Re: JIT compiling with LLVM v11

On 2018-03-06 12:16:01 -0800, Andres Freund wrote:
> > I ran some performance assessments:
> >
> > merge base (0b1d1a038babff4aadf0862c28e7b667f1b12a30)
> >
> > make installcheck 3.14s user 3.34s system 17% cpu 37.954 total
> >
> > jit branch default settings
> >
> > make installcheck 3.17s user 3.30s system 13% cpu 46.596 total
> >
> > jit_above_cost=0
> >
> > make installcheck 3.30s user 3.53s system 5% cpu 1:59.89 total
> >
> > jit_optimize_above_cost=0 (and jit_above_cost=0)
> >
> > make installcheck 3.44s user 3.76s system 1% cpu 8:12.42 total
> >
> > jit_inline_above_cost=0 (and jit_above_cost=0)
> >
> > make installcheck 3.32s user 3.62s system 2% cpu 5:35.58 total
> >
> > One can see the CPU savings quite nicely.
>
> I'm not quite sure what you mean by that.
>
>
> > One obvious problem is that with the default settings, the test suite
> > run gets about 15% slower. (These figures are reproducible over several
> > runs.) Is there some debugging stuff turned on that would explain this?
> > Or would just loading the jit module in each session cause this?
>
> I suspect it's loading the module.

There's also another issue: For a lot queries in the tests the stats are
way way way off because the relevant tables have never been analyzed.
There's a few cases where costs are off by like 5-7 orders of
magnitude...

Greetings,

Andres Freund