Serializable isolation in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Serializable isolation in databases?

Serializable isolation is the highest level of transaction isolation. It ensures transactions appear to run one after another, preventing conflicts and anomalies.

intermediate

How does PostgreSQL implement Serializable isolation?

PostgreSQL uses Serializable Snapshot Isolation (SSI), which detects conflicts between transactions and aborts one to keep the system consistent.

intermediate

What happens if two transactions conflict under Serializable isolation in PostgreSQL?

One transaction will be aborted with a serialization failure error. The application should retry the transaction to maintain correctness.

beginner

Why is Serializable isolation considered safer than Read Committed or Repeatable Read?

Because it prevents all anomalies like dirty reads, non-repeatable reads, phantom reads, and write skew by ensuring transactions behave as if run one by one.

beginner

What is a common real-life analogy for Serializable isolation?

Imagine a single cashier serving customers one at a time, so no two customers can interfere with each other's orders. This avoids mistakes and confusion.

Which isolation level guarantees transactions behave as if executed one after another?

A Repeatable Read

B Serializable

C Read Committed

D Read Uncommitted

Serializable isolation ensures transactions appear sequential, preventing anomalies.

In PostgreSQL, what happens when two concurrent transactions conflict under Serializable isolation?

A One transaction is aborted with a serialization failure

B Both transactions commit successfully

C Both transactions are rolled back automatically

D The database locks the entire table

PostgreSQL aborts one conflicting transaction to maintain serializability.

What technique does PostgreSQL use to implement Serializable isolation?

A Two-phase locking

B Write-ahead logging

C Read Uncommitted reads

D Serializable Snapshot Isolation (SSI)

PostgreSQL uses SSI to detect conflicts and ensure serializable behavior.

Which of these anomalies is prevented by Serializable isolation?

A Phantom reads

B Non-repeatable reads

C All of the above

D Dirty reads

Serializable isolation prevents all these anomalies by enforcing strict transaction order.

If a transaction is aborted due to serialization failure, what should the application do?

A Retry the transaction

B Ignore and continue

C Rollback the entire database

D Switch to Read Uncommitted isolation

Retrying the transaction is the correct way to handle serialization failures.

Explain how Serializable isolation works in PostgreSQL and why it is important.

Think about how PostgreSQL keeps transactions from interfering with each other.

Describe a real-life example that helps understand Serializable isolation.

Imagine a situation where only one person can be served at once.