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What is Transaction in DBMS?

A transaction can be described as a group of tasks. 

Features of Transaction:
1. In Transaction, a single task is the lowest processing unit which cannot be further divided.
2. Transaction is a very small unit of a program and it may include several low-level tasks. 
3. A transaction in a database system must preserve Atomicity, Consistency, Isolation, and Durability generally regarded as ACID in order to ensure data integrity, accuracy and completeness.

What is Serializability in DBMS?

Serializability in DBMS Identifies data transactions as occurring serially and sequentially, independent of one another, even though they may have occurred concurrently.
It is the process or procedure of serial and sequential arrangements so that when multiple transactions are being performed by the operating system in a multiprogramming environment, there are possibilities that instructions of one transaction are rendered with some other transaction.

1. Sequential Schedule: This is sequential execution order of a transaction. A schedule can have many transactions in it, each consisting of a number of instructions or tasks.

2. Serial Schedule: Transactions here are associated in such a way that one transaction is performed first, so that when the first transaction completes its cycle, then the next transaction is performed. 

States of Transactions

1. Active: During this state, the transaction is being executed. 

2. Partially Committed: When a transaction performs its final operation, it is said to be in a partially committed state.

3. Failed: A transaction is said to be in a failed state if any of the checks conducted by the database recovery system fails.

4. Aborted: If any of the checks fails and the transaction has reached a failed state, then the recovery manager rolls back all its write operations on the database to bring the database back to its original state where it was prior to the execution of the transaction.

The database recovery module can select one of the two operations after a transaction aborts:
a. Re-start the transaction
b. Kill the transaction

5. Committed: If a transaction executes all its operations successfully, it is said to be committed and fully established on the database system.

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