Here are the key concepts of transaction processing in Relational Database Management Systems (RDBMS):

1. Transaction:

A transaction is a logical unit of work that represents a sequence of database operations. These operations can include reading, writing, or modifying data in the database. A transaction is typically initiated by a user or an application and should maintain the ACID properties (Atomicity, Consistency, Isolation, Durability).

2. ACID Properties:

ACID is an acronym that stands for:

- Atomicity: A transaction is atomic, meaning that it is treated as an indivisible unit of work. Either all the operations in a transaction are executed successfully, or none of them take effect. If any part of the transaction fails, the entire transaction is rolled back, and the database is restored to its previous state.
- Consistency: Transactions maintain the integrity and validity of the database by enforcing a set of predefined rules or constraints. These rules ensure that the database remains in a consistent state before and after a transaction.
- Isolation: Transactions are executed in isolation from each other to prevent interference or conflicts. The changes made by one transaction are not visible to other transactions until the changes are committed. Isolation levels, such as Read Uncommitted, Read Committed, Repeatable Read, and Serializable, define the level of isolation and concurrency control in the database.
- Durability: Once a transaction is committed, its changes are permanently saved in the database, even in the event of system failures or power outages. The changes are durable and can be recovered later.

3. Transaction States:

Transactions in an RDBMS go through different states during their lifecycle. The common transaction states are:

- Active: The transaction is actively executing and performing database operations.
- Partially Committed: The transaction has executed all its operations, and the changes are yet to be made permanent.
- Committed: The transaction has successfully completed all its operations, and the changes are made permanent in the database.
- Aborted: The transaction has encountered an error or failure and is rolled back, undoing any changes made.
- Failed: The transaction has encountered an unrecoverable error, and the system cannot proceed with it. It requires manual intervention or recovery.

4. Transaction Control Statements:

RDBMS provides transaction control statements to manage transactions effectively. These statements include:

- BEGIN TRANSACTION/START TRANSACTION: Starts a new transaction.
- COMMIT: Marks the successful completion of a transaction and makes the changes permanent in the database.
- ROLLBACK: Aborts a transaction and undoes any changes made.
- SAVEPOINT: Sets a savepoint within a transaction, allowing partial rollback to that point if needed.
- SET TRANSACTION: Sets various transaction properties, such as isolation level.

These concepts form the foundation of transaction processing in RDBMS. By ensuring atomicity, consistency, isolation, and durability, transactions provide a reliable and robust mechanism for interacting with and managing data in a database.

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