Arvola Chan

The implementation of an integrated concurrency control and recovery scheme

This paper describes the implementation level design of an integrated concurrency control and recovery scheme based on the maintenance of multiple versions of data objects in a database. The concurrency control mechanism enhances parallelism by eliminating interference between retrieval and update transactions. The recovery mechanism permits efficient transaction and system recovery by keeping before-images of data objects at the page (block) level. This paper addresses the key technical problems in the implementation of such an integrated scheme. We present an efficient garbage collection algorithm for reclaiming storage space used by old versions of data objects that will no longer be accessed. We also propose an on-line backup algorithm that will permit the backup procedure to run in parallel with regular transactions. This integrated concurrency control and recovery scheme is being implemented in the LDM: the local database manager component of a distributed database management system, now being developed by Computer Corporation of America, that will support the ADAPLEX database application programming language [Chan81a, Smith81].

Index selection in a self-adaptive data base management system

We address the problem of automatically adjusting the physical organization of a data base to optimize its performance as its access requirements change. We describe the principles of the automatic index selection facility of a prototype self-adaptive data base management system that is currently under development. The importance of accurate usage model acquisition and data characteristics estimation is stressed. The statistics gathering mechanisms that are being incorporated into our prototype system are discussed. Exponential smoothing techniques are used for averaging statistics observed over different periods of time in order to predict future characteristics. An heuristic algorithm for selecting indices to match projected access requirements is presented. The cost model on which the decision procedure is based is flexible enough to incorporate the overhead costs of index creation, index storage and application program recompilation.

A recovery algorithm for a distributed database system

We describe a reliability algorithm being considered for DDM, a distributed database system under development at Computer Corporation of America. The algorithm is designed to tolerate clean site failures in which sites simply stop running. The algorithm allows the system to reconfigure itself to run correctly as sites fail and recover. The algorithm solves the subproblems of atomic commit and replicated data handling in an integrated manner.

Storage and access structures to support a semantic data model

ABSTRACT This paper describes the design of storage and access structures for a high performance Ada * compatible database management system. This system supports the database application programming language ADAPLEX [Smith81, Smitb82], which is the result of embedding the database sublanguage DAPLEX [Shipman81] in the general purpose language Ada [DoD80]. A prominent feature of the underlying data model is its support for generalization hierarchies [Smith77] which are intended to simplify the mapping from conceptual entities to database objects. An in-depth discussion of the rationale behind our choice of storage and access structures to support semantics intrinsic to the data model and to permit physical database organization tuning is provided in this paper.

An Ada-compatible distributed database management system

Adaplex is an integrated language for programming database applications. It results from the embedding of the database sublanguage Daplex in the general-purpose programming language Ada [1]. This paper describes the design of DDM, a general-purpose distributed database management system implemented in Ada that supports the use of Adaplex as interface language. There are two novel aspects in the design of this system. First, this is the first full-scale distributed database system to support a semantically rich, functional data model. DDM goes beyond systems like Distributed INGRES and R*(which are based on the relational technology) in providing advanced data modeling capabilities and ease of use. Second, this is the first full-function distributed DBMS designed to be compatible with the Ada programming environment. The coupling between Ada and Daplex has been achieved at the expression level which is much tighter than the statement level integration attained in previous systems. This tight coupling poses new implementation problems but also creates new opportunities for optimization. The current paper highlights the Adaplex language and discusses innovative aspects in DDMs design that are intended to meet the dual objectives of good performance and high data availability.

A tool kit for database programming in Ada

This paper describes an Ada-compatible database application development environment being designed and prototyped at Computer Corporation of America. This environment is intended to provide uniform access to centralized, homogeneously distributed, and heterogeneously distributed databases. There are two key interfaces: an interactive interface called Daplex which is based on a semantically rich data model and a powerful access language, and an application program interface called Adaplex which consists of an expression level integration of Daplex with Ada. The objective of this paper is to explain our rationale for designing Adaplex and to describe its support environment.