Re: jit and explain nontext

On Thu, 15 Oct 2020 at 14:15, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > Just for some reference. Some wisdom was shared in [1], which made a
> > lot of sense to me.
> > If we apply that, then we just need to decide if displaying any jit
> > related fields without any jitted expressions is relevant.
>
> Hmm, I dunno if my opinion counts as "wisdom", but what I was arguing for
> there was that we should print stuff if it's potentially invoked by a
> run-time decision, but not if it was excluded at plan time. I'm not
> totally clear on whether jitting decisions are fixed by the plan tree
> (including its cost values) or if the executor can make different
> decisions in different executions of the identical plan tree.
> If the latter, then I agree with Justin that this is a bug.

As far as I know, the only exception where the executor overwrites the
planner's decision is in nodeValuesscan.c where it turns jit off
because each VALUES will get evaluated just once, which would be a
waste of effort to JIT.

Apart from that the choice is baked in by the planner and set in
PlannedStmt.jitfFlags.

David