[dapperdrake]

Accurate a.k.a. "correct" implementation of ACID needs a single (central) source of truth and temporal serializability (or something close to that).

In practice this always "impacts" performance.

If I understand it correctly, then in physics this is called an event horizon.

[duped]

Not necessarily. Most race conditions violate the `A` in ACID, but the finicky thing about atomicity is that N > 1 sequential actions that in and of themselves are atomic violates atomicity. So any atomic store is possible to misuse if you can compose multiple atomic operations on it.

In addition ACID isn't always provided by the floor beneath your programs but by designing the programs on top to uphold it and/or not require it, allowing you to relax the constraints from your lower level interfaces for performance reasons.

[dapperdrake]

Firstly, atomicity and/or thread-safety not composing is where the Consistency and Isolation come in.

The "application layer" always has to enforce its own consistency guarantees. If the lower layers are total garbage, then the system is garbage. And the "speed" of the lower layers can be infinitely fast and it doesn’t matter, if the application has a latency floor. So optimize it all you want.