD-1 center around the concept of the Reliable Network (RelNet). The RelNet is a communications medium incorporating facilities for site status monitoring, event timestamping, multiply buffered message delivery, and the atomic control of distributed transactions.This paper is one of a series of companion papers on SDD-1 [3, 4, 6, 13].

A Transaction Model

Abstract: This paper is an attempt to tersely restate several theoretical results about transaction recovery and concurrency control. A formal model of entities, actions, transactions, entity failures, concurrency and distributed system is required to present these results. Included are theorems on transaction undo and redo, degrees of consistency, predicate locks, granularity of locks, deadlock, and two-phase commit.

On Deadlock Detection in Distributed Systems

Abstract: A hierarchically organized and a distributed protocol for deadlock detection in distributed databases are presented in [1]. In this paper we show that the distributed protocol is incorrect, and present possible remedies. However, the distributed protocol remains impractical because "condensations" of "transaction-wait-for" graphs make graph updates difficult to perform. Delayed graph updates cause the occurrence of false deadlocks in this as well as in some other deadlock detection protocols for distributed systems. The performance degradation that results from false deadlocks depends on the characteristics of each protocol.

The Deadlock Problem: An Overview

Abstract: Deadlock is a constant threat in terminal-oriented systems. This comprehensive study of deadlock-handling techniques introduces a method for on-line detection in distributed data bases.

Optimal Design of Distributed Information Systems

Abstract: In this paper a model is developed for the optimization of distributed information systems. Compared with the previous work in this area, the model is more complete, since it considers simultaneously the distribution of processing power, the allocation of programs and databases, and the assignment of communication line capacities. It also considers the return flow of information, as well as the dependencies between programs and databases. In addition, an algorithm, based on the "bounded branch and bound" integer programming technique, has been developed to obtain the optimal solution of the model. The algorithm is more efficient than several existing general nonlinear integer programming algorithms. Also, it avoids some of the disadvantages of heuristic and decomposition algorithms which are used widely in the optimization of computer networks and distributed databases. The algorithm has been implemented in Fortran, and the computation times of the algorithm for several test problems have been found very reasonable.

The correctness of concurrency control mechanisms in a system for distributed databases (SDD-1)

Abstract: This paper presents a formal analysis of the concurrency control strategy of SDD-1. SDD-1, a System for Distributed Databases, is a prototype distributed database system being developed by Computer Corporation of America. In SDD-1, portions of data distributed throughout a network may be replicated at multiple sites. The SDD-1 concurrency control guarantees database consistency in the face of such distribution and replication.This paper is one of a series of companion papers on SDD-1 [2, 8].

The Distributed Double-Loop Computer Network (DDLCN)

Abstract: This paper presents the design of the Distributed Double-Loop Computer Network (DDLCN), which is a local-area distributed computing system that interconnects midi, mini and micro computers using a fault-tolerant double-loop network. Several new features and novel concepts have been incorporated into the design of its subsystems, viz., the reliable communication network, the programming/operating system (P/OS), and the distributed loop data base system (DLDBS). The interface design is unique in that it employs tri-state control logic and bit-sliced processing, thereby enabling the network to become dynamically reconfigurable and fault tolerant with respect to communication link failure as well as component failure in the interface. Three classes of multi-destination communication protocols, each providing a different degree of reliability, have been incorporated into the network to facilitate efficient and reliable exchanges of messages.The P/OS is distinguished from other similar research efforts in that its ultimate goal is to support not only communication and cooperation among autonomous, distributed processes running at various nodes, but also to support convenient and correct resource sharing through program generation (semi-automatic programming) for application and systems programmers. A new concurrency control mechanism for DLDBS has been developed, which uses distributed control without global locking and is deadlock free. In addition to being simple to implement and having good performance (high throughput and low delay), the mechanism is also robust with respect to failure of both communication links and hosts.

A Distributed Control Algorithm for Reliably and Consistently Updating Replicated Databases

Abstract: This paper presents a deadlock-free and distributed control algorithm for robustly and consistently updating replicated databases. This algorithm is based on local locking and time stamps on lock tables which permit detection of conflicts among transactions executed at different sites. Messages are exchanged in the network whenever a transaction commitment occurs, that is, at the end of every consistent step of local processing. Conflicts among remote transactions are resolved by a roll back procedure. Local restart is based on a journal of locks which provides backup facilities. Performance in terms of the number of messages and volume of control messages of the proposed algorithm is compared with that of the voting and centralized locking algorithms. These results reveal that the proposed distributed control algorithm performs, in most cases, comparably to the centralized locking algorithm and better than the voting algorithm.

Detection Of Deadlocks In Distributed Database Systems

Abstract: Designers of DBMS have faced many problems with concurrent access and update of information V/hen a database is distributed over several dissimilar computer systems, such problems as detection and avoidance of process deadlock are compounded Additional communications may be necessary between the computers to determine the relationships between the data resources and processesIn this paper a thorough discussion of the drawbacks of, and the problems iavolved in, previous proposals to handle deadlocks in distributed DBMS is provided Earlier algorithms have required substantial communication and coordination between computers should a deadlock arise, thus delaying corrective action The concept of "on-line" deadlock detection is introduced here; using a graph-theoretic model to represent the process interactions, a new algorithm for the immediate detection of deadlocks in distributed databases is proposed The theorems upon which our algorithms are based are presented without formal proof A tutor

The analysis of the effects of concurrency control on distributed database system performance

Abstract: In this paper we review the recent results on the impact of concurrency control (CC) on distributed database system (DDBS). Then we introduce a classification for CC mechanisms. Finally we qualitatively analyse the dependencies among DDBS system, CC and workload (or application) parameters and their impact on DDBS performance. The purpose of such analysis is to provide an understanding of DDBS design problems and to explain recent and seemingly contradictory results on the effect of CC on DDBS performance.

Distributed data base management: Some thoughts and analyses

Abstract: The new decade will witness the widespread usage of distributed processing systems. Distributed data base management will turn out to be one of the important applications of this relatively new technology. This paper initially presents a brief outline of the nature of research that has been performed so far in this area. Next, it discusses some of the important issues (like integrity and security constraints, deadlocks, concurrency control, etc.) and analyses some proposed mechanisms. Performance and correctness issues are also addressed. Then, a brief sketch of an adaptive architecture for distributed data base management systems is presented. The last section lists some future directions for research in this area.

Technical papers detection of deadlocks in distributed database systems

Abstract: Designers of DBMS have faced many problems with concurrent access and update of information. V/hen a database is distributed over several dissimilar computer systems, such problems as detection and avoidance of process deadlock are compounded. Additional communications may be necessary between the computers to determine the relationships between the data resources and processes. In this paper a thorough discussion of the drawbacks of, and the problems iavolved in, previous proposals to handle deadlocks in distributed DBMS is provided. Earlier algorithms have required substantial communication and coordination betv^een computers should a deadlock arise, thus delaying corrective action. The concept of "on-line" deadlock detection is introduced here; using a graph-theoreti c model to represent the process interactions, a new algorithm for the immediate detection of deadlocks in distributed databases is proposed. The theorems upon which our algorithms are based are presented without formal proof. A tutorial approach is taken and application of the theorems is illustrated through a set of examples. Several highlights of our proposals are emphasized.