ACID (Atomicity , Consistency , Isolation , Durability ). Atomicity Consistency Isolation Durability (ACID) is a concept referring to a database system’s four transaction properties: atomicity, consistency, isolation and durability.
Here either all the statements (whether an update, delete or insert) of the transaction will happen or not happen. To guarantee atomicity, SQL Server uses a Write Ahead Transaction Log. The log always gets written to first before the associated data changes. That way, if and when things go wrong, SQL Server will know how to rollback to a state where every transaction happened or didn’t happen.
A transaction reaching its normal end, thereby committing its results, preserves the consistency of the database. If something bad happens then everything in the transaction will be rolled back. After each transaction DB should be in a consistent state.
Events happening within a transaction must be hidden from other transactions running concurrently.
Once a transaction has been completed and has committed its results to the database, the system must guarantee that these results survive any subsequent malfunctions.
All the four things are very important when you are dealing with the databases.