Flush, Persist & Cache

`evict()` and `detach()` remove one entity from tracking; `clear()` removes all; none touch the database row.

`save()` buffers the SQL until flush time; `saveAndFlush()` forces the SQL out immediately -- both are still inside the transaction and can roll back.

Flush sends SQL to the database now but keeps the transaction open; commit finalizes the transaction and makes changes permanent; flushed-but-uncommitted changes can be rolled back.

`save()` makes the entity managed and queues the INSERT; the SQL is deferred to flush or commit so Hibernate can batch and order statements.

AUTO flushes before affected queries and at commit; COMMIT flushes only at commit; MANUAL flushes only on explicit `flush()` calls.