Re: JIT compiling with LLVM v11

On 2018-03-11 13:19:57 -0400, Peter Eisentraut wrote:
> On 3/9/18 15:56, Andres Freund wrote:
> > I think that's largely that unnecessary trivial queries get JITed and
> > optimized, because the stats are entirely completely off.
>
> Right. I instrumented this a bit, and there are indeed two handfuls of
> queries that exceed the default JIT thresholds, as well as a few that
> trigger JIT because they disable some enable_* planner setting, as
> previously discussed.
>
> Should we throw in some ANALYZEs to avoid this?

Hm, I'd actually lean to just leave it as is for now. JITing halfway
random queries isn't actually that bad... If we get fed up with the
additional time after a while, we can do something then?

> It's perhaps a bit confusing that some of the jit_* settings take effect
> at plan time and some at execution time. At the moment, this mainly
> affects me reading the code ;-), but it would also have some effect on
> prepared statements and such.

Not quite sure what you mean?

> Also, jit_tuple_deforming is apparently used only when jit_expressions
> is on.

Right. I've not found a good place to hook into that has enough context
to do JITed deforming otherwise. I'm inclined to just relegate
jit_tuple_deforming to debugging status (i.e. exclude from show all,
docs etc) for now.

> So, we should work toward more clarity on all these different settings,
> what they are useful for, when to set them, how they interact.

Yep.

Greetings,

Andres Freund