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The propagation levels in transaction management determine how a transaction behaves when calling methods that can also be transactional. This is important to understand whether a method will use an existing transaction, create a new one, or operate without a transaction.

The main propagation levels in Spring (Java):

• REQUIRED (default): if there is an existing transaction, the method joins it; otherwise, a new one is created.
• REQUIRES_NEW: always creates a new transaction, suspending the current one (if any).
• SUPPORTS: if there is a transaction, the method works within it; otherwise, without a transaction.
• NOT_SUPPORTED: the method always executes without a transaction, suspending the current one.
• MANDATORY: the method must be executed within an existing transaction; otherwise, an exception is thrown.
• NEVER: the method must not be executed within a transaction; otherwise, an exception is thrown.
• NESTED: if there is a transaction, a nested (savepoint) transaction is created; otherwise, a new one is.

Example:

@Transactional(propagation = Propagation.REQUIRES_NEW)
public void saveData() {
    // this method is always in a new transaction
}