This practice problem assists you in understanding commitment control and its requirements. These steps assume that you are familiar with the i5/OS™ licensed program, the data file utility (DFU), and this topic collection.
The logic flow might help you further understand this practice program for commitment control.
To use commitment control, follow these steps:
10 A R ITMR 20 A ITEM 2 30 A ONHAND 5 0 40 A K ITEM
10 A R TRNR 20 A QTY 5 0 30 A ITEM 2 40 A USER 10
10 LIFO 20 A R TRNR PFILE (TRNP) 30 A K USER
| Item | On hand |
|---|---|
| AA | 450 |
| BB | 375 |
| CC | 4000 |
PGM DCL &USER *CHAR LEN(10) RTVJOBA USER(&USER) CALL ITMPCS PARM(&USER) ENDPGM
This is the control program that calls the ITMPCS program. It retrieves the user name and passes it to the processing program. This application assumes that unique user names are used.
There are two formats, the first for the basic prompt display and the second to allow the operator to review the last transaction entered. This display file is used by the ITMPCS program.
SEQNBR *... ... 1 ... ... 2 ... ... 3 ... ... 4 ... ... 5 ... ... 6 ... ... 7 ..
1.00 A R PROMPT
2.00 A CA03(93 'End of program')
3.00 A CA04(94 'Review last')
4.00 A SETOFF(64 'No rcd to rvw')
5.00 A 1 2'INVENTORY TRANSACTIONS'
6.00 A 3 2'Quantity'
7.00 A QTY 5 0I +1
8.00 A 61 ERRMSG('Invalid +
9.00 A quantity' 61)
10.00 A +5'ITEM'
11.00 A ITEM 2 I +1
12.00 A 62 ERRMSG('Invalid +
13.00 A Item number' 62)
14.00 A 63 ERRMSG('Rollback +
15.00 A occurred' 63)
16.00 A 64 24 2'CF4 was pressed and +
17.00 A there are no +
18.00 A transactions for +
19.00 A this user'
20.00 A DSPATR(HI)
21.00 A 23 2'CF4 Review last +
22.00 A transaction'
23.00 A R REVW
24.00 A 1 2'INVENTORY TRANSACTIONS'
25.00 A +5'REVIEW LAST TRANSACTION'
26.00 A 3 2'Quantity'
27.00 A QTY 5 0 +1EDTCDE(Z)
28.00 A +5'Item'
29.00 A ITEM 2 +1
SEQNBR *... ... 1 ... ... 2 ... ... 3 ... ... 4 ... ... 5 ... ... 6 ... ... 7 .. 1.00 FITMP UF E K DISK 2.00 F* KCOMIT 3.00 FTRNP O E DISK 4.00 F* KCOMIT 5.00 FTRNL IF E K DISK 6.00 F TRNR KRENAMETRNR1 7.00 FITMPCSD CF E WORKSTN 8.00 C* Enter parameter with User name for -TRNP- file 9.00 C *ENTRY PLIST 10.00 C PARM USER 10 11.00 C LOOP TAG 12.00 C EXFMTPROMPT 13.00 C* Check for CF3 for end of program 14.00 C 93 DO End of Pgm 15.00 C SETON LR 16.00 C RETRN 17.00 C END 18.00 C* Check for CF4 for review last transaction 19.00 C 94 DO Review last 20.00 C* Check for existence of a record for this user in -TRNL- file 21.00 C USER CHAINTRNR1 64 Not found 22.00 C 64 GOTO LOOP 23.00 C EXFMTREVW 24.00 C GOTO LOOP 25.00 C END 26.00 C* Access Item record 27.00 C ITEM CHAINITMR 62 Not found 28.00 C* Handle -not found- Condition 29.00 C 62 GOTO LOOP 30.00 C* Does sufficient quantity exist 31.00 C ONHAND SUB QTY TEST 50 61 Minus 32.00 C* Handle insufficient quantity 33.00 C 61 DO 34.00 C* Release Item record which was locked by the CHAIN for update 35.00 C EXCPTRLSITM 36.00 C GOTO LOOP 37.00 C END 38.00 C* Change ONHAND and update the Item record 39.00 C Z-ADDTEST ONHAND 40.00 C UPDATITMR 41.00 C* Test for Special Simulation Conditions 42.00 C ITEM IFEQ 'CC' 43.00 C* Simulate program need for rollback 44.00 C QTY IFEQ 100 45.00 C SETON 63 Simult Rlbck 46.00 C* ROLBK 47.00 C GOTO LOOP 48.00 C END 49.00 C* Simulate an abnormal program cancellation by Div by zero 50.00 C* Operator Should respond -C- to inquiry message 51.00 C QTY IFEQ 101 52.00 C Z-ADD0 ZERO 30 53.00 C TESTZ DIV ZERO TESTZ 30 Msg occurs 54.00 C END 55.00 C* Simulate an abnormal job cancellation by DSPLY. 56.00 C* Operator Should System Request to another job 57.00 C* and cancel this one with OPTION(*IMMED) 58.00 C QTY IFEQ 102 59.00 C 'CC=102' DSPLY Msg occurs 60.00 C END 61 00 C END ITEM=CC 62.00 C* Write the -TRNP- file 63 00 C WRITETRNR 64.00 C* Commit the update to -ITMP- and write to -TRNP- 65.00 C* COMIT 66.00 C GOTO LOOP 67.00 OITMR E RLSITM
| Quantity | Item |
|---|---|
| 3 | AA |
| 4 | BB |
| Quantity | Item |
|---|---|
| 5 | FF (Invalid item number message occurs.) |
| 9000 | BB (Insufficient quantity error message occurs.) |
| 100 | CC (Rollback message occurs.) |
| 102 | CC (RPG DSPLY operation must occur. Press the Enter key.) |
| 101 | CC (The program must display an inquiry message stating that a divide by zero condition has occurred or end, depending on the setting of job attribute INQMSGRPY. If the inquiry message appears, enter C to cancel the RPG program and then C to cancel the CL program on the subsequent inquiry. This simulates an unexpected error condition.) |
See if the records AA and BB have been updated correctly. The values must be AA = 447, BB = 371, and CC = 3697. Note that the quantities subtracted from CC occurred, but the transaction records were not written.
