Some Definitions concerning Transactions and Concurrency Control in Database

1. Serializability

Consider a set of transactions (T₁, T₂, …, T_n). S₁ is the state of database after they are concurrently executed and successfully completed and S₂ is the state of database after they are executed in any serial manner (one-by-one) and successfully completed. If S₁ and S₂ are same then  the database  maintains serializability.

2. Concurrent Execution

If more than one transactions are executed at the same time then they are said to be executed concurrently.

3. Recoverability

To maintain atomicity of database, undo effects of any transaction has to be performed in case of failure of that transaction. If undo effects successfully then that database maintains recoverability. This process  is known as  Rollback.

4. Cascading Rollback

If any transaction T_i is dependent upon T_j and T_j is failed due to any reason then rollback T_i. This is known as cascading rollback. Consider Figure 8.2. Here T₂ is dependent upon T₁ because T₂ reads value of C which is updated by T₁.

If T₁ fails then rollback T₁ and also T₂.

Source: Gupta Satinder Bal, Mittal Aditya (2017), Introduction to Basic Database Management System, 2nd Edition-University Science Press (2017)