How many conflicts are there in the schedule Sa: r1(Y); r2(Y); w1(Y); r1(Z); w2(Y); w1(Z)
To determine the number of conflicts in the given schedule, we need to identify any read-write or write-write conflicts.
A read-write conflict occurs when one transaction reads a data item that another transaction writes. A write-write conflict occurs when two transactions write to the same data item.
Let's analyze the schedule step by step:
1. r1(Y): Transaction r1 reads data item Y.
- No conflict here.
2. r2(Y): Transaction r2 reads data item Y.
- There is a read-write conflict between r2(Y) and r1(Y) since r2 reads after r1 writes.
3. w1(Y): Transaction w1 writes to data item Y.
- No conflict here.
4. r1(Z): Transaction r1 reads data item Z.
- No conflict here.
5. w2(Y): Transaction w2 writes to data item Y.
- There is a write-write conflict between w2(Y) and w1(Y) since both transactions write to the same data item.
6. w1(Z): Transaction w1 writes to data item Z.
- No conflict here.
In the given schedule, there are 2 conflicts: 1 read-write conflict (r2(Y) and r1(Y)) and 1 write-write conflict (w2(Y) and w1(Y)).
In summary, the schedule Sa: r1(Y); r2(Y); w1(Y); r1(Z); w2(Y); w1(Z) has 2 conflicts.