Managing Multiuser Databases - Database Processing: Fundamentals, Design, and Implementation - page 399

Before Action After

START

CUSTOMER
CNum OrderNum

CUSTOMER

Description AmtDue CNum OrderNum Description AmtDue

1. Add new-order data to
CUSTOMER. 123 1000 400 Baseballs $2400 123 1000 400 Baseballs $2400

250 Basketballs $6500

123 8000

SALESPERSON SALESPERSON

2. Add new-order data to
SALESPERSON.

Total-
Sales

Total-
Sales
JONES 9700

Name Commission Due Name Commission Due

$970

JONES $3200 $320

ORDER ORDER

3. Insert new ORDER.

OrderNum OrderNum

. . .
. . .
. . .
. . .
. . .
. . .
. . .

. . .
. . .
. . .
. . .
. . .
. . .
. . .
*FULL*

1000
2000
3000
4000
5000
6000
7000

1000
2000
3000
4000
5000
6000
7000

STOP

*FULL*

(a) Errors Introduced Without Transaction

Before Transaction After

Begin Transaction
Change CUSTOMER data
Change SALESPERSON data
Insert ORDER data
If no errors then
Commit Transactions
Else
Rollback Transaction
End If

CUSTOMER CUSTOMER

CNum OrderNum Description AmtDue CNumOrderNum Description AmtDue

400 Baseballs $2400 400 Baseballs $2400

123 1000 123 1000

SALESPERSON SALESPERSON

Total-
Sales

Total-
Sales
JONES 3200

Name Commission Due

$320

Name Commission Due

$320 JONES $3200

ORDER
OrderNum

ORDER
OrderNum

. . .
. . .
. . .
. . .
. . .
. . .
. . .
*FULL*

. . .
. . .
. . .
. . .
. . .
. . .
. . .
*FULL*

1000
2000
3000
4000
5000
6000
7000

1000
2000
3000
4000
5000
6000
7000

(b) Atomic Transaction Prevents Errors

Figure 9-3
transaction Processing
Example