Concurrency control

About: Concurrency control is a research topic. Over the lifetime, 5112 publications have been published within this topic receiving 107438 citations.

Some Deadlock Properties of Computer Systems

Abstract: Several examples of deadlock occurring in present day computer systems are given Next, there is a discussion of the strategms which can be ~sed to deal with the deadlock problem A theory of computer systems is developed so that the terms "process" and "deadlock" can be defined. "Reusable resources" are introduced to model objects that are shared among processes, and "consumable resources" are introduced to model signals or messages passed among processes. Then a rumple graph model of computer systems m developed, and its deadlock propertms are investigated This graph model unifies a number of previous results, leads to efficient deadlock detection and prevenUon algorithms, and ~s useful for teaching purposes.

Concurrency Control and Consistency of Multiple Copies of Data in Distributed INGRES.

Abstract: This paper contains algorithms for ensuring the consistency of a distributed relational data base subject to multiple, concurrent updates. Also included are mechanisms to correctly update multiple copies of objects and to continue operation when less than all machines in the network are operational. Together with [4] and [12], this paper constitutes the significant portions of the design for a distributed data base version of INGRES.

Stochastic Models of Computer Communication Systems

Abstract: (Read before the Royal Statistical Society at a meeting organized by the Research Section on Wednesday, May 8th, 1985, Professor J. B. Copas in the Chair) SUMMARY This paper describes some examples of the stochastic models found useful in the design and analysis of advanced computer and communication systems. Our major theme might be termed the control of contention. As illustrations of this theme we discuss concurrency control procedures for databases, dynamic channel assignment for cellular radio, and random access schemes for the control of a broadcast channel. We emphasize asymptotic properties of product-form distributions and we present some new results on the stability of acknowledgement based random access schemes. This paper is intended to describe to the Society some examples of the stochastic models found useful in the design and analysis of advanced computer and communication systems. The examples chosen are broadly concerned with what might be termed the control of contention, and an attempt has been made to provide enough of the technical background to motivate the models considered. In Section 2 we describe a probabilistic model, due to Mitra (1985), for conflicts anlong tran- sactions in a database. Such conflicts can arise in distributed computer systems, where to ensure the consistency of a database it is often necessary to forbid the concurrent execution of transactions involving common items: a transaction must then contend with other transactions for access to the items it requires. Mitra (1985) has shown that his model can be used to answer some important design questions concerning concurrency control procedures which use exclusive and non-exclusive locks. Mitra's results are based upon a product-form solution; we indicate how his asymptotic formulae can be extended beyond the range of light traffic and the assumption of an unstructured database. In Section 3 we discuss one of the many interesting problems which arise in connection with cellular radio. Cellular radio makes efficient use of a limited number of radio channels by allowing the repeated reuse of each channel in sufficiently separated spatial regions. The topic we consider is contention between different regions for the use of dynamically assigned channels. Everitt and Macfadyen (1983) have described an analytically tractable method of dynamic channel assign- ment, which they term the maximum packing strategy. Again a product form solution is involved: from this it is easy to obtain asymptotic formulae applicable in light traffic. These formulae establish the advantage of the strategy over a fixed channel assignment for low enough loss pro- babilities, but the advantage disappears as traffic and the number of channels increase. The real potential of dynamic schemes is their ability to cope automatically with traffic intensities which fluctuate in space and time.

System level concurrency control for distributed database systems

Abstract: A distributed database system is one in which the database is spread among several sites and application programs “move” from site to site to access and update the data they need. The concurrency control is that portion of the system that responds to the read and write requests of the application programs. Its job is to maintain the global consistency of the distributed database while ensuring that the termination of the application programs is not prevented by phenomena such as deadlock. We assume each individual site has its own local concurrency control which responds to requests at that site and can only communicate with concurrency controls at other sites when an application program moves from site to site, terminates, or aborts.This paper presents designs for several distributed concurrency controls and demonstrates that they work correctly. It also investigates some of the implications of global consistency of a distributed database and discusses phenomena that can prevent termination of application programs.

Making snapshot isolation serializable

Abstract: Snapshot Isolation (SI) is a multiversion concurrency control algorithm, first described in Berenson et al. [1995]. SI is attractive because it provides an isolation level that avoids many of the common concurrency anomalies, and has been implemented by Oracle and Microsoft SQL Server (with certain minor variations). SI does not guarantee serializability in all cases, but the TPC-C benchmark application [TPC-C], for example, executes under SI without serialization anomalies. All major database system products are delivered with default nonserializable isolation levels, often ones that encounter serialization anomalies more commonly than SI, and we suspect that numerous isolation errors occur each day at many large sites because of this, leading to corrupt data sometimes noted in data warehouse applications. The classical justification for lower isolation levels is that applications can be run under such levels to improve efficiency when they can be shown not to result in serious errors, but little or no guidance has been offered to application programmers and DBAs by vendors as to how to avoid such errors. This article develops a theory that characterizes when nonserializable executions of applications can occur under SI. Near the end of the article, we apply this theory to demonstrate that the TPC-C benchmark application has no serialization anomalies under SI, and then discuss how this demonstration can be generalized to other applications. We also present a discussion on how to modify the program logic of applications that are nonserializable under SI so that serializability will be guaranteed.