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T1
T2
BEGIN
READ (A)
A :
=
A
+
100
WRITE (A)
BEGIN
READ (A)
A :
=
A
-
50
WRITE (A)
READ (B)
B :
=
B
+
200
WRITE (B)
COMMIT
END
READ (B)
B :
100
WRITE (B)
COMMIT
END
SCHEDULE-1
NON-SERIAL SCHEDULE
Figure 15-14
B
=
-
Example of a nonserial schedule.
T1
T2
BEGIN
READ (A)
A :
=
A
+
100
WRITE (A)
BEGIN
READ (A)
A :
=
A
-
50
WRITE (A) of T2 does
not conflict with
READ (B) of T1.
Therefore, these two
operations are
swapped.
READ (B)
B :
=
B
+
200
WRITE (A)
WRITE (B)
COMMIT
READ (B)
END
B :
=
B
-
100
WRITE (B)
COMMIT
END
SCHEDULE-2
OBTAINED BY
TRANSACTION SWAPPING
Figure 15-15
Schedule obtained by operation swapping.
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