Common questions

Why do we make any pair of transaction serially equivalent?

Why do we make any pair of transaction serially equivalent?

Serial Equivalence Recall, write/write and read/write are conflicting. Read/read operations are not conflicting. For two transactions to be serially equivalent, all pairs of conflicting operations must execute in the same order on all objects they both access.

How many view equivalent serial schedules are possible?

2 view equivalent serial schedules
Now, in this question there is blind write by T1 and T3. so in total there are 2 view equivalent serial schedules are possible where last operation T5T6 is fixed.

What is Serializability How can Serializability be ensured?

Serializability is the classical concurrency scheme. It ensures that a schedule for executing concurrent transactions is equivalent to one that executes the transactions serially in some order. It assumes that all accesses to the database are done using read and write operations.

What is conflict equivalence?

Conflict Equivalent: Two schedules are said to be conflict equivalent when one can be transformed to another by swapping non-conflicting operations. Note 2: The schedule which is conflict serializable is always conflict equivalent to one of the serial schedule.

Which history is equivalent to a serial history?

Now observe that each pair of conflicting operations in the given history is in the same order as in the serial history, because the pair corresponds to an edge in the graph. Since all conflicting operations are in the same order, the given history is equivalent to the serial history.

Which object is used to commit or abort transaction?

Transaction object
The Transaction object is the handle for a transaction. Methods off the transaction handle are used to configure, abort and commit the transaction.

When two transactions occur at same time and wait for each other to be completed this phase is called?

Two Phase Locking Protocol also known as 2PL protocol is a method of concurrency control in DBMS that ensures serializability by applying a lock to the transaction data which blocks other transactions to access the same data simultaneously.

What are two aspects Serializability?

Types of Serializability

  • Result Equivalent Schedule. Two schedules, S1 and S2 are said to result equivalent if they produce the same output obtained when the schedules are serially executed.
  • Conflict Equivalent Schedule.
  • View Equivalent Schedule.

What are the two aspects of serializability?

Serializability helps preserve the consistency and concurrency of a database. There are 2 methods widely used to check serializability i.e. Conflict equivalent and View equivalent.

What is result equivalence?

It is also known as Result Equivalent Schedule. Two schedules S1 and S2 are said to be result equivalent if they produce the same final database state, in other words, they must produce the same result after execution.