SQL Transactions: Understanding Transaction Isolation Levels

Read Uncommitted

The lowest isolation level where transactions can see uncommitted changes from others.

This can lead to dirty reads and is rarely used in production.

• Allows maximum concurrency.
• Risk of reading inconsistent data.

Read Committed

Prevents dirty reads by only reading committed data.

However, non-repeatable reads and phantom reads can still occur.

• Default in many database systems.
• Balances consistency and concurrency.

Repeatable Read

Ensures that if a transaction reads data twice, it will see the same data each time.

Prevents dirty and non-repeatable reads but phantom reads can still happen.

• Useful for consistent reads within a transaction.
• May reduce concurrency due to locking.

Serializable

The highest isolation level that ensures complete isolation between transactions.

Prevents dirty reads, non-repeatable reads, and phantom reads by serializing transactions.

• Ensures full consistency.
• Can significantly reduce concurrency and increase locking.

Setting Isolation Level Example

Here is how you set the isolation level to Repeatable Read in SQL: