The integration with their existing codebase might benefit from an explanation. In Go, calls to C libraries are done using a compiler feature called cgo, and there's a performance penalty that the cockroachdb team measured at 171ns per call, plus you sometimes have to copy additional data around for memory safety[0]. So far as I know, there's no way to avoid this penalty that doesn't involve building a tool that does the same thing as cgo.

In this case, given that they already have a database written in Go, writing the backing kv store library in Go has a clear performance benefit of 171ns every operation. This is above and beyond just familiarity and easy integration, although those are also important.

[0] https://www.cockroachlabs.com/blog/the-cost-and-complexity-o...