The IMAGES parameter uses a default of *AFTER, meaning that only after-image changes of the records appear in the journal. The files ITMP and TRNP have now started journaling.
Normally, you save the files after starting journaling. You cannot apply journaled changes to a restored file that does not have the same JID as the journal entries. Because this practice problem does not require you to apply journaled changes, you can skip saving the journaled files.
| Quantity | Item |
|---|---|
| 5 | AA |
| 6 | BB |
End the program by pressing F3.
Note the entries appearing in the journal. The same sequence of entries (R UP = update of ITMP followed by R PT = record added to TRNP) occurs in the journal as was performed by the program. This is because a logical file is defined over the physical file TRNP and the system overrides the RPG default. If no logical file existed, the RPG assumption of SEQONLY(*YES) is used, and a block of PT entries appear because the records are kept in the RPG buffer until the block is full.
PGM
DCL &USER *CHAR LEN(10)
RTVJOBA USER(&USER)
* STRCMTCTL LCKLVL(*CHG)
CALL ITMPCS PARM(&USER)
* MONMSG MSGID(RPG9001) EXEC(ROLLBACK)
* ENDCMTCTL
ENDPGM
The STRCMTCTL command sets up the commitment control environment. The LCKLVL word specifies that records read for update but not updated can be released during the transaction. The MONMSG command handles any RPG escape messages and performs a ROLLBACK in case the RPG program abnormally ends. The ENDCMTCTL command ends the commitment control environment.
| Quantity | Item |
|---|---|
| 7 | AA |
| 8 | BB |
Note the values on the display. There must be two commits because two commit statements were run in the program.
| Entry | Meaning |
|---|---|
| C BC | STRCMTCTL command occurred. |
| C SC | Start commit cycle. This occurs whenever the first database operation in the transaction causes a record to be inserted, updated, or deleted as part of commitment control. |
| C CM | Commit operation has occurred. |
| C EC | ENDCMTCTL command occurred. |
The commitment control before-images and after-images (R UB and R UP types) automatically occur even though you had originally requested IMAGES(*AFTER) for the journal.
| Quantity | Item |
|---|---|
| 12 | AA |
| 100 | CC (This is the condition to simulate the need for an application use of rollback. The CC record in the ITMP file, which was updated by RPG statement 40.00 is rolled back.) |
The last committed transaction is the entry for item AA.
Note the values on the display and how they have been changed by the rollback.
Note the additional entries that appear in the journal for the use of the rollback entry (C RB entry). When the ITMP record is rolled back, three entries are placed in the journal. This is because any change to the database file under commitment control produces a before (R BR) and after (R UR) entry.
The last entry is the RB entry for the end of the rollback.
| Quantity | Item |
|---|---|
| 13 | AA |
| 101 | CC (This is the condition to simulate an unexpected error condition, which causes the program to end. The simulation occurs by dividing a field by 0. The program will display an inquiry message or end, depending on the setting of the job attribute INQMSGRPY. If the inquiry message appears, enter C to end the program. Because the CL program was changed to monitor for RPG program errors, the second inquiry which occurred does not occur.) |
The same type of rollback handling has occurred, but this time the rollback was caused by the EXEC parameter of the MONMSG command in the CL program instead of the RPG program. Display the two RB entries to see which program caused them.
| Quantity | Item |
|---|---|
| 14 | AA |
| 102 | CC (The RPG DSPLY operation must occur to the external message queue. Use the System Request key and select option 1 on the system request menu to transfer to a secondary job.) |
Note the last committed transaction. It must be the AA item entered earlier.
The same type of rollback handling has occurred, but this time the rollback was caused by the system instead of one of the programs. The RB entry was written by the program QWTPITPP, which is the work management abnormal end program.
You have now used the basic functions of commitment control. You can proceed with commitment control on your applications or try some of the other functions such as: