Date: Thu, 20 Sep 2018 09:07:21 -0400
From: Stephen Frost <sfrost@snowman.net>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Amit Khandekar <amitdkhan.pg@gmail.com>,
	Andreas Joseph Krogh <andreas@visena.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	"Jonathan S. Katz" <jkatz@postgresql.org>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Query is over 2x slower with jit=on
Message-ID: <20180920130721.GM4184@tamriel.snowman.net>
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Greetings,

* Andres Freund (andres@anarazel.de) wrote:
> On 2018-09-19 23:26:52 -0400, Tom Lane wrote:
> > Andres Freund <andres@anarazel.de> writes:
> > > JIT:
> > >   Functions: 2
> > >   Generation Time: 0.680 ms
> > >   Inlining: true
> > >   Inlining Time: 7.591 ms
> > >   Optimization: true
> > >   Optimization Time: 20.522 ms
> > >   Emission Time: 14.607 ms
[...]
> > > How about making that:
> > > JIT:
> > >   Functions: 2
>=20
> FWIW, not that I want to do that now, but at some point it might make
> sense to sub-divide this into things like number of "expressions",
> "tuple deforming", "plans", ...  Just mentioning that if somebody wants
> to comment on reformatting this as well, if we're tinkering anyway.

I'd actually think we'd maybe want some kind of 'verbose' mode which
shows exactly what got JIT'd and what didn't- one of the questions that
I think people will be asking is "why didn't X get JIT'd?" and I don't
think that's very easy to figure out currently.

> > >   Options: Inlining, Optimization
> > >   Times (Total, Generation, Inlining, Optimization, Emission): 43.4 m=
s, 0.680 ms, 7.591 ms, 20.522 ms, 14.607 ms
> >=20
> > > or something similar?
> >=20
> > That's going in the right direction.  Personally I'd make the last line
> > more like
> >=20
> >     Times: generation 0.680 ms, inlining 7.591 ms, optimization 20.522 =
ms, emission 14.607 ms, total 43.4 ms
>=20
> Yea, that's probably easier to read.

I tend to agree that it's easier to read but I'm not sure we need to
quite go that far in reducing the number of rows.

> > (total at the end seems more natural to me, YMMV).

I agree with this..

> I kind of think doing it first is best, because that's usually the first
> thing one wants to know.

and this, so what about:

Times:
  generation 0.680 ms, inlining 7.591 ms, optimization 20.522 ms, emission =
14.607 ms
  Total: 43.4 ms

Gets the total out there quick on the left where you're scanning down
while keeping the detailed info above for reviewing after.

> > Also, the "options" format you suggest here seems a bit too biased
> > towards binary on/off options --- what happens when there's a
> > three-way option?  So maybe that line should be like
> >=20
> >     Options: inlining on, optimization on
> >=20
> > though I'm less sure about that part.
>=20
> I'm pretty certain you're right :).  There's already arguments around
> making optimization more gradual (akin to O1,2,3).

That certainly sounds like it'd be very neat to have though I wonder how
well we'll be able to automatically plan out which optimization level to
use when..

Thanks!

Stephen

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