Understanding Database Isolation Levels: Balancing Concurrency and Consistency

Introduction

In the world of database transactions, there are several levels of isolation that can be used to control how transactions interact with one another. These levels are designed to balance the need for concurrency and performance with the need for consistency and accuracy. In this article, we will discuss the five isolation levels defined by the ANSI SQL standard: Read Uncommitted, Read Committed, Repeatable Read, Serializable, and Snapshot.

Overview of the Five Isolation Levels:

1. Read Uncommitted: In this isolation level, transactions are not required to lock rows before reading or writing data. This means that a transaction can read data that has been modified by another uncommitted transaction. This can lead to non-repeatable reads and phantom reads. However, it provides the highest level of concurrency and can be useful in certain situations.

• Example: Transaction A is updating a row in Table X, and Transaction B reads the same row before Transaction A commits the change. Transaction B can see the uncommitted data from Transaction A.
• Locking behavior: No lock at all. Transactions can read uncommitted data from other transactions.