What is a transaction and what are ACID properties?
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Answer Posted / archana
A transaction is an atomic unit of work that must be
completed in its entirety.The transaction succeeds if it
committed and fails if it is aborted.Transactions have four
essential properties:atomicity,consistency,isolation, and
durability(known as the ACID properties).
Atomicity:The work cannot be broken into smaller
parts.Although a transaction might contain many SQL
statements,it must be run as all-or-nothing
proposition,which means that,if a transaction is only
partially complete when an error occurs,the work revertss
to its state prior to the start of the transaction.
Consistency:A transaction must operate on a consistent view
of the data and also leave the data in a consistency
state.Any work in progress must not be visible to other
transactions until the transaction has been committed.
Isolation:A transaction should appear to be running by
itself,the effects of other ongoing transactions must be
invisible to this transaction,and the effects of this
transaction must be invisible to other ongoing transaction.
Durability:When the transaction is committed,it must be
persisted so it is not lost in the event of a power
failure.Only committed transaction are recovered during
power-up and crash recovery;uncommitted work is roll back.
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