alt Hacker News> It's very difficult to do low-latency queries if you cannot cache the compiled code
This is not too difficult, it just requires a different execution style. Salesforce's Hyper for example very heavily relies on JIT compilation, as does Umbra [1], which some people regard as one of the fastest databases right now. Umbra doesn't cache any IR or compiled code and still has an extremely low start-up latency; an interpreter exists but is practically never used.
Postgres is very robust and very powerful, but simply not designed for fast execution of queries.
Disclosure: I work in the group that develops Umbra.
If I recall research papers regarding Umbra it's also using AsmJit as a JIT backend, which means that theoretically the compilation times would be comparable if you only consider code emitting overhead.
The problem will always be queries where the compilation is orders of magnitude more expensive than the query itself. I can imagine indexed lookup of 1 or few entries, etc... Accessing indexed entries like these are very well optimized by SQL query engines and possibly make no sense JIT optimizing.