Serializability In DBMS

As we know, some non-serial schedules are also consistent and behave like serial schedules. The concept of Serializability is used to check whether the given non-serial schedule is serial or not.

According to Serializability 

“If a given non-serial schedule of ‘n’ transactions is equivalent to some serial schedule of ‘n’ transactions, then it is called a serializable schedule.”

Example of Serializability

Suppose there are 3 transactions (T1, T2, T3) where T1 executes first and then T2 and T3. Then, the serial schedule will contain the following series of transaction executions.

T1→T2→T3

Non-serial must contain a series where any transaction cannot repeat itself, just like the above serial schedule, but the position of the transaction can be interchanged. So, Non-serial will be one of the following if it is serializable.

• T1→T2 →T3
• T1→T3 →T2
• T2→T1 →T3
• T2→T3 →T1
• T3→T1 →T2
• T3→T2 →T1

If a schedule contains a series of transactions where transactions are repeating, like T1→T2 →T1 →T3 where T1 is repeating, then that series will not be serial.

Types of Serializability

Serializability is mainly of two types

We will explain both topics in the next lecture.