Why should you care?

Payment gateway timeout means order must not persist — ROLLBACK clears pending inserts and restores locked stock.

See it live — copy this example

Run in MySQL Workbench or the mysql CLI.

START TRANSACTION;
UPDATE products SET stock_qty = stock_qty - 1 WHERE product_id = 5;
INSERT INTO orders (customer_id, order_ref, total_inr) VALUES (1, 'DF-FAIL', 999.00);
-- Gateway declined
ROLLBACK;
SELECT stock_qty FROM products WHERE product_id = 5;

What happened?

• After ROLLBACK, stock update vanishes as if txn never ran.
• orders row not inserted.
• SELECT shows original stock_qty — critical for failed checkout paths.

Practice next

1. Note stock before txn.
2. Run update + insert then ROLLBACK.
3. Confirm stock and orders unchanged.
4. Use ROLLBACK in stored procedure handler on SQLEXCEPTION.
5. Pair try/catch in app with conn.rollback().

Remember

ROLLBACK = abort current transaction. Uncommitted changes disappear. Always rollback on unhandled app errors.

DataFlow failed UPI

Node service catches gateway 402 and issues ROLLBACK on MySQL connection.

Outcome: Inventory and order tables stay consistent with payment state.