This is going to be a very quick post, mainly because so many people have asked me what ACID means.

This post applies to a lot of topics / modules; but mainly to Databases and Distributed Computing.

ACID

ACID is a set of properties that guarantee Database transactions are process reliably. The acronym stands for:

• Atomicity
• Consistency
• Isolation
• Durability

And this is what they all mean:

 

Atomicity

Atomicity states that all transactions follow the ‘all-or-nothing’ rule. That is, a transaction is said to be atomic, if when one part of the transaction fails, the entire transaction fails to process, and the database state is left unchanged.

 

Consistency

Consistency states that the database must remain in a consistent state. Therefore, if we execute a transaction, then the database must be taken from one consistent state into another consistent state.

 

Isolation

Isolation states that other operations cannot access or see data that has been modified by a transaction that is still yet to finish.

No transaction must be aware of other transactions that are running concurrently with it, that is, at the same time. However, one transaction may be forced to wait for another transaction to finish processing in order to access certain data.

 

Durability

Durability states that once a transaction has been completed, then the transaction will not be lost. That is, if the system should fail, then the data that the transaction modified should not be lost.

Durability does not imply a permanent state of the database. A subsequent transaction may modify data changed by a prior transaction without violating the durability principle.

 

References

http://en.wikipedia.org/wiki/ACID

Fundamentals of Databases book – the abstract of it that i have anyway, so i cant place a proper date or anything, sorry!

Google Define :D