In Oracle database system, in addition to store the data permanently into the storage devices there is one most important thing that oracle has to maintain in their database system is the consistency of the data. So that the end user will get the consistent image of the data and for that ACID property plays an important role.
The ACID property is an abbreviation of Atomicity, Consistency, Isolation and durability and it's used to maintain the database consistency.
Atomicity: The first property is the atomicity which means that either the transaction will be completely successfully or completely aborted. For e.g. if we’re transferring money from one back account to another bank account then the transfer will completely successful or completely fail.
Consistency: Since oracle support multiple concurrently versions
of a transaction so to maintain the data consistency is one of the concerns
that oracle has to manage and for that it uses the feature of undo tablespace. For e.g. if user A update salary of an employee whose
employee ID is 100 in emp table but the transaction is yet to be committed by the
user and during the same time user B trying to access the same data set then in
order to maintain the data consistency the oracle create a past image of the
data block from undo data and provide a consistent dataset to the user.
Isolation: since each and every transaction work independently so they must be done in isolation and for that oracle provide the locking and enqueue mechanism so that multiple concurrent operation which are modifying the same data set will not lead the data to either corruption or inconsistency. For e.g. if any user will update the data then using the locking mechanism oracle will ensure that during the same time no other user will either update the same value or will be able to drop the table until the first user will commit or rollback its transaction.
Durability: Since the data must be store somewhere in a storage
device so that it can be persistent even after shutting down the database or in
the event of database failure, so oracle provide the feature of datafile where the data are basically basically store into the storage device which are persistent in
nature.
