Application Integration & Schema Evolution

Connections, Sessions, and Protocols

A connection is a transport carrying a database protocol; a session is server-side identity and mutable context; a transaction is a bounded atomic history within that session. Correct clients establish, use, reset, and discard each layer deliberately.

Transport, protocol, session, and transaction are distinct.
Authentication is not authorization.
Session state survives transaction boundaries.
Protocol phases constrain legal recovery.
Cancellation and connection loss have different meanings.
Reset is a correctness operation.

Layered lifecycle and failure boundary

State ownership and cleanup
Layer	Representative state	End/reset signal
Transport	socket, TLS keys, liveness	close/discard
Protocol	message sequence, portals/cursors	responses drained; driver ready
Session	principal, role, settings, temporary/prepared objects	vendor/driver reset contract
Transaction	snapshot, locks, writes, failed flag	COMMIT or ROLLBACK acknowledged

A defensive checkout contract

acquire(deadline)
  verify connection is live and driver says IDLE
  establish required role, schema, time zone, and statement timeout
  execute work; consume or close every result
finally
  if transaction active/failed: ROLLBACK and verify acknowledgement
  restore session contract; otherwise discard
  return only a known-clean connection