Re: Query JITing with LLVM ORC

Hi Thomas,

It JITs expressions but not whole queries.

Thanks for the clarification.

> Query execution at the
> tuple-flow level is still done using a C call stack the same shape as
> the query plan, but it *could* be transformed to a different control
> flow that could be run more efficiently and perhaps JITed.

I see, so there is room for extending the use of Orc JIT in PGSQL.

> CCing
> Andres who developed all this and had some ideas about that...
>

Thanks for CCing Andres, it will be great to hear from him.

> > I would love to know what motivated this feature and for what it is
> being currently used for,
>
> https://www.postgresql.org/docs/current/jit-reason.html

In that link I found the README under src/backend/jit, which was very
helpful.

> as it is not enabled by default.
>
> It's enabled by default in v12 and higher (if you built with
> --with-llvm, as packagers do), but not always used:
>
> https://www.postgresql.org/docs/current/jit-decision.html
>

Good to know. I compiled from the REL_14_5 tag and did a simple experiment
to contrast building with and w/o passing --with-llvm.
I ran the TPC-C benchmark with 1 warehouse, 10 terminals, 20min of ramp-up,
and 120 of measurement time.
The number of transactions per minute was about the same with & w/o JITing.
Is this expected? Should I use a different benchmark to observe a
performance difference?

Regards,

--
João Paulo L. de Carvalho
Ph.D Computer Science | IC-UNICAMP | Campinas , SP - Brazil
Postdoctoral Research Fellow | University of Alberta | Edmonton, AB - Canada
joao(dot)carvalho(at)ic(dot)unicamp(dot)br
joao(dot)carvalho(at)ualberta(dot)ca