3 ms·
A lot of people don't realize that our entire financial system is eventually consistent. They think that when they go to an ATM and withdraw money, it's instan
by jedberg 1y ago
A lot of people don't realize that our entire financial system is eventually consistent. They think that when they go to an ATM and withdraw money, it's instantly gone from their account.
The reality is that in most cases the convergence is so quick it looks like it's instantly gone, but it's not. For example, if the ATM is unable to get your current balance, it will still complete the transaction.
That's why your card has a daily limit -- that's basically the risk tolerance of the bank on how much they are willing to lose if the transactions don't get converge quickly enough.
- chihuahua 1y agoIn a few places, you can see traces of this aspect of the system. For example, some gas pumps put a $150 "hold" on your card, and on your bank's web site, you may be able to see "pending" transactions that are in some not-quite-final state.
- kassner 1y agoThat’s a different thing: pre-authorization. It’s used for when you want to authorize some purchase before delivering the goods (that you later confirm once it’s delivered). The pre-auth is still done online for amounts above the card-offline limit. The nicer feature of preauth is that you can confirm a lower amount. So in the case of a gas pump, they first have to make sure you have the money, without knowing how much, because you haven’t pumped it yet. Once you finish, then they know the amount, and confirm the transaction at a lower amount.