tailieunhanh - Oracle® Database Concepts

The simplest way to think of Oracle’s implementation of read consistency is to imagine each user operating a private copy of the database, hence the multiversion consistency model. Read Consistency, Undo Records, and Transactions To manage the multiversion consistency model, Oracle must create a read-consistent set of data when a table is queried (read) and simultaneously updated (written). When an update occurs, the original data values changed by the update are recorded in the database undo records. As long as this update remains part of an uncommitted transaction, any user that later queries the modified data views the original. | ORACLE Oracle Database Concepts 10g Release 2 B14220-02 October 2005 Oracle Database Concepts 10g Release 2 B14220-02 Copyright 1993 2005 Oracle. All rights reserved. Primary Author Michele Cyran Contributing Author Paul Lane JP Polk Contributor Omar Alonso Penny Avril Hermann Baer Sandeepan Banerjee Mark Bauer Bill Bridge Sandra Cheevers Carol Colrain Vira Goorah Mike Hartstein John Haydu Wei Hu Ramkumar Krishnan Vasudha Krishnaswamy Bill Lee Bryn Llewellyn Rich Long Diana Lorentz Paul Manning Valarie Moore Mughees Minhas Gopal Mulagund Muthu Olagappan Jennifer Polk Kathy Rich John Russell Viv Schupmann Bob Thome Randy Urbano Michael Verheij Ron Weiss Steve Wertheimer The Programs which include both the software and documentation contain proprietary information they are provided under a license agreement containing restrictions on use and disclosure and are also protected by copyright patent and other intellectual and industrial property laws. Reverse engineering disassembly or decompilation of the Programs except to the extent required to obtain interoperability with other independently created software or as specified by law is prohibited. The information contained in this document is subject to change without notice. If you find any problems in the documentation please report them to us in writing. This document is not warranted to be error-free. Except as may be expressly permitted in your license agreement for these Programs no part of these Programs may be reproduced or transmitted in any form or by any means electronic or mechanical for any purpose. If the Programs are delivered to the United States Government or anyone licensing or using the Programs on behalf of the United States Government the following notice is applicable . GOVERNMENT RIGHTS Programs software databases and related documentation and technical data delivered to . Government customers are commercial computer software or commercial technical data pursuant to the applicable