a. Is the old-value part of an update log record required any more? Why or why not? b. If old values are not stored in update log records, transaction undo. Is clearly not feasible. How would the redo-phase of recovery have to be modified as a result? C. Deferred modification can be implemented by keeping updated data items in local memory of transactions, and reading data items that have not been updated directly from the database buffer. Suggest how to efficiently implement a data item read, ensuring that a trans action sees its own updates.

a. Is the old-value part of an update log record required any more? Why or why not? b. If old values are not stored in update log records, transaction undo. Is clearly not feasible. How would the redo-phase of recovery have to be modified as a result? C. Deferred modification can be implemented by keeping updated data items in local memory of transactions, and reading data items that have not been updated directly from the database buffer. Suggest how to efficiently implement a data item read, ensuring that a trans action sees its own updates.

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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