Software Development

Your ATM doesn’t use transactions

I just got a series of SMSes from my back, saying that someone just made several withdrawals from my account. As I am currently sitting and watching TV, I was a bit concerned.

It appears that my wife withdrew some money, but there was an issue with one ATM machine, so she used another one.

The problem, I got 3 SMS messages, saying that the follow activities happened on my account:

  • ATM withdrawal for 2,000 NIS
  • ATM withdrawal for 2,000 NIS
  • ATM withdrawal for 2,900 NIS

Checking with my wife, she had actually withdrawn only 2,900.

I was a bit concerned, so I logged into the bank and got this:


In English, this is:

DateDescriptionAuth CodeDebitCredit
10 AprATM withdrawal000035812,000
10 AprATM withdrawal000035812,000
10 AprATM withdrawal000035812,900

This is actually interesting, because the way my wife described it, she wen to the ATM, punch the right codes, and went through the motions of everything. Then, just before it was about to give her the money, it failed.

What is really interesting? From my point of view, is that I can actually see this in my bank account. We didn’t have a transaction rollback because of failure to dispense the money. That isn’t how ATM works. We actually had a compensating action (that occurred as separate transaction) to show that the ATM refunded the money it wasn’t able to give.

So next time someone tries to quote you “banks use transactions”, you can tell them that the bank definition of what a transaction is would make any decent DTC cry with shame.

Reference: Your ATM doesn’t use transactions from our NCG partner Oren Eini at the Ayende @ Rahien blog.

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