Read-only transactions in Spring Boot - Step-by-Step Execution

Concept Flow - Read-only transactions

Start method call

↓

Begin transaction

↓

Set transaction read-only = true

↓

Execute database operations

↓

Check for write attempts

↓

Commit transaction

↓

End method

This flow shows how a read-only transaction starts, runs database reads, prevents writes, and commits or rolls back accordingly.

Execution Sample

Spring Boot

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

This method runs inside a read-only transaction to fetch users without allowing data changes.

Execution Table

Step	Action	Transaction State	Write Attempt	Result
1	Method getUsers() called	No transaction	No	Start transaction
2	Begin transaction	Active, read-only=true	No	Transaction started as read-only
3	Execute userRepository.findAll()	Active, read-only=true	No	Data read from DB
4	Attempt to write data (if any)	Active, read-only=true	Yes	Error or rollback triggered
5	Commit transaction	No transaction	No	Transaction committed
6	Method ends	No transaction	No	Transaction closed

💡 Transaction ends after commit or rollback; no writes allowed in read-only mode

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
transactionState	No transaction	Active, read-only=true	Active, read-only=true	No transaction	No transaction
writeAttempt	No	No	No	No	No or Error if attempted

Key Moments - 3 Insights

Why does the transaction prevent data writes even if the code tries to save or update?

Because the transaction is marked read-only (see execution_table step 4), the database or framework blocks write operations to protect data integrity.

What happens if a write is attempted inside a read-only transaction?

An error is thrown or the transaction rolls back immediately, as shown in execution_table step 4, preventing any data changes.

Does a read-only transaction still open a database transaction?

Yes, it opens a transaction but with a read-only flag (execution_table step 2), optimizing for reads and disallowing writes.

Visual Quiz - 3 Questions

Look at the execution_table, what is the transaction state after step 3?

A Active, read-only=true

B No transaction

C Active, read-write

D Rolled back

💡 Hint

Check the 'Transaction State' column at step 3 in the execution_table.

At which step does the transaction commit if no writes occur?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look for the 'Commit transaction' action in the execution_table.

If a write attempt happens at step 4, what is the expected result?

A Transaction commits successfully

B Error or rollback triggered

C Transaction ignores the write

D Transaction converts to read-write

💡 Hint

See the 'Result' column at step 4 in the execution_table.

Concept Snapshot

@Transactional(readOnly = true) marks a method's transaction as read-only.
This optimizes for reading data and prevents any writes.
If a write is attempted, an error or rollback occurs.
The transaction still opens but disallows data changes.
Use it for methods that only fetch data to improve performance and safety.

Full Transcript

In Spring Boot, marking a method with @Transactional(readOnly = true) starts a transaction flagged as read-only. This means the method can read data but cannot write or change it. When the method runs, the transaction begins with read-only set to true. If the code tries to write data, the transaction will throw an error or roll back to prevent changes. If no writes happen, the transaction commits normally. This helps optimize database access and protects data integrity by ensuring no accidental writes occur during read-only operations.