please explain throughly...i need to understand this example for my final exam S
ID: 3646429 • Letter: P
Question
please explain throughly...i need to understand this example for my final examShow intermediate steps leading to your answers for the following problem.(thank you in advance)
(1) The following shows a schedule for two transactions T1 and T2.
T1 T2
read(B)
read(B)
write(B)
write(A)
read(A)
write(A)
Use the timestamp protocol approach to show how the following sequence of operations is executed.
read(B) in T2, read(B) in T1, write(B) in T2, read(A) in T2, write(A) in T1, write(A) in T2.
We assume the following initial values. show how values are used for equation please
TS(T1) = 5,
TS(T2) = 7,
R-timestamp(A) = 0,
W-timestamp(A) = 0,
R-timestamp(B) = 0,
W-timestamp(B) = 0
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example
If TS(Ti) < W-Timestamp(Q), Then This Implies That Ti Needs To Read A Value Of Q Already Written
The "read" Operation Is Rejected And Ti Is Rolled Back
If TS(Ti) ? W-Timestamp(Q), Then The "read" Operation Is Executed And R-Timestamp(Q) Is Set To Max (R-Timestamp(Q), TS(Ti))
If TS(Ti) < W-Timestamp(Q), Then This Implies That Ti Needs To Read A Value Of Q Already Written
The "read" Operation Is Rejected And Ti Is Rolled Back
If TS(Ti) ? W-Timestamp(Q), Then The "read" Operation Is Executed And R-Timestamp(Q) Is Set To Max (R-Timestamp(Q), TS(Ti))
Explanation / Answer
W-timestamp(Y) is the largest time-stamp of any transaction that executed write(Y) successfully.
R-timestamp(Y) is the largest time-stamp of any transaction that executed read(Y) successfully.
A transaction performs read operation if its R-timestamp(y)<=TS(T).
A transaction performs write operation if its If W-timestamp(y)<=TS(T) and if R-timestamp(X) >TS(T) then the transaction aborts and rolls back.
According to the TimeStamp protocol, as the process T1 has lesser TS than T2, it starts its schedule first.
hence the sequence is as follows,
In T1: In T2:
1.read(A)
2.write(A)
3.read(B)
4.write(B)
5.read(B)
6.write(A)
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