I'd ignored this, trying to have a nice holiday with my family (without having to contend with wrongness on the internet :), but would like to introduce some facts. Datomic is not an append-only b-tree, and never has been.
There's a presumption in the article that "immutable" implies "append-only b-tree", specifically, an argument against append-only b-trees is used to disparage immutability. That's pretty naive. One only need to look at e.g. the BigTable paper for an example of how non-append immutability can be used in a DB. Such architectures are now pervasive. Datomic works similarly.
One can't make a technical argument against keeping information. It's obviously desirable (git) and often legally necessary. Our customers want and need it. Yeah, it's also hard, but update-in-place systems (including MVCC ones) that discard information can't possibly be considered to have "solved" the same problem.
Prefixing a polemic with "apparently" doesn't get one off the hook for spreading a bunch of misinformation.
There's a presumption in the article that "immutable" implies "append-only b-tree", specifically, an argument against append-only b-trees is used to disparage immutability. That's pretty naive. One only need to look at e.g. the BigTable paper for an example of how non-append immutability can be used in a DB. Such architectures are now pervasive. Datomic works similarly.
One can't make a technical argument against keeping information. It's obviously desirable (git) and often legally necessary. Our customers want and need it. Yeah, it's also hard, but update-in-place systems (including MVCC ones) that discard information can't possibly be considered to have "solved" the same problem.
Prefixing a polemic with "apparently" doesn't get one off the hook for spreading a bunch of misinformation.