ACID Properties in DBMS :-

➺ Transaction is a single logical unit of a program that changes the contents of a database. It can access data by read and write operations.

➺ The database can be changed from one consistent state to another after the completion of a transaction.

➺ DBMS Followed four primary properties in order to ensure consistency, completeness, and integrity of any database, before and after a transaction. These are called ACID properties.

◆ DBMS has four Properties:-

A - Atomicity

C - Consistency

I - Isolation

D - Durability

➺ It refers to the execution of a transaction completely or does not execute it at all.
➺ The transaction cannot be executed partially. A transaction is a single unit of a program and it must execute completely or not execute at all.
➺ Atomicity is also called the "All or Nothing Rule".

◆There are following two operations:-

○ Commit

➺ In this transaction Changes made to the database are visible to the user.

○ Abort

➺ In this transaction Changes made to the database are not visible to the user.

➺ For example, An online payment application that transfers money from one account to another and money is debited successfully from one account, the corresponding credited money to the other account.

➺ Ex:- Aakash transferred 200 rupees from his total balance of 700 to Rahul's a/c and before Rahul's balance was 100 after the transfer total balance is 300:-

     Before ➺               aakash                    rahul
                              700                       100
                            700-200                  100+200  
     After ➺                 500                       300

➺ Once the transaction is executed it should move from one consistent state to another.
➺ In order to maintain data integrity constant the database should remain in a consistent state before and after transaction completion.
➺ If the database was in an inconsistent state before the execution of a transaction, Then it will remain inconsistent state after the execution of the transaction as well.

➺ The total amount before and after the transaction must be the same.

➺ Ex. -  Aakash = 700 - 200 = 500
          Rahul = 100 + 200 = 300
   
          Before total is 800
          After total is 800 

➺ It is called consistency of data.

➺ More than one transaction can be executed parallelly. Multiple transactions occur independently without interference.
➺ Any changes that occur in a particular transaction would never be visible to other transactions until the change in the particular transaction has been committed or written in memory.

➺ Once the transaction completed its execution process after that, the changes and updates in the database should be saved permanently even in case of system failure, and get stored in non-volatile memory.

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