ACID Properties of RDBMS

 Hii guys, I hope you are doing great, Today here I am going to explain you about the ACID properties of RDBMS and its types.

Transaction-

Any operation that reads from or writes to a database is referred to as a transaction in relational databases.

A transaction is a logical unit of work that can only have one of two possible outcomes: it can either be fully completed or completely abandoned.

The database is changed from one consistent state to another by a successful transaction, and a consistent database state is one in which all data integrity constraints are met.

State of Transaction-

DBMS transaction states. In DBMS, a transaction is a group of logically connected activities. The various states that a transaction can be in at any given time in a DBMS are known as transaction states. There are six different transaction states: active, committed, committed partially, failed, aborted, and terminated.

Fig.1

Property of Transaction-

The transaction has the four properties. These are used to maintain consistency in a database, before and after the transaction.

Atomicity

Consistency

Isolation

Durability

Atomicity-

It states that all operations of the transaction take place at once if not, the transaction is aborted.

There is no midway, i.e., the transaction cannot occur partially. Each transaction is treated as one unit and either run to completion or is not executed at all.
Atomicity involves the following two operations:

Abort: If a transaction aborts, then all the changes made are not visible.

Commit: If a transaction commits, then all the changes made are visible.

For ex- In an application that transfers funds from one account to another, the atomicity property ensures that, if a debit is made successfully from one account, the corresponding credit is made to the other account.  

Consistency-

The integrity constraints are maintained so that the database is consistent before and after the transaction.

The execution of a transaction will leave a database in either its prior stable state or a new stable state.

The consistent property of database states that every transaction sees a consistent database instance.

For ex- In an application that transfers funds from one account to another, the consistency property ensures that the total value of funds in both the accounts is same at the start and end of each transaction. 

Isolation-

It shows that the data which is used at the time of execution of a transaction cannot be used by the second transaction until the first one is completed.

In isolation, if the transaction T1 is being executed and using the data item X, then that data item can't be accessed by any other transaction T2 until the transaction T1 ends.
The concurrency control subsystem of the DBMS enforced the isolation property.

For ex- In an application that transfers funds from one account to another, the isolation property ensures that another transaction sees the transferred funds in one account or the other, but not in both, nor in neither.

Durability-

The durability property is used to indicate the performance of the database's consistent state. It states that the transaction made the permanent changes.

They cannot be lost by the erroneous operation of a faulty transaction or by the system failure. When a transaction is completed, then the database reaches a state known as the consistent state. That consistent state cannot be lost, even in the event of a system's failure.

The recovery subsystem of the DBMS has the responsibility of Durability property.

For ex- In an application that transfers funds from one account to another, the durability property ensures that the changes made to each account will not be reversed.