On Mon, Jun 15, 2020 at 07:38:45PM -0700, Jeff Davis wrote:
On Mon, 2020-06-15 at 11:19 -0400, Robert Haas wrote:
On Mon, Jun 15, 2020 at 9:34 AM Tomas Vondra
<tomas.von...@2ndquadrant.com> wrote:
> But just reverting 4cad2534d will make this much worse, I think, as
> illustrated by the benchmarks I did in [1].
I share this concern, although I do not know what we should do about
it.
I attached an updated version of Melanie's patch, combined with the
changes to copy only the necessary attributes to a new slot before
spilling. There are a couple changes:
* I didn't see a reason to descend into a GroupingFunc node, so I
removed that.
* I used a flag in the context rather than two separate callbacks to
the expression walker.
This patch gives the space benefits that we see on master, without the
regression for small numbers of tuples. I saw a little bit of noise in
my test results, but I'm pretty sure it's a win all around. It could
use some review/cleanup though.
Looks reasonable. I can't redo my tests at the moment, the machine is
busy with something else. I'll give it a try over the weekend.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
