Database Tutorial #6: PostgreSQL Transactions and Concurrency
Two users buy the last item in stock at the same time. Your app charges a card, then the payment service fails. A report runs while someone is editing data. These are concurrency problems. Transactions solve them. What is a Transaction? A transaction is a group of SQL statements that execute as one unit. Either all succeed or none apply. BEGIN; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; COMMIT; If anything fails between BEGIN and COMMIT, call ROLLBACK to undo everything: ...