
Ask HN: Do banks use OLTP or event sourcing to process money transactions? - itaifrenkel
We were having a &quot;lunch&quot; discussion if banks still take every transaction and write it to an OLTP database, or do they use event sourcing. The fact that ATMs need to provide money when disconnected, or the fact that transaction takes 24h to approve suggest it might not be a direct OLTP transaction. Anyone implemented a bank system care to shed some light on the matter ?
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mattkrea
> The fact that ATMs need to provide money when disconnected

Is this a fact though? We provide ATM rentals/leases for our customers (though
few ask for it these days) and I'm pretty sure they do not function if they
are disconnected.

As far as I am aware a failure to connect to the issuing bank for a card will
cause your card to be declined so that would lead me to believe their
mainframes (and yes they are actually IBM mainframes in the cases I've
experienced) must be online and connected.

Regarding the 24-48hr approval process.. that is more because of batches. And
you're dealing with a responsible merchant (or host-capture environment) if
you get those timeframes.

A merchant can wait for days to batch their credit cards in which case you're
waiting as well.

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itaifrenkel
Woudn't an ATM that is not connected to the mainframe let you withdraw even a
small amount of money?

~~~
mattkrea
Not that I'm aware of. There is no way to even verify the card.

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ereli1
most banks don't talk about this stuff, either since their tech is outdated or
because they don't think customers are interested in improvements in this
field. the new banks in the UK
[https://monzo.com/blog/](https://monzo.com/blog/)
[https://www.atombank.co.uk/blog](https://www.atombank.co.uk/blog)
[https://www.starlingbank.com/blog/](https://www.starlingbank.com/blog/) don't
blog about their stack as much as you'd hope - but they do everything online.

