🔁BEGIN, COMMIT, ROLLBACK

Transactions are atomic story arcs

A transaction wraps a set of statements into one unit: succeed together or leave no trace (modulo isolation quirks readers observe). Autocommit turns every standalone statement into its own tiny arc, great for ad-hoc queries, risky for multi-step business invariants.

Explicit boundaries

Wrap transfers, inventory moves, and consent updates in BEGIN … COMMIT. Application frameworks often map one HTTP request to one transaction, know your default.

ROLLBACK is not shame

Validation failures, unique violations, and deadlock restarts should trigger rollback paths that your metrics count separately from user errors.

SQL

Happy path: explicit transaction

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

✓Illustrative result set

step
BEGIN
UPDATE 1 row
UPDATE 1 row
COMMIT

SQL

Abort path: rollback discards everything

BEGIN;
INSERT INTO transfers (from_id, to_id, amt) VALUES (1, 2, 500);
-- application detects insufficient funds
ROLLBACK;

✓Illustrative result set

state
no rows persisted

Long transactions holding locks

Starting a txn, calling slow external APIs, then updating rows pins locks and stalls everyone else, p99 latency explodes.

Pattern: shorten critical sections

Do network I/O first, then open the txn, mutate, commit quickly. For cross-service flows, use sagas with outbox patterns instead of one giant DB txn.

Savepoints

SAVEPOINT lets you partially roll back nested units inside one transaction, handy for complex stored procedures, but easy to misuse without clear naming and documentation.

Driver defaults

Autocommit wraps each standalone statement in its own transaction; DDL may issue implicit commits on many engines. Document session defaults next to deployment configs so on-call does not guess.

TL;DR

BEGIN (or START TRANSACTION) opens a unit of work; COMMIT makes durable what succeeded; ROLLBACK discards uncommitted changes. Savepoints add nested rollback points on some engines. Drivers often default to autocommit, explicit transactions are required for multi-statement invariants (transfers, inventory). Know DDL auto-commit rules on your database.