alt Hacker NewsNot sure where the idea comes from that Cranelift is much faster than LLVM -O0, at least in our experiments in 2024 it wasn't, see [1] Fig. 6.
Template-based code generators suffer from bad code quality due to missing register allocation.
Our TPDE-based compilers compile a bit slower than template-based code generation but the generated code is much smaller and faster ([2] Fig. 2). Also for database workloads ([2] Fig. 6).
All that said, Postgres' main limitation is that it (IIRC) only compiles single expressions from operators, not pipelines. This fundamentally limits the achievable performance improvement compared to databases that perform more extensive query compilation.
[1]: https://aengelke.net/pubs/2403-cgo.pdf [2]: https://aengelke.net/pubs/2602-cgo1.pdf
PS: sorry for the promotion of my own research here, just couldn't resist.
Always good to have proper researchers in the thread.
> Not sure where the idea comes from that Cranelift is much faster than LLVM -O0
Cranelift describes itself as a fast, secure, relatively simple and innovative compiler backend. [0] Interesting that LLVM can compete there, with its optimisations dialed down.
> Postgres' main limitation is that it (IIRC) only compiles single expressions from operators, not pipelines. This fundamentally limits the achievable performance improvement compared to databases that perform more extensive query compilation.
That sounds pretty limiting. That's separate from query optimisation though, right? The query optimiser is presumably able to reason 'broadly' and not just at the level of individual expressions? High-level query-plan optimisation must be much more consequential than effective use of JIT compilation.
[0] https://cranelift.dev/