Using the following execution shown below, explain what is done in each of the A
ID: 3869248 • Letter: U
Question
Using the following execution shown below, explain what is done in each of the ARIES recovery algorithm phases:
LSN
LOG
00
begin_checkpoint
10
end_checkpoint
20
update: T1 writes P1
30
update: T2 writes P2
40
update: T3 writes P3
50
T2 commit
60
update: T3 writes P2
70
T2 end
80
update: T1 writes P5
90
T3 abort
CRASH, RESTART
LSN
LOG
00
begin_checkpoint
10
end_checkpoint
20
update: T1 writes P1
30
update: T2 writes P2
40
update: T3 writes P3
50
T2 commit
60
update: T3 writes P2
70
T2 end
80
update: T1 writes P5
90
T3 abort
CRASH, RESTART
Explanation / Answer
00 begin_checkpoint : Indicates when check point began
10 end_checkpoint : Contains current Xact table and dirty page table.
20 update: T1 writes P1: Add (T1,20) to TT and (P1,20) to DPT
30 update: T2 writes P2: Add (T2,30) to TT and (P2,30) to DPT.
40 update: T3 writes P3: Add (T3,40) to TT and (P3,40) to DPT
50 T2 commit: Change status of T2 to C
60 update: T3 writes P2: Change (T3,40) to (T3,60)
70 T2 end: Remove T2 from TT
80 update: T1 writes P5: Change (T1,20) to (T1,70) and add (P5,70) to DPT
90 T3 abort: No action
CRASH, RESTART
Undo Phase:
At the end of analysis,
the transaction table contains the following entries:
(T1,80), and (T3,60).
The Dirty Page Table has the following entries:
(P1,20), (P2,30), (P3,40), and (P5,80).
Starts from the end to the begin of the oldest non-committed transaction.
80 Undo the changes in P5 by T1.
60 Undo the changes on P2 by T3.
40 Undo the changes on P3 by T3.
20 Undo the changes on P1 by T1.
Redo Phase
20 No action on P1. T1 is a lost transaction.
30 Redo the change in P2 by T2.
40 No action on P3. T3 is a lost transaction.
60 No action on P2. T3 is a lost transaction.
80 No action on P5. T1 is a lost transaction.
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