Properties of Transactions--
The following are the ACID properties:
1. Atomicity: A transaction is an atomic unit of processing; it is either performed in its entirety or not performed at all.Either all operations of the transaction are reflected properly in the
database, or none are.
2. Consistency preservation: A transaction is consistency preserving if its complete execution take(s) the database from one consistent state to another.Execution of a transaction in isolation (that is, with no other
transaction executing concurrently) preserves the consistency of the database.
3. Isolation: A transaction should appear as though it is being executed in isolation from other transactions. That is, the execution of a transaction should not be interfered with by any other transactions executing concurrently.
Even though multiple transactions may execute concurrently, the
system guarantees that, for every pair of transactions Ti and Tj , it appears
to Ti that either Tj finished execution before Ti started, or Tj started execution
after Ti finished. Thus, each transaction is unaware of other transactions
executing concurrently in the system.
4. Durability or permanency: The changes applied to the database by a committed transaction must persist in the database. These changes must not be lost because of any failure.
After a transaction completes successfully, the changes it has made
to the database persist, even if there are system failures.
The following are the ACID properties:
1. Atomicity: A transaction is an atomic unit of processing; it is either performed in its entirety or not performed at all.Either all operations of the transaction are reflected properly in the
database, or none are.
2. Consistency preservation: A transaction is consistency preserving if its complete execution take(s) the database from one consistent state to another.Execution of a transaction in isolation (that is, with no other
transaction executing concurrently) preserves the consistency of the database.
3. Isolation: A transaction should appear as though it is being executed in isolation from other transactions. That is, the execution of a transaction should not be interfered with by any other transactions executing concurrently.
Even though multiple transactions may execute concurrently, the
system guarantees that, for every pair of transactions Ti and Tj , it appears
to Ti that either Tj finished execution before Ti started, or Tj started execution
after Ti finished. Thus, each transaction is unaware of other transactions
executing concurrently in the system.
4. Durability or permanency: The changes applied to the database by a committed transaction must persist in the database. These changes must not be lost because of any failure.
After a transaction completes successfully, the changes it has made
to the database persist, even if there are system failures.
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