Sql Server

Question

How is acid property related to data base.

Satyapriya Nayak · Answer

Hi Sharad Normal 0 A transaction is a sequence of operations performed as a single logical unit of work. A logical unit of work must exhibit four properties called the ACID (Atomicity Consistency Isolation and Durability) properties to qualify as a transaction: Atomicity A transaction must be an atomic unit of work; either all of its data modifications are performed or none of them is performed. Consistency When completed a transaction must leave all data in a consistent state. In a relational database all rules must be applied to the transaction's modifications to maintain all data integrity. All internal data structures such as B-tree indexes or doubly-linked lists must be correct at the end of the transaction. Isolation Modifications made by concurrent transactions must be isolated from the modifications made by any other concurrent transactions. A transaction either sees data in the state it was in before another concurrent transaction modified it or it sees the data after the second transaction has completed but it does not see an intermediate state. This is referred to as serializability because it results in the ability to reload the starting data and replay a series of transactions to end up with the data in the same state it was in after the original transactions were performed. Durability After a transaction has completed its effects are permanently in place in the system. The modifications persist even in the event of a system failure. Thanks

Santhosh Kumar Jayaraman · Answer

ACID stands for Atomicity Consistency Isolation Durablity Atomicity Modification on the data in the database either fail or succeed. The beginning of such a modification starts with a transaction and ends when a transaction finishes (either by a commit or a rollback ). A software crash entails an implicit rollback. Consistency Only valid data (valid according to integrity constraints ) may be commited. Isolation One transaction does not interfere with another. The 'executor' of a transaction has the feeling that he has the entire database for himeself. Durablity A commited transaction will not be lost. source:http://www.adp-gmbh.ch/misc/databases/acid.html