Re: JIT performance bug/regression & JIT EXPLAIN

On Fri, Nov 15, 2019 at 8:05 PM Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com> wrote:
> On Fri, Nov 15, 2019 at 5:49 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > Personally, I don't care very much about backward-compatibility, or
> > about how hard it is for tools to parse. I want it to be possible, but
> > if it takes a little extra effort, so be it.
>
> I think these are two separate issues. I agree on
> backward-compatibility (especially if we can embed a server version in
> structured EXPLAIN output to make it easier for tools to track format
> differences), but not caring how hard it is for tools to parse? What's
> the point of structured formats, then?

To make the data easy to parse. :-)

I mean, it's clear that, on the one hand, having a format like JSON
that, as has recently been pointed out elsewhere, is parsable by a
wide variety of tools, is advantageous. However, I don't think it
really matters whether the somebody's got to look at a tag called
Flump and match it up with the data in another tag called JIT-Flump,
or whether there's a Flump group that has RegularStuff and JIT tags
inside of it. There's just not much difference in the effort involved.
Being able to parse the JSON or XML using generic code is enough of a
win that the details shouldn't matter that much.

I think if you were going to complain about the limitations of our
current EXPLAIN output format, it'd make a lot more sense to focus on
the way we output expressions. If you want to mechanically parse one
of those expressions and figure out what it's doing - what functions
or operators are involved, and to what they are being applied - you
are probably out of luck altogether, and you are certainly not going
to have an easy time of it. I'm not saying we have to solve that
problem, but I believe it's a much bigger nuisance than the sort of
thing we are talking about here.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company