[jandrewrogers]

Hilbert curve is only useful if the sole goal is sequential storage of point data. Z-curves are superior in almost every other case in real systems due to their unique and efficient computational properties, which many computer scientists are only vaguely aware of.

And since modern spatial database architectures don't sequentialize storage along the curve (because it doesn't make sense as a matter of engineering), the sole selling point of Hilbert curves is moot. You shouldn't design most systems in a way that could exploit the benefits of a Hilbert curve.

[DocSavage]

Could you elaborate on your comment about modern spatial databases not sequentializing storage along the curve? I would imagine parallel access across the curve, but wouldn't you want some reasonable sequential access at each cluster node to maximize IO speeds?

I've read your blog entries on SpaceCurve (http://www.jandrewrogers.com/2015/10/08/spacecurve/), found them very interesting but also just whetting the appetite. Are there no public reviews or papers covering discrete topology/sharding?

[jandrewrogers]

There are two design factors that most people overlook:

Most people know you can use Z/C-curve encodings to dynamically content address point data. There is a (very useful) generalization to hyper-rectangle types, perfect for content-addressing non-point geometries etc, but those types can't be meaningfully sequentialized at all in big systems. Most non-trivial spatial analytics involve non-point geometries, so being able to sequentialize points has limited utility.

Second, the computational cost of sorting along the curve, assuming you are using only points, is prohibitively high for negligible benefit. Modern storage engines use small shards, which are adaptively re-sharded as needed, and medium-sized pages. For insert, the content-addressing mechanic gets you to a single page; it would be significantly more expensive if you were sorting along the curve. For query, the typical selectivity on a shard is so high due to small adaptive shards, that you are better off treating it as an unsorted vector anyway. In short, much slower inserts and few (if any) query benefits.

As an optimization, it tends to only be applicable in cases where the architecture is significantly suboptimal anyway e.g. the use of gigantic shards. You'd get more benefit by fixing the architecture than trying to optimize poor architecture if at all possible.