Read-only transactions in Spring Boot - Performance & Optimization

Performance: Read-only transactions

MEDIUM IMPACT

Read-only transactions reduce database locking and improve query performance, impacting server response time and user experience.

Executing database queries that only read data without modifying it

Spring Boot

@Transactional(readOnly = true)
public List<User> getUsers() {
    return userRepository.findAll();
}

Declares transaction as read-only, allowing database optimizations and avoiding write locks.

📈 Performance GainReduces lock contention and speeds up query execution, improving server response time.

Executing database queries that only read data without modifying it

Spring Boot

@Transactional
public List<User> getUsers() {
    return userRepository.findAll();
}

Default transactions are read-write, causing unnecessary locks and overhead even when no data changes.

📉 Performance CostIncreases database lock contention and query latency, blocking other operations.

Performance Comparison

Pattern	Database Locks	Transaction Overhead	Query Speed	Verdict
Read-write transaction for read-only query	High locks	Higher overhead	Slower	[X] Bad
Read-only transaction for read-only query	Minimal locks	Lower overhead	Faster	[OK] Good

Rendering Pipeline

Read-only transactions optimize backend database access, reducing server processing time before sending data to the frontend.

→Server Processing

→Database Query Execution

⚠️ BottleneckDatabase locking and transaction overhead

Core Web Vital Affected

INP

Read-only transactions reduce database locking and improve query performance, impacting server response time and user experience.

Optimization Tips

1Always mark transactions as read-only if no data modification is needed.

2Avoid default read-write transactions for simple read queries to reduce locking.

3Monitor database locks and query times to identify transaction overhead.

Performance Quiz - 3 Questions

What is the main benefit of marking a transaction as read-only in Spring Boot?

A It allows data to be modified faster.

B It reduces database locking and speeds up read queries.

C It disables transaction management entirely.

D It increases security by encrypting data.

DevTools: Spring Boot Actuator / Database Monitoring Tools

How to check: Enable SQL logging and monitor transaction types; check database lock statistics during query execution.

What to look for: Look for reduced lock wait times and faster query completion when using read-only transactions.

Practice

1. What is the main purpose of using @Transactional(readOnly = true) in Spring Boot?

easy

A. To allow data modifications within the transaction

B. To optimize performance by indicating the method only reads data

C. To disable transaction management entirely

D. To automatically commit changes after method execution

Solution

1. Step 1: Understand the role of read-only transactions

   Read-only transactions tell Spring the method will only read data, not modify it.

2. Step 2: Recognize performance benefits

   This allows Spring and the database to optimize the transaction for reading, improving performance.

3. Final Answer:

   To optimize performance by indicating the method only reads data -> Option B

4. Quick Check:

   Read-only = optimize read performance [OK]

Hint: Read-only means no data changes allowed, just reading [OK]

Common Mistakes:

• Thinking readOnly=true allows data changes
• Confusing readOnly with disabling transactions
• Assuming it commits changes automatically

2. Which of the following is the correct way to declare a read-only transaction on a method in Spring Boot?

easy

A. @Transactional(readOnly = true)

B. @Transactional(readOnly)

C. @Transactional(enabled = true)

D. @Transactional(readOnly = false)

Solution

1. Step 1: Recall the correct syntax for read-only transactions

   The correct attribute is readOnly = true inside the @Transactional annotation.

2. Step 2: Check each option

   @Transactional(readOnly = true) uses the exact correct syntax. Others are either wrong attribute names or values.

3. Final Answer:

   @Transactional(readOnly = true) -> Option A

4. Quick Check:

   Correct syntax uses readOnly = true [OK]

Hint: Use readOnly = true exactly inside @Transactional [OK]

Common Mistakes:

• Using readOnly without = true
• Using readOnly = false by mistake
• Using non-existent attributes like enabled

3. Consider this Spring Boot method:

@Transactional(readOnly = true)
public List<User> getUsers() {
    userRepository.save(new User("John"));
    return userRepository.findAll();
}

What will happen when this method runs?

medium

A. An exception will be thrown because save is called in a read-only transaction

B. The save call will be ignored, but findAll will return existing users

C. The new user "John" will be saved and returned in the list

D. The method will run normally without any restrictions

Solution

1. Step 1: Understand read-only transaction restrictions

   Read-only transactions prevent data modifications like save or update operations.

2. Step 2: Analyze the method behavior

   Calling save inside a read-only transaction causes Spring or the database to throw an exception.

3. Final Answer:

   An exception will be thrown because save is called in a read-only transaction -> Option A

4. Quick Check:

   Save in read-only transaction = exception [OK]

Hint: Save inside read-only transaction causes error [OK]

Common Mistakes:

• Assuming save silently fails
• Thinking save works normally in read-only
• Ignoring transaction settings

4. You have this method:

@Transactional(readOnly = true)
public void updateUserName(Long id, String name) {
    User user = userRepository.findById(id).orElseThrow();
    user.setName(name);
}

Why might this method fail to update the user's name?

medium

A. Because the method is missing @Transactional annotation

B. Because findById does not return a user

C. Because setName is not a valid method

D. Because readOnly = true prevents any data changes inside the transaction

Solution

1. Step 1: Understand effect of readOnly = true on data changes

   Read-only transactions prevent changes from being saved to the database.

2. Step 2: Analyze the method's update attempt

   Even though the user object is modified, the transaction will not commit changes due to readOnly=true.

3. Final Answer:

   Because readOnly = true prevents any data changes inside the transaction -> Option D

4. Quick Check:

   readOnly = true blocks data updates [OK]

Hint: readOnly = true blocks saving changes [OK]

Common Mistakes:

• Assuming object changes auto-save without commit
• Thinking findById always fails
• Ignoring transaction annotation effects

5. You want to create a service method that fetches user data without risking accidental updates and improves performance. Which approach is best?

hard

A. Do not use any transaction annotation and perform all operations directly

B. Use @Transactional without readOnly and manually avoid updates

C. Annotate the method with @Transactional(readOnly = true) and avoid any save/update calls

D. Use @Transactional(readOnly = false) to allow updates if needed

Solution

1. Step 1: Identify the goal of safe read-only data fetching

   The goal is to read data safely without accidental changes and improve performance.

2. Step 2: Choose the best annotation and practice

   Using @Transactional(readOnly = true) explicitly marks the method as read-only, enabling optimizations and preventing writes.

3. Final Answer:

   Annotate the method with @Transactional(readOnly = true) and avoid any save/update calls -> Option C

4. Quick Check:

   Use readOnly = true for safe, optimized reads [OK]

Hint: Use readOnly = true to prevent accidental writes [OK]

Common Mistakes:

• Skipping readOnly and risking accidental writes
• Not using transactions at all
• Using readOnly = false when no updates needed