Transactions

Group multiple statements into an atomic unit of work.

BEGIN/COMMIT/ROLLBACK

BEGIN;
  UPDATE accounts SET balance = balance - 100 WHERE id = 1;
  UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT; -- or ROLLBACK on error

Clients often expose transaction blocks/helpers; ensure errors trigger rollback.

ACID properties

• Atomicity: all or nothing
• Consistency: constraints hold before/after
• Isolation: concurrent transactions don’t interfere (see isolation levels)
• Durability: committed changes persist

Savepoints

BEGIN;
  SAVEPOINT sp1;
  UPDATE orders SET status = 'paid' WHERE id = 10;
  ROLLBACK TO SAVEPOINT sp1; -- undo partial work
COMMIT;

Retry patterns

Detect serialization conflicts and retry idempotent transactions.

Best practices

• Keep transactions short to reduce contention
• Touch rows in a consistent order to avoid deadlocks
• Enforce business invariants with constraints and unique indexes

Summary

• Use transactions for atomic changes; savepoints for partial rollback
• Design for retries under high concurrency