ACID properties

Hi Sonakshi....





Thanks.....

hi... 
till now everybody has told you what theoretically an acid property is but It will be more clear if you Look at this example , in this example acid property is maintained else such transactions would get hectic.

BEGIN TRANSACTION

UPDATE ROADS SET TrafficDirection = 'Left'

WHERE Country = 'India';  

UPDATE TRAFFIC_LIGHTS

SET TrafficDirectionMode = 'Left'

WHERE Country = 'India';  

UPDATE INTERSECTIONS

SET TrafficDirectionConfigurationMode = 'Left'

WHERE Country = 'India';

 COMMIT

Hi Sonakshi,

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

 

Hi,

1.ACID (an acronymn for Atomicity Consistency Isolation Durability) is a concept that Database
 Professionals generally look for when evaluating databases and application architectures.
For a reliable database all this four attributes should be achieved.

Atomicity is an all-or-none proposition.

Consistency guarantees that a transaction never leaves your database in a half-finished state.

Isolation keeps transactions separated from each other until they're finished.

Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination.

please check below link for more information.

http://static-sa.rosiebarry.com/database/articles/acid_properties.html

Hope this will help you.

Thanks.

Hi Sonakshi,

i found below  explanation useful about ACID properties. have a look on it....


*Atomicity states that database modifications must follow an "all or nothing" rule. Each transaction is said to be "atomic." If one part of the transaction fails, the entire transaction fails. It is critical that the database management system maintain the atomic nature of transactions in spite of any DBMS, operating system or hardware failure.

* Consistency states that only valid data will be written to the database. If, for some reason, a transaction is executed that violates the database's consistency rules, the entire transaction will be rolled back and the database will be restored to a state consistent with those rules. On the other hand, if a transaction successfully executes, it will take the database from one state that is consistent with the rules to another state that is also consistent with the rules.

* Isolation requires that multiple transactions occurring at the same time not impact each other's execution. For example, if Joe issues a transaction against a database at the same time that Mary issues a different transaction, both transactions should operate on the database in an isolated manner. The database should either perform Joe's entire transaction before executing Mary's or vice-versa. This prevents Joe's transaction from reading intermediate data produced as a side effect of part of Mary's transaction that will not eventually be committed to the database. Note that the isolation property does not ensure which transaction will execute first, merely that they will not interfere with each other.

* Durability ensures that any transaction committed to the database will not be lost. Durability is ensured through the use of database backups and transaction logs that facilitate the restoration of committed transactions in spite of any subsequent software or hardware failures.

Thanks,
Pravin.