Isolation levels in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of isolation levels in a database?

Isolation levels control how transaction changes are visible to other transactions, helping to prevent problems like dirty reads, non-repeatable reads, and phantom reads.

beginner

Name the four standard isolation levels defined by SQL.

The four standard isolation levels are:<br>1. Read Uncommitted<br>2. Read Committed<br>3. Repeatable Read<br>4. Serializable

intermediate

What problem does the Read Uncommitted isolation level allow?

Read Uncommitted allows dirty reads, meaning a transaction can see uncommitted changes made by other transactions.

intermediate

Explain the difference between Repeatable Read and Serializable isolation levels.

Repeatable Read prevents dirty and non-repeatable reads but may allow phantom reads. Serializable is the strictest level, preventing dirty reads, non-repeatable reads, and phantom reads by making transactions appear fully isolated.

beginner

Which isolation level is the default in MySQL InnoDB engine?

The default isolation level in MySQL InnoDB is Repeatable Read.

Which isolation level allows a transaction to read uncommitted changes from another transaction?

A Read Uncommitted

B Read Committed

C Repeatable Read

D Serializable

Read Uncommitted allows dirty reads, meaning it can see uncommitted changes.

Which isolation level prevents dirty reads but allows non-repeatable reads?

A Read Uncommitted

B Read Committed

C Repeatable Read

D Serializable

Read Committed prevents dirty reads but does not prevent non-repeatable reads.

What problem does the Serializable isolation level prevent that Repeatable Read might not?

A Dirty reads

B Non-repeatable reads

C Phantom reads

D Lost updates

Serializable prevents phantom reads, which Repeatable Read may allow.

In MySQL InnoDB, what is the default isolation level?

A Repeatable Read

B Read Committed

C Read Uncommitted

D Serializable

MySQL InnoDB uses Repeatable Read as the default isolation level.

Which isolation level offers the highest data consistency but may reduce concurrency?

A Read Uncommitted

B Read Committed

C Repeatable Read

D Serializable

Serializable is the strictest isolation level, ensuring highest consistency but can reduce concurrency.

Describe the four standard isolation levels and the types of read phenomena they prevent.

Think about how each level controls visibility of changes between transactions.

Explain why the default isolation level in MySQL InnoDB is Repeatable Read and what benefits it provides.

Consider the trade-off between strictness and speed.