What is a transaction and what are ACID properties?

Answer Posted / hloni

A transaction is a sequence of database operations that
access the database. It must be a logical unit of work,
meaning that no portion of the transaction can exist on its
own. Either all parts are executed or the transaction is
aborted.

Transaction has five main properties called ACIDS:

1. Atomicity -- all parts of the transaction are executed
or else the transaction is aborted.

2. Consistency -- indicates the permanence of the
database's consistent state. When a transaction is
completed the database reaches a consistence state.

3. Isolation -- means that the data used during the
exercution of a transaction cannot be used by the a second
transaction until the first transaction is complete.

4. Durability -- ensures that once transaction changes are
commited, they cannot be lost even in the event of system
failure.

5. Serializability -- ensures that concurrent execution of
several transaction yields consistent results. This
property is important in a multi-user and distributed
datbases, where multiple transaction are likely to be
executed concurrently.

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