Agree, Rust seems like a good choice but I'm curious why they needed to replace Go. GC pause time is mostly due to the amount of pointer-containing heap memory.

Agree, Rust seems like a good choice but I'm curious why they needed to replace Go. GC pause time is mostly due to the amount of pointer-containing heap memory. Moving the the cache storage to slabs of pointer-free "dumb" slices should pretty much avoid the problem so long as you force GC frequently (large heap will confuse the heuristic). Shard the slabs across a handful of goroutines, one channel each to handle locking, and that should perform fine compared to an equivalently complex Rust implementation.