Database transaction:
In database, a database transaction is a logical unit of database operations
which are executed as a whole to process user requests for retrieving data or
updating the database.
Transaction should have four properties:
(i) Atomicity
(ii) Consistency
(iii) Isolation
(iv) Durability
(i) Atomicity: A
transaction is an indivisible unit. It is included in all operations or have
done or not done.
(ii) Consistency: Transaction
must keep the database from one consistent state to another consistent state
variable. Consistency is closely related 
to atomicity.
to atomicity.
(iii) Isolation: 
A transaction is
implemented and cannot be interfered with by other transactions. That is, an
internal operation of a transaction and the use of the data is isolated with
other transaction, the concurrent implementation of all transactions can not
interfere between with each other.
A transaction is
implemented and cannot be interfered with by other transactions. That is, an
internal operation of a transaction and the use of the data is isolated with
other transaction, the concurrent implementation of all transactions can not
interfere between with each other.
(iv) Durability: It
is also called permanence. It refers to a transaction which is submitted, and
the in the database it charges should be permanent. The next operation or other
faults should not have any impact on them.
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