Conflict Serializable Schedule | View Serializability | Part 5 | DBMS | 306 скачать в хорошем качестве

Conflict Serializable Schedule | View Serializability | Part 5 | DBMS | 306

Playlist for all videos on this topic:    • Database Management System - DBMS (COMPUTE...   Conflict and View Serializability in DBMS As discussed in Concurrency control, serial schedules have less resource utilization and low throughput. To improve it, two or more transactions are run concurrently. But concurrency of transactions may lead to inconsistency in database. To avoid this, we need to check whether these concurrent schedules are serializable or not. Conflict Serializable: A schedule is called conflict serializable if it can be transformed into a serial schedule by swapping non-conflicting operations. Conflicting operations: Two operations are said to be conflicting if all conditions satisfy: They belong to different transactions They operate on the same data item At Least one of them is a write operation View Serializability A schedule will view serializable if it is view equivalent to a serial schedule. If a schedule is conflict serializable, then it will be view serializable. The view serializable which does not conflict serializable contains blind writes. View Equivalent Two schedules S1 and S2 are said to be view equivalent if they satisfy the following conditions: 1. Initial Read An initial read of both schedules must be the same. Suppose two schedule S1 and S2. In schedule S1, if a transaction T1 is reading the data item A, then in S2, transaction T1 should also read A. DBMS View Serializability Above two schedules are view equivalent because Initial read operation in S1 is done by T1 and in S2 it is also done by T1. 2. Updated Read In schedule S1, if Ti is reading A which is updated by Tj then in S2 also, Ti should read A which is updated by Tj. DBMS View Serializability Above two schedules are not view equal because, in S1, T3 is reading A updated by T2 and in S2, T3 is reading A updated by T1. 3. Final Write A final write must be the same between both the schedules. In schedule S1, if a transaction T1 updates A at last then in S2, final writes operations should also be done by T1. DBMS View Serializability Above two schedules is view equal because Final write operation in S1 is done by T3 and in S2, the final write operation is also done by T3.