What Is a Transaction?
In a database, a transaction is a sequence of operations that are treated as a single unit of work. A transaction typically involves a set of operations that manipulate the database, such as inserting or updating data. These operations are treated as a single unit, meaning that they must all be completed successfully for the transaction to be considered successful. If any part of the transaction fails, the entire transaction is rolled back, and the database is restored to its previous state. Transactions provide a way to ensure that database operations are reliable, predictable, and recoverable, making them a fundamental tool in modern database design.
What are ACID Transactions?
ACID transactions are a set of properties that are used to guarantee the reliability and integrity of database transactions. In other words, they provide a way to ensure that all changes made to a database either occur in their entirety or not at all.
In practical terms, this means that if a transaction is interrupted or stopped, any changes made by the transaction are rolled back to their previous state. This ensures that the database remains in a consistent state and prevents any data inconsistencies.
ACID transactions have become an essential tool for database designers and developers, as they ensure that data is processed reliably and predictably. They are a fundamental part of modern databases, and their use has helped to make databases more robust and reliable than ever before.
ACID Transaction Properties
ACID transactions are based on four core properties: atomicity, consistency, isolation, and durability.
- Atomicity - This property ensures that a transaction is treated as a single unit of work. The entire transaction is either completed successfully or not at all.
- Consistency - This property ensures that the database remains in a valid state before and after each transaction. It requires that the transaction abides by any constraints or validations that have been set up by the database administrator. This helps prevent data inconsistencies and ensures data accuracy.
- Isolation - This property ensures that multiple transactions can be executed concurrently, without interfering with each other. The database uses various isolation levels to ensure that transactions are isolated from one another and that concurrent transactions do not conflict. This helps prevent dirty reads, non-repeatable reads, and phantom reads.
- Durability - This property ensures that once a transaction has been committed, the changes made by that transaction will persist even if there is a system failure or a power outage. This is achieved by writing transaction logs to disk or other non-volatile storage so that the database can be restored to its state before the failure occurred.
How ACID Transactions Work
Once an ACID transaction has been initiated, the operations are executed in a particular order. During this execution process, the database records every change made by the transaction, along with any actions needed to undo those changes.
If a transaction completes successfully, all of its changes are permanently written into the database. If any operation within the transaction fails, the entire transaction is rolled back, and the database is returned to its state from before the transaction began.
ACID Transaction Examples
ACID transactions are used in a wide variety of applications and industries. Examples include:
- Banking - ACID transactions are used in banking to ensure that deposits, withdrawals, and money transfers are processed correctly, and that account balances remain accurate.
- Healthcare - In healthcare ACID transactions are used for changes to patient records to maintain accuracy and confidentiality. ACID transactions also keep medical records consistent and up-to-date, enabling physicians and other medical professionals to make informed decisions.
- E-commerce - In the e-commerce industry, ACID transactions are used to confirm that inventory levels are maintained accurately, that orders are processed correctly, and that payment transactions are secure and accurate.
