The document discusses transaction logging and recovery. It explains that log records are written directly to stable storage and can indicate transaction start, read/write operations with old and new values, and transaction commit or abort. It provides an example of transactions T0 and T1 performing read and write operations, and shows how the log would appear at different times to allow for recovery in case of failures.

2.  Transaction Failure :
› Logical errors
› System errors
 System Crash
 Disk Failure

3.  Volatile Storage
 Non-Volatile Storage
 Stable Storage

4. X
Y
A
B
x1
y1
buffer
Buffer Block A
Buffer Block B
input(A)
output(B)
read(X)
write(Y)
disk
work area
of T1
work area
of T2
memory
x2

5.  Shadow Paging
 Log-based Recovery

7. Log records are written directly to stable storage.
Log Types:
 <Ti start>
 <Ti, X, V>
 <Ti, X, V1, V2>
 <Ti commit>
 <Ti abort>

8.  Transactions T0 and T1 (T0 executes before T1):
T0: read (A) T1 : read (C)
A: - A - 50 C:-C- 100
write (A) write (C)
read (B)
B:- B + 50
write (B)

11.  Below we show the log as it appears at three instances
of time.

12.  Transactions T0 and T1 (T0 executes before T1):
T0: read (A) T1 : read (C)
A: - A - 50 C:-C- 100
write (A) write (C)
read (B)
B:- B + 50
write (B)

15.  Below we show the log as it appears at three instances
of time.