Brian Dunagan

September 15 2008
Atomic Transactions

I went to the gas station yesterday to fill up my car. It was the normal routine until I squeezed the pump handle and nothing happened. I tried it again, took the pump out, put it back in, squeezed. Nothing. After half a minute of this, the machine beeped and asked if I’d like my receipt. I said yes. It had charged my card $82, the amount the last person at the pump had paid.

I spent five minutes with the woman behind the gas station register, going back and forth about what exactly I did. Finally, she looked at my receipt and looked at her printout of credit card charges. No match. The gas pump machine had given me a receipt, but it hadn’t actually charged my card. I had no idea those two processes weren’t an atomic transaction.

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