Universität Karlsruhe (TH) © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Chapter 3 Isolation: Examples.

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Presentation transcript:

Universität Karlsruhe (TH) © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Chapter 3 Isolation: Examples

2 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Example 1

3 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Miniworld Sales database of a wine dealer:

4 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Sales transaction 1. Sales transaction (R: Riesling) Ignored in the R/W model: Local action Transaction in the R/W model: t = r(R) w(R) 2. Two sales persons: Miller and Smith. 3. Database: page  tuple.

5 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update Mr. Miller‘s update has been lost (lost update). Schema: r 1 (R) r 2 (R) w 1 (R) w 2 (R)

6 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (1) Cancelation ignored. Never became valid! Schema: r 1 (R) w 1 (R) r 2 (R) a 1 w 2 (R)

7 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (2) Dirty read: Read a value after it was changed by a second transaction but before its validity could be guaranteed. Occurs whenever a transaction reads a value changed by a second transaction before that one committed.

8 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Compute the sum total of wines on stock. Inconsistent Read (1) Correct a mixup in sales registration.

9 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (2) persistent transient 

10 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 inconsistent read: Read of states that are valid at different times  inconsistent view of the database. In the example: resulting count incorrect (missed 10 bottles). Schema: r 1 (G) r 1 (R) r 2 (M) r 1 (S) w 2 (M) r 2 (G) r 1 (W) w 2 (G) c 2 r 1 (M) c 1 Inconsistent Read (3)

11 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Threats to the global consistency Interaction of reads and writes :  Two concurrent read-only transactions have no mutual impact, since in the read/write model the only interactions possible between transactions are via database writes.  If a read transaction competes with a write transaction, the write transaction remains unaffected and hence the database consistent. On the other hand, the write transaction may have an effect on the read transaction.  Two concurrent write transactions may affect each other, and the database may become inconsistent.

12 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Example 2

13 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Scenario Relations:  TICKET (ticketNo, name)T  BOOKING (flightNo, ticketNo, seatCode, date)B Transactions:  t 1 : Check the consistency of passenger list und bookings,  t 2 : Rebook a passenger group,  t 3 : Cancel a booking. Simplification:  Relations fit on a single page.

14 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Transaction t 1 Print number of tickets sold for 12 August 2000 plus the list of the associated passengers : selectcount (distinct ticketNo) fromBOOKING wheredate = 12-AUG-00; print number of tickets; selectname fromTICKET whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00); print passenger list; commit; read BOOKING read TICKET BOOKING already read r/w model for t 1 : r 1 (B) r 1 (T) c 1.

15 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Transaction t 2 Rebook passengers in row 19 from LH500 on 12 August 2000 to 11 August 2000 and mark ticket number: updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E" or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E" or seatCode = "19G"); commit; read BOOKING read TICKET BOOKING already read r/w model for t 2 : r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2. write TICKET write BOOKING Note that the first write depends on the two reads.

16 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Transaction t 3 Cancel the ticket with number : delete from TICKET where ticketNo = ; delete from BOOKING where ticketNo = ; commit; r/w model for t 3 : r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3. read BOOKING read TICKET write TICKET write BOOKING

17 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (1) selectcount (distinct ticketNo) fromBOOKING wheredate = 12-AUG-00; Print number of tickets; selectname fromTICKET whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00); print passenger list; commit; updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flugNr = "LH500" and(seatCode = "19D" or seatCode = "19E" or seatCode = "19G"); commit; read-write interaction by interrupting the reader S1: r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 r 1 (B) r 2 (B) r 1 (T) r 2 (T) w 2 (T) w 2 (B)

18 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (2) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00

19 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (3) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 Output t 1 : number of tickets = 3.

20 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (4) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads BOOKING and selects.

21 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (5) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads TICKET and selects.

22 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (6) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 updates and writes TICKET.

23 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (7) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 updates and writes BOOKING.

24 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent Read (8) r 1 (B) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 1 (T) c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 Output t 1 : empty passenger list.

25 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 No problem updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G"); commit; S2: r 2 (B) r 2 (T) r 1 (B) r 1 (T) c 1 w 2 (T) w 2 (B) c 2 selectcount (distinct ticketNo) fromBOOKING wheredate = 12-AUG-00; print number of tickets; selectname fromTICKET whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00); print passenger list; commit; read-write interaction by interrupting the writer No problem, because t 1 reads a database state that was not yet changed. Tough luck for t 1 that it is no longer valid shortly afterwards. r 1 (B) r 2 (B) r 1 (T) r 2 (T) w 2 (T) w 2 (B)

26 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (1) updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G"); commit; selectcount (distinct ticketNo) fromBOOKING wheredate = 12-AUG-00; print number of tickets; selectname fromTICKET whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00); print passenger list; commit; r 1 (B) r 2 (B) r 1 (T) r 2 (T) w 2 (T) w 2 (B) Effect on t 1 as in S1. S3: r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) c 1 w 2 (B) c 2 read-write interaction by interrupting the writer

27 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (2) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00

28 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (3) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads BOOKING and selects.

29 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (4) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads TICKET and selects.

30 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (5) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 updates and writes TICKET.

31 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (6) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 Output t 1 : number of tickets = 3.

32 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (7) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 Output t 1 : empty passenger list.

33 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (8) r 2 (B) r 2 (T) w 2 (T) r 1 (B) r 1 (T) w 2 (B) c 2 c 1 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 updates and writes BOOKING.

