Part 126: Isolation Levels: Repeatable Read & Serializable

The strictest isolation levels for financial and mission-critical systems.

1. Repeatable Read (Default in MySQL InnoDB)

• Guarantees that any row read during the transaction returns the exact same snapshot throughout the entire transaction.

2. Serializable (The Highest Isolation Level)

• Transactions behave as if executed completely sequentially, one at a time.
• Completely prevents phantom reads and serialization anomalies.
• Trade-off: High serialization conflict rate (transactions must implement retry loops on serialization failure errors).

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

Key Takeaways

• Use SERIALIZABLE for financial balances where conflict checks must be mathematically airtight.

In Part 127, we explore Database Locking Mechanisms: Shared (S) vs Exclusive (X) Locks!