TIME-CONSTRAINED TRANSACTION MANAGEMENT. Real-Time Constraints in Database Transaction Systems

Transcription

1 TIME-CONSTRAINED TRANSACTION MANAGEMENT Real-Time Constraints in Database Transaction Systems

2 The Kluwer International Series on ADV ANCES IN DATABASE SYSTEMS Other books in the Series: Series Editor Ahmed K. Elmagarmid Purdue University West Lafayette, IN DATABASE CONCURRENCY CONTROL: Methods, Performance, and Analysis by Alexander Thomasian, IBM T. J. Watson Research Center TIME-CONSTRAINED TRANSACTION MANAGEMENT Real-Time Constraints in Database Transaction Systems by Nandit R. Soparkar, Henry F. Korth, Abraham Silberschatz SEARCHING MULTIMEDIA DATABASES BY CONTENT by Christos F aloutsos REPLICATION TECHNIQUES IN DISTRIBUTED SYSTEMS by Abdelsalam A. Helal, Abdelsalam A. Heddaya, Bharat B. Bhargava The Kluwer International Series on Advances in Database Systems addresses the following goals: To publish thorough and cohesive overviews of advanced topics in database systems. To publish works which are larger in scope than survey articles, and which will contain more detailed background information. To provide a single point coverage of advanced and timely topics. To provide a forum for a topic of study by many researchers that may not yet have reached a stage of maturity to warrant a comprehensive textbook.

3 TI M E-CONSTRAI N ED TRANSACTION MANAGEMENT Real-Time Constraints in Database Transaction Systems Nandit R. SOPARKAR The University of Michigan Ann Arbor, Michigan, USA Henry F. KORTH Bell Laboratories, Lucent Technologies Inc. Murray Hill, New Jersey, USA Abraham SILBERSCHATZ Bell Laboratories, Lucent Technologies Inc. Murray Hill, New Jersey, USA KLUWER ACADEMIC PUBLISHERS Boston/London/Dordrecht

4 Distributors for North America: Kluwer Academic Publishers 101 Philip Drive Assinippi Park Norwell, Massachusetts USA Distributors for all other countries: Kluwer Academic Publishers Group Distribution Centre Post Office Box AH Dordrecht, THE NETHERLANDS Library of Congress Cataloging-in-Publication Data A C.I.P. Catalogue record for this book is available from the Library of Congress. The publisher offers discounts on this book when ordered in bulk quantities; For more information contact: Sales Department, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, MA lsbn-13: DOl: / e-lsbn-13: Copyright 1996 by Kluwer Academic Publishers Softcover reprint of the hardcover 1 st edition 1996 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, Massachusetts Printed on acid-free paper.

5 CONTENTS LIST OF FIGURES PREFACE Vll ix 1 INTRODUCTION Traditional Transactions Temporal Considerations Related Work Overview 19 2 A MODEL Centralized Environments Distributed Executions 40 3 CENTRALIZED SCHEDULING Performance Metrics Traditional Scheduling Optimization in Scheduling Countering Intractability Uncertainty in Scheduling 74 4 DISTRIBUTED SCHEDULING Integrating Local Executions A Synchronization Protocol Restrictions on Executions Other Integration Issues Global Atomic Commitment 91

6 VI TIME-CONSTRAINED TRANSACTION MANAGEMENT 5 SEMANTICS IN SCHEDULING Adaptive Commitment Data-value Partitioning CONCLUSIONS Issues in I/O Scheduling Online Wider Applicability In Summary 132 REFERENCES 135 INDEX 143

7 LIST OF FIGURES Chapter Concurrency control of transactions 1.2 Impossible global SG using 2PL and 2PC Chapter Temporal annotations for a schedule 2.2 Example of incorrect synchronization 2.3 Distributed TCTM system structure Chapter Abstract back-end architectures Chapter Overlapped synchronization intervals 4.2 Impossible cycle with synchronization protocol Chapter Using compensation in adaptive commitment Chapter Pipelined batched-online scheduling and execution

8 PREFACE Transaction processing is an established technique for the concurrent and faulttolerant access of persistent data. While this technique has been successful in standard database systems, factors such as time-critical applications, emerging technologies, and a re-examination of existing systems suggest that the performance, functionality and applicability of transactions may be substantially enhanced if temporal considerations are taken into account. That is, transactions should not only execute in a "legal" (i.e., logically correct) manner, but they should meet certain constraints with regard to their invocation and completion times. Typically, these logical and temporal constraints are application-dependent, and we address some fundamental issues for the management of transactions in the presence of such constraints. Our model for transaction-processing is based on extensions to established models, and we briefly outline how logical and temporal constraints may be expressed in it. For scheduling the transactions, we describe how legal schedules differ from one another in terms of meeting the temporal constraints. Existing scheduling mechanisms do not differentiate among legal schedules, and are thereby inadequate with regard to meeting temporal constraints. This provides the basis for seeking scheduling strategies that attempt to meet the temporal constraints while continuing to produce legal schedules. For centralized scheduling of transactions, we discuss the feasibility of achieving optimal results in terms of meeting the logical and temporal constraints. In most cases, this is shown to be intractable using results from existing studies in scheduling. Thereafter, we describe the means to achieve good results based on existing heuristics. Also, since the execution time estimates that are used in such studies are prone to be undependable, the issue of dealing with timing uncertainties in the context of scheduling is addressed. Time-constrained transactions find use in the development of several inherently distributed applications. The characteristic feature of such situations is the distributed loci of scheduling control. For reasons of efficiency and fault-tolerance, each local scheduler is necessarily autonomous in that its operation is oblivious

9 x TIME-CONSTRAINED TRANSACTION MANAGEMENT of the other schedulers. We provide effective means for achieving legal distributed schedules by the synchronization of logically correct local schedules. Additionally, we study the issue of meeting temporal constraints for transactions executing in such distributed environments. In doing so, ensuring the atomicity of distributed transactions in a failure-prone environment appears to be problematic since it is impossible to achieve with bounded execution times. Thereafter, we discuss exploiting application-specific semantics to alleviate this problem, where the key idea is to utilize decentralized transaction commitment strategies to ensure less stringent requirements on atomicity. The scope of our discussions is broad since meeting both logical and temporal constraints involves many considerations. We discuss issues regarding timing estimates, the software and hardware architectures, and the target applications; in detail, for some instances. While our research is based on a specific model, the results may be generalized to others. Therefore, the issues raised, and the techniques developed, represent several fundamental considerations in the management of time-constrained transactions. Finally, our research provides the basis for new directions in research in diverse related areas such as database technology, distributed systems, real-time systems, fault-tolerant systems, and scheduling theory. We would like to acknowledge several individuals with whom we have had useful discussions in the context of our research. They include Don Batory, Hector Garcia-Molina, Don Fussell, H.V. Jagadish, Eliezer Levy, Al Mok, Carlo Zaniolo, and several others. Also, we would like to thank Ahmed Elmagarmid and Scott Delman for assistance with reviewing and producing this monograph. Ann Arbor, Michigan Murray Hill, New Jersey Murray Hill, New Jersey N.R.S. H.F.K. A.S.