34 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Dirty Read (9) „dirty read“ leaves open whether the transient state is consistent or not. Take schedule S4: r 2 (B) r 2 (T) w 2 (T) w 2 (B) r 1 (B) r 1 (T) c 2 c 1. r 1 (B) r 1 (T) has a consistent output despite dirty read. Still dangerous! Take abort of T 2 : S4: r 2 (B) r 2 (T) w 2 (T) w 2 (B) r 1 (B) r 1 (T) a 2 c 1. Because t 2 leaves no trace t 1 reads a state that never existed!

35 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (1) writer-writer interaction by interrupting one of the writers S5: r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 delete from TICKET where ticketNo = ; delete from BOOKING where ticketNo = ; commit; updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G"); commit; r 2 (B) r 2 (T) w 2 (T) w 2 (B) r 3 (T) w 3 (T) r 3 (B) w 3 (B)

36 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (2) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00

37 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (3) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 reads TICKET and selects.

38 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (4) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 writes TICKET.

39 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (5) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads BOOKING and selects.

40 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (6) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads TICKET and selects.

41 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (7) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 writes TICKET.

42 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (8) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 writes BOOKING.

43 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (9) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 reads BOOKING.

44 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Inconsistent + Dirty Read (10) r 3 (T) w 3 (T) r 2 (B) r 2 (T) w 2 (T) w 2 (B) c 2 r 3 (B) w 3 (B) c 3 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 writes BOOKING.

45 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (1) updateTICKET setticketNo = ticketNo whereticketNo in (selectticketNo fromBOOKING wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G" )); updateBOOKING setdate = 11-AUG-00, ticketNo = ticketNo wheredate = 12-AUG-00 and flightNo = "LH500" and(seatCode = "19D" or seatCode = "19E„ or seatCode = "19G"); commit; delete from TICKET where ticketNo = ; delete from BOOKING where ticketNo = ; commit; writer-writer interaction by interrupting one of the writers r 2 (B) r2(T)r2(T) w2(T)w2(T) w2(B)w2(B) r3(T)r3(T) w3(T)w3(T) r 3 (B) w 3 (B) S6: r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2

46 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (2) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00

47 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (3) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads BOOKING and selects.

48 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (4) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 reads TICKET and selects.

49 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (5) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 reads TICKET and selects.

50 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (6) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 writes TICKET.

51 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (7) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 12-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 reads BOOKING and selects.

52 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (8) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG-00 LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 3 writes BOOKING.

53 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (9) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH G 12-AUG-00 LH E 12-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 writes TICKET.

54 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (10) r 2 (B) r 2 (T) r 3 (T) w 3 (T) r 3 (B) w 3 (B) c 3 w 2 (T) w 2 (B) c 2 flightNo ticketNo seatCode date ticketNo name LH B 26-AUG Kuhn_Mrs_E LH A 29-SEP Pulkowski_Mr_S LH F 03-OCT Witte_Mr_R LH D 04-SEP Krakowski_Mrs_P LH D 08-SEP Posselt_Mr_D LH C 09-SEP Gimbel_Mr_M LH E 01-SEP Muelle_Mrs_J LH K 07-AUG Bender_Mr_P LH A 11-AUG Lockemann_Mr_P LH K 11-AUG Simpson_Mr_B LH D 01-AUG Weinand_Mr_C LH E 14-AUG-00 LH K 03-SEP-00 LH D 10-SEP-00 LH G 21-JUL-00 LH D 05-AUG-00 LH D 11-AUG-00 LH G 11-AUG-00 LH E 11-AUG-00 LH K 05-AUG-00 LH A 06-AUG-00 t 2 writes BOOKING.

55 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Lost Update (11) Note: Neither t 2 nor t 3 include „inconsistent read“ or „dirty read“. „lost update“ is an independent phenomenon!

56 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 Example 3

57 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 OLTP Example: Debit/Credit void main ( ) { EXEC SQL BEGIN DECLARE SECTION int b /*balance*/, a /*accountid*/, amount; EXEC SQL END DECLARE SECTION; /* read user input */ scanf (“%d %d”, &a, &amount); /* read account balance */ EXEC SQL Select Balance into :b From Account Where Account_Id = :a; /* add amount (positive for debit, negative for credit) */ b = b + amount; /* write account balance back into database */ EXEC SQL Update Account Set Balance = :b Where Account_Id = :a; EXEC SQL Commit Work; } © Weikum, Vossen, 2002

58 © 2006 Univ,Karlsruhe, IPD, Prof. Lockemann/Prof. BöhmTAV 3 OLTP Example: Concurrent Executions P1TimeP2 Select Balance Into :b 1 From Account 1 Where Account_Id = :a /* b 1 =0, a.Balance=100, b 2 =0 */ Select Balance Into :b 2 2From Account Where Account_Id = :a /* b 1 =100, a.Balance=100, b 2 =100 */ b1 = b /* b 1 =50, a.Balance=100, b 2 =100 */ 4b 2 = b /* b 1 =50, a.Balance=100, b 2 =200 */ Update Account Set Balance = :b 1 5 Where Account_Id = :a /* b 1 =50, a.Balance=50, b 2 =200 */ Update Account 6Set Balance = :b 2 Where Account_Id = :a /* b 1 =50, a.Balance=200, b 2 =200 */ © Weikum, Vossen, 2002

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