Propagation answers one question: when an annotated method is called, what does it do about an already-running transaction on the current thread — join it, suspend it and start a new one, or insist on a particular state? There are seven values; REQUIRED is the default and covers most code.
The seven values
REQUIRED (default) — join the existing transaction if there is one, otherwise create a new one. The common case: nested service calls share one transaction, so a failure anywhere rolls the whole thing back.
REQUIRES_NEW — always suspend any existing transaction and start a brand-new, independent one. It commits or rolls back on its own; the outer transaction resumes afterward. Use it for work that must persist regardless of the caller's fate — an audit log or outbox row you want kept even if the business transaction rolls back.
@Transactional(propagation = Propagation.REQUIRES_NEW)
public void writeAuditEntry(AuditEvent e) {
auditRepo.save(e); // commits independently of the calling transaction
}NESTED — runs in a savepoint inside the current transaction (JDBC only; needs savepoint support). The inner work can roll back to the savepoint without killing the outer transaction, but it commits only when the outer one commits. Different from REQUIRES_NEW, which is a fully separate transaction.
SUPPORTS — run inside a transaction if one exists, otherwise run non-transactionally. For read methods that don't strictly need a transaction but should join one if present.
NOT_SUPPORTED — suspend any existing transaction and run non-transactionally. Useful for long, non-transactional work you don't want holding a connection.
MANDATORY — there must already be a transaction, otherwise throw IllegalTransactionStateException. Enforces "this method may only be called inside an existing transaction."
NEVER — there must be no transaction; throw if one exists.