Suppose we (incorrectly) modify the recovery algorithm of Section 19.4 tonote log actions taken during transaction rollback. When recovering from asystem crash, transactions that were rolled back earlier would then be includedin undo-list and rolled back again. Give an example to show how actions takenduring the undo phase of recovery could result in an incorrect database state.(Hint: Consider a data item updated by an aborted transaction and then updatedby a transaction that commits.)
Suppose we (incorrectly) modify the recovery algorithm of Section 19.4 tonote log actions taken during transaction rollback. When recovering from asystem crash, transactions that were rolled back earlier would then be includedin undo-list and rolled back again. Give an example to show how actions takenduring the undo phase of recovery could result in an incorrect database state.(Hint: Consider a data item updated by an aborted transaction and then updatedby a transaction that commits.)
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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| Suppose we (incorrectly) modify the recovery note log actions taken during transaction rollback. When recovering from a system crash, transactions that were rolled back earlier would then be included in undo-list and rolled back again. Give an example to show how actions taken during the undo phase of recovery could result in an incorrect (Hint: Consider a data item updated by an aborted transaction and then updated by a transaction that commits.) |
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