The database contains the following data items and their values:A = 1000B = 1500C = 3000Log file is empty at first (contains no entries). x, y, z, t - transaction local variables (not stored in DB).The following transaction execution schedule is given:T0T1T2START TRANSACTIONWRITE(2000, B) Start TRANSACTIONREAD (x, A)x=x+n1n2n3n4n5WRITE (x, A) CHECKPOINT START TRANSACTIONCOMMIT TRANSACTION READ (y, B)y = y-n3n4n5 READ (z, C)z=z+n1n2n3n4WRITE (z, C) WRITE (y, B) CHECKPOINT COMMIT TRANSACTION Read (t, C) SYSTEM FAILThe activity logging is performed (in the database). Log file entries are not buffered and are saved to disk when each new log file entry is inserted (Immediate Database Modification scheme is used). No fuzzy checkpointing is used. Any of Early lock release and Logical Undo Loging are not used.a) What will be the contents of the log file when the System fail occurs?b) Which transaction system will roll forward during recovery and which roll back?c) What will be the full contents of the log file after system restore / recovery?

Database Recovery A major responsibility of the database administrator is to prepare for the…

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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

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The database contains the following data items and their values:

A = 1000
B = 1500
C = 3000

Log file is empty at first (contains no entries). x, y, z, t - transaction local variables (not stored in DB).

The following transaction execution schedule is given:

T0	T1	T2
START TRANSACTION WRITE(2000, B)
	Start TRANSACTION READ (x, A) x=x+n₁n₂n₃n₄n₅ WRITE (x, A)
CHECKPOINT
		START TRANSACTION
COMMIT TRANSACTION
	READ (y, B) y = y-n₃n₄n₅
		READ (z, C) z=z+n₁n₂n₃n₄ WRITE (z, C)
	WRITE (y, B)
CHECKPOINT
		COMMIT TRANSACTION
	Read (t, C)
SYSTEM FAIL

The activity logging is performed (in the database). Log file entries are not buffered and are saved to disk when each new log file entry is inserted (Immediate Database Modification scheme is used). No fuzzy checkpointing is used. Any of Early lock release and Logical Undo Loging are not used.

a) What will be the contents of the log file when the System fail occurs?

b) Which transaction system will roll forward during recovery and which roll back?

c) What will be the full contents of the log file after system restore / recovery?

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