Re: Hybrid Hash/Nested Loop joins and caching results from subplans

Hi,

On 2020-07-09 10:25:14 +1200, David Rowley wrote:
> On Thu, 9 Jul 2020 at 04:53, Andres Freund <andres@anarazel.de> wrote:
> >
> > On 2020-05-20 23:44:27 +1200, David Rowley wrote:
> > > I've attached a patch which implements this.  The new node type is
> > > called "Result Cache".  I'm not particularly wedded to keeping that
> > > name, but if I change it, I only want to do it once. I've got a few
> > > other names I mind, but I don't feel strongly or confident enough in
> > > them to go and do the renaming.
> >
> > I'm not convinced it's a good idea to introduce a separate executor node
> > for this. There's a fair bