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Conflict Serializable Schedule

  • A schedule is called conflict serializability if after swapping of non-conflicting operations, it can transform into a serial schedule.
  • The schedule will be a conflict serializable if it is conflict equivalent to a serial schedule.

Conflicting Operations

The two operations become conflicting if all conditions satisfy:

  1. Both belong to separate transactions.
  2. They have the same data item.
  3. They contain at least one write operation.

Example:

Swapping is possible only if S1 and S2 are logically equal.


DBMS Conflict Serializable Schedule

Here, S1 = S2. That means it is non-conflict.


DBMS Conflict Serializable Schedule

Here, S1 ≠ S2. That means it is conflict.

Conflict Equivalent

In the conflict equivalent, one can be transformed to another by swapping non-conflicting operations. In the given example, S2 is conflict equivalent to S1 (S1 can be converted to S2 by swapping non-conflicting operations).

Two schedules are said to be conflict equivalent if and only if:

  1. They contain the same set of the transaction.
  2. If each pair of conflict operations are ordered in the same way.

Example:


DBMS Conflict Serializable Schedule

Schedule S2 is a serial schedule because, in this, all operations of T1 are performed before starting any operation of T2. Schedule S1 can be transformed into a serial schedule by swapping non-conflicting operations of S1.

After swapping of non-conflict operations, the schedule S1 becomes:

T1 T2
Read(A)
Write(A)
Read(B)
Write(B)




Read(A)
Write(A)
Read(B)
Write(B)

Since, S1 is conflict serializable.






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