Conflicting actions

Two or more actions are said to be in conflict if:
The actions belong to different transactions.
At least one of the actions is a write operation.
The actions access the same object (read or write).

The following set of actions is conflicting:
T1:R(X), T2:W(X), T3:W(X)

While the following sets of actions are not:
T1:R(X), T2:R(X), T3:R(X)
T1:R(X), T2:W(Y), T3:R(X)

Conflict equivalence

The schedules S1 and S2 are said to be conflict-equivalent if the following conditions are satisfied:
Both schedules S1 and S2 involve the same set of transactions (including ordering of actions within each transaction).
The order of each pair of conflicting actions in S1 and S2 are the same.


A schedule is said to be conflict-serializable when the schedule is conflict-equivalent to one or more serial schedules.

Another definition for conflict-serializability is that a schedule is conflict-serializable if and only if there exists an acyclic precedence graph/serializability graph for the schedule.