* Atomicity: Each transaction is said to be "atomic." If one part of the transaction fails, the entire transaction fails. Modifications on the data in the database either fail or succeed.
* Consistency: This property ensures 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.
* Isolation: It requires that multiple transactions occurring at the same time not impact each other's execution.
* Durability: It ensures that any transaction committed to the database will not be lost.
Atomicity: cannot be divided into smaller work units.
Concurrency: more than one transaction can occur at a time.
Isolation: one transaction has limited knowledge about changes made by another.
Durability: the transaction makes persistent changes.
If you are unable to do something properly for the first time, call it Version 1.0!
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A transaction is an atomic unit of work that must be completed in its entirety.The transaction succeeds if it committed and fails if it is aborted.Transactions have four essential properties:atomicity,consistency,isolation, and durability(known as the ACID properties).
Atomicity:The work cannot be broken into smaller parts.Although a transaction might contain many SQL statements,it must be run as all-or-nothing proposition,which means that,if a transaction is only partially complete when an error occurs,the work revertss to its state prior to the start of the transaction.
Consistency:A transaction must operate on a consistent view of the data and also leave the data in a consistency state.Any work in progress must not be visible to other transactions until the transaction has been committed.
Isolation:A transaction should appear to be running by itself,the effects of other ongoing transactions must be invisible to this transaction,and the effects of this transaction must be invisible to other ongoing transaction.
Durability:When the transaction is committed,it must be persisted so it is not lost in the event of a power failure.Only committed transaction are recovered during power-up and crash recovery;uncommitted work is roll back.
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1) Atomicity: Either all operations of the transaction are reflected properly in the database or none are.
2) Consistency: Transactions must preserve the internal consistency and integrity of the database. If the database satisfies all of its integrity constraints before the transaction, it must also satisfy those conditions after the transaction.
3) Isolation: It requires that multiple transactions occurring at the same time not impact each other's execution.
4) Durability: After a transaction completes successfully, the changes it has made to the database persist, even if there are system failures.
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Microsoft MVP (ASP.Net/IIS)
The ACID model is one of the oldest and most important concepts of database theory. It sets forward four goals that every database management system must strive to achieve: atomicity, consistency, isolation and durability. No database that fails to meet any of these four goals can be considered reliable.
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.
Only valid data (valid according to integrity constraints) may be commited.
One transaction does not interfere with another. The 'executor' of a transaction has the feeling that he has the entire database for himeself.
A commited transaction will not be lost.
Technical detail of ACID: Oracle uses the redo log and undo to make ACID possible.