I did this. I previously worked at a search engine which did its index building and querying in C, with its higher-level stuff (web-apps, scheduling, tooling,

I did this. I previously worked at a search engine which did its index building and querying in C, with its higher-level stuff (web-apps, scheduling, tooling, etc.) in Java. Later when I built my own version, I started with C for the low-level and Haskell for the high-level. I made a few iterations in C, but eventually rewrote it in Rust, and I was pretty happy with that choice. I was more familiar with C, and it was a really good fit for what I was writing. Terms and Documents just become termIds and docIds (numbers) sitting in indexes (arrays). Memory-mapping is a really comfortable way to do things: files are just arrays; let the OS sort out when to page things in and out of disk. But where C fell down for me was in the changing the code. The meaning of the data&code were lost in nested for-loops and void-function-pointers, etc. Rust gave me a better shot at both writing and rewriting the code. Java for the low-level was a non-starter for me for a few reasons, but the biggest two were startup time and difficulty of the mmap api (31-bits of address-space for a file? c'mon!).