Like quite a few people here (I’m guessing), I’ve been nodding along and stroking my beard (optional) in the great MD vs AD debates (links below), kind of getting it - but mostly not, at least in terms of the big picture.
I think a step back would be useful: what’s the point of immutability?
Intuitively, the idea of never deleting anything puts one in mind of those documentaries where we see into the homes of people who just can’t throw anything away. “Why are they living in squalour amongst those broken umbrellas, yellowed newspapers and dog poo,” we ask? The obvious answer is because they’re slightly nuts with an impractical attachment to the past.
But the horders will have their own internal logic which they will find it hard to explain to others, but they might point to some examples. BBC archivists thought it made sense to tape over Beatles footage and Dr Who to make space for Terry and June (apologies to non-Brits and young people).
Computer scientists attached to immutability will similarly struggle to explain their apparent data hording to others. Why keep hold of rubbish that you could chuck away and make space for useful stuff? It’s counterintuitive to say the least. But most peole aren’t great at exponentials and computing power and storage vs cost have been increasing exponentially, and probably will for a while. If our houses increased exponentially in size with time it would make perfect sense to keep the broken umbrellas and old papers because there’s a chance they’d be useful at some time in the far distant future, and there’d always be space for them. We’d be considered sensible, not nuts, for keeping them.
See the brilliantly titled Immutability Changes Everything by Pat Helland
But what about the dog poo? Surely even accounting for exponential jiggery pokery it doesn’'t make sense to store that? It it might be vaguely useful as fertiliser short-term but it will soon decay and rot into nothing, becoming worthless.
Getting to the point, I’d like to see some explanation about how SAFE might work in IoT situations where sensors are churning out readings every 1/100 seconds. This sort of data will increase massively, but it’s dog poo: there’s surely no point in keeping it in its raw form?
Will sensor data be dealt with in a client to client way, being aggregated by some app before being stored forever or will that be outside of the scope of SAFE? If so where does that app live? I don’t think SAFE should be limited to static archival storage as that’s already relatively cheap and simple and there will be no market for it. So how will SAFE deal with streaming data?
I think how SAFE fits into the paradigm shift of exponential expansion of compute/storage needs to be explained more clearly and separate from the technical arguments about data types and so on, and there are further discussions to be had about what immutability means for the more abstract notions of freedom and access to information, but that’s maybe for a different thread.