[richardw]

Banking, 7 ish years. Worked well for us in general. When I start needing increased confidence and truth the effort level goes way up but can be done. Definitely still worth it, has given us some solid benefits.

When I say increased, I mean we want the best answer but there are some answers the bank can’t know. If someone has transferred money into your account from another bank but we don’t know that yet, optimising for absolute correctness is pointless because the vast majority of wrong answers are baked in to the process. We can send you a message and you might read it a day later. Unless we delete the message from your phone, we can’t guarantee the message you read is fully consistent with our internal state.

Frankly our system is much better than the batch driven junk that is out of sync a second after it has executed. “Hey you have a reward.” “No I used it 2 hours ago you clowns.”

Note this isn’t cope. In some cases we started fully sync but relaxed it where there are tradeoffs that gave us better outcomes and we weren’t giving anything material up.

[lanstin]

Or worse “hey you have a reward” but it doesn’t show up in the UI for three minutes. Twitter used to do this to me all the time.

[richardw]

Eventually consistent means just that, I guess. But I’m sure their reasoning was a lot more sophisticated or impacted by scale than most. Cool problem.