How does isolation maintain consistency in concurrent database transactions?

Isolation maintains consistency in concurrent database transactions by ensuring each transaction is executed separately without interference.

In more detail, isolation is one of the four key properties of database transactions, often referred to as ACID (Atomicity, Consistency, Isolation, Durability). The principle of isolation is crucial in a multi-user database environment where multiple transactions are often executed concurrently. Without isolation, the simultaneous execution of transactions could lead to data inconsistencies and conflicts.

Isolation works by creating a separate environment for each transaction. This means that the changes made by one transaction are not visible to other transactions until the first transaction is completed and committed. This prevents conflicts and ensures that each transaction does not affect others. For example, if two transactions are trying to modify the same data, isolation ensures that they are executed one after the other, not simultaneously. This way, the outcome of the transactions remains consistent, regardless of the order in which they are executed.

There are different levels of isolation, each providing a different balance between performance and data consistency. The highest level of isolation, serialisable, ensures absolute consistency by executing transactions one after the other. However, this can lead to performance issues in a busy system. Lower levels of isolation allow for more concurrency, but at the risk of potential inconsistencies, such as dirty reads, non-repeatable reads, and phantom reads.

Locking and versioning are two common techniques used to achieve isolation. Locking prevents other transactions from accessing data that is being used by a current transaction, while versioning allows each transaction to work with a snapshot of the data at a specific point in time.

In conclusion, isolation is a fundamental principle in database management systems that ensures data consistency in concurrent transactions. By creating a separate environment for each transaction and using techniques like locking and versioning, isolation prevents conflicts and maintains the integrity of the database.