Difference between Conflict and View Equivalent
Conflict Equivalence and Conflict Serializable Schedule
Conflict Equivalence :
Schedules are conflict equivalent if they can be transformed one into other by a sequence of non conflicting interchanges adjacent actions.
Conflict Serializable Schedule :
A Schedule is conflict serializable if it is conflict equivalent to any of serial schedule.
View Equivalent Schedule and View serializable schedule
View Equivalent Schedule :
Consider two schedules S1 and S2, they are said to be view equivalent if following conditions are true :
- Initial read must be same.
- There are two transactions say Ti and Tj, The schedule S1 and S2 are view equivalent if in schedule S1, Ti reads A that has been updated by Tj, and in schedule S2, Ti must read A from Tj. i.e. write-read(WR) sequence must be same between S1 and S2.
- Final write operations should be same between S1 and S2.
View serializable schedule :
A Schedule is view serializable if it is view equivalent to any serial schedule. The following two examples will illustrate how to find view equivalent schedule.
Difference Between Conflict Equivalent Schedule and View Equivalent Schedule
- Conflict serializability is easy to achieve but view serializability is difficult to achieve
- Every conflict serializable is view serializable but the reverse is not true.
- It is easy to test conflict serializability but expensive to test view serializability.
- Most of the concurrency control schemes used in practice are based on conflict serializability.
|Questions on View Serializable||Implementation of Transaction in SQL|
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