It appears that all these extra functions are written in Rust, but the core Timescale product is written in C. Why did you do it that way? Would you do it differently if you were starting from scratch today?
This is all true! We have a bit more info on that choice in this post [1].
But in general the Toolkit extension [2] is meant to have a bit of a lighter touch than the core TimescaleDB extension [3], it's meant for moving faster and working almost entirely with the custom functions/types/operators type approach rather than the core extension which is integrated much more deeply into the planner & executor and deals with a number of other hooks. It would be possible to do that in Rust, but because it's so deeply integrated with the main Postgres codebase there would just be a lot of translation going on and you'd get a lot less of the benefits of working in Rust. So C is more natural for much of the core DB extension.
PGX [4] is also a huge help for writing this sort of extension. The point of Toolkit is really to move much faster, try lots of things, mostly using the more SQL facing API (CREATE FUNCTION, CREATE AGGREGATE and the like). And PGX helps manage all of that really nicely. The rest of Rust being available is also great and we like working in the language, but without PGX it'd be a lot harder and we couldn't move nearly as fast.
