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Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

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Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#31

Post by PeterisP »

Aloisius wrote: post #9

Citation needed. I've never heard of financial systems being eventually consistent, certain not ATMs which need to know your exact balance and how much money you've taken out already today.

In most cases when processing a withdrawal, ATMs or POS terminals don't know your exact balance and how much money you've taken out already today. A withdrawal tends to involve a request for $X which gets a yes/no response from the bank or from the chip of the card if the terminal is not online connected - the bank or chipcard logic will check the balance and daily limits, not the ATM.

You can think of the (rare nowadays, but possible) offline, paper-based card transactions (physical imprint of the card number + signature) as a very strong example of eventual consistency - your card will be billed for that amount sometime later when the documents are processed and all the balances will be correct, but for many days the "online visible" card balance as known to the bank will be different from the "real" legal/accounting balance of that card.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#32

Post by threeseed »

Aloisius wrote: post #9

Citation needed. I've never heard of financial systems being eventually consistent, certain not ATMs which need to know your exact balance and how much money you've taken out already today.

I don't know if you've ever travelled but very often withdrawals from an ATM will be processed without the balance of the user being known at that time.

It's why your bank account can go into negative territory.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#33

Post by ExpiredLink »

The article is not entirely wrong but misleading. The two important aspects are authorization and limits.

Authorization: An ATM does not issue money without authorization which is done by some 'central authority', not the ATM.

Limits: In some corner cases you may be able to exceed your (daily, weekly, monthly) limits. But, as the article points out, this doesn't imply financial inconsistency.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#34

Post by brazzy »

jeremyjh wrote: post #7

>If an ATM is disconnected from the network and when the partition eventually heals, the ATM sends sends a list of operations to the bank and the end balance will still be correct. I don't think so. I support ATM client software for a large bank in the US and we certainly don't do this. This may be true for "remote" ATMs that are installed in convenience stores on POTS. I can't say I've ever actually heard of it thou…

> the main problem with this idea is that cards cannot be authenticated without network access, and just spewing out money to every piece of plastic calling itself a card when your network connection has been dropped isn't really a recipe for success. Fraud is a real problem.

I believe some of the first ATMs actually worked offline (the PIN was encoded on the magentic stripe), but networked models came out a few years later. Of course, this was in the late 1960s, when card readers (and the expertise to use them) were far harder to obtain.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#35

Post by lrobb »

jeremyjh wrote: post #7

>If an ATM is disconnected from the network and when the partition eventually heals, the ATM sends sends a list of operations to the bank and the end balance will still be correct. I don't think so. I support ATM client software for a large bank in the US and we certainly don't do this. This may be true for "remote" ATMs that are installed in convenience stores on POTS. I can't say I've ever actually heard of it thou…

It certainly appeared that way to me as well. Although I don't really use ATMs much today, it used to be a fairly regular occurrence to arrive at an ATM then have to find the "next closest ATM" due to the machine having connectivity problems.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#36

Post by diroussel »

timv wrote: post #29
Maxious wrote: post #15

Earlier quoted context omitted.

> just spewing out money to every piece of plastic calling itself a card when your network connection has been dropped isn't really a recipe for success. Well they do this in Australia... http://www.news.com.au/money/banking/computer-glitch-hits-cb... > "People were running past me screaming 'Free money! Free money!'," Punchbowl Pharmacy manager Feriale Zakhia said of the people using a nearby ATM. > "Everyone was so…

Leaving aside the fact that I wouldn't trust a newspaper to for the technical details of something like this, nothing in the article contradicts what jeremyjh said. In that case, the ATM was disconnected from the accounting system and allowed withdrawals up to a set limit ($2000), but it (probably, the article is unclear) was still connected to the authorization system. It (probably) still checked your PIN, and check…

Which in turn agrees with the point of the original article. ATMS use BASE not ACID as it's more profitable to be available.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#38

Post by jeremyjh »

SoftwareMaven wrote: post #13
jeremyjh wrote: post #7

>If an ATM is disconnected from the network and when the partition eventually heals, the ATM sends sends a list of operations to the bank and the end balance will still be correct. I don't think so. I support ATM client software for a large bank in the US and we certainly don't do this. This may be true for "remote" ATMs that are installed in convenience stores on POTS. I can't say I've ever actually heard of it thou…

Reading this, it doesn't sound like you said anything different. Sure, it isn't the ATM itself that makes the decision, but the authorization system can still step in and allow a transaction that is not committed to the actual account's log. I'm sure that, under the hood, there are a lot of ACIDic transactions going on, but, stepping back, it still looks pretty BASEic. When I hit "withdraw $200", there is no guarante…

Yes and I acknowledged this at the end of my comment I think.

I don't really think it is useful to try and use the terms ACID/BASE to refer to the aggreggate process behavior of an entire industry's technology. Not that it is wrong, it just really doesn't mean anything at that point. Most data interchange that takes place between thousands of different parties is going to have similar characteristics. Maybe a market/exchange is a good counter-example but I can't think of many others.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#39

Post by trotsky »

This seems like a pretty bad strategy to sell nosql etc. What are we supposed to believe, that every ATM downloads account numbers, pin hashes and balances for every account in their network?

Banks have chosen consistency over availability regularly as they've been able to rebuild their systems over the decades. 40 years ago, if you had a credit card the place just took it, copied it down and trusted you and the bank were good for it. Try to get anyone to take your credit card if the network is down now.

IMO banking culture and standards probably were direct motivators of many of the ways traditional systems were designed. They were some of the earliest adopters of IT. It may not be accurate to say banks or ACID. It may be more accurate to say ACID is banking.

Re: Eric Brewer on Why Banks are BASE, Not ACID – Availability Is Revenue

#40

Post by GFischer »

diroussel wrote: post #36
timv wrote: post #29

Earlier quoted context omitted.

Leaving aside the fact that I wouldn't trust a newspaper to for the technical details of something like this, nothing in the article contradicts what jeremyjh said. In that case, the ATM was disconnected from the accounting system and allowed withdrawals up to a set limit ($2000), but it (probably, the article is unclear) was still connected to the authorization system. It (probably) still checked your PIN, and check…

Which in turn agrees with the point of the original article. ATMS use BASE not ACID as it's more profitable to be available.

Those humungous overdraft fees will definitely be profitable :)

BTW I've been scammed out of money by ATMs before - money was withdrawn from my account but some system jammed and I didn't get the money - and the bank was awfully uncooperative.

So far I've had more luck with the "money under the mattress" method than with banks - and I wasn't trapped in the "Corralito" or other bank-aided money-stealing schemes

http://en.wikipedia.org/wiki/Corralito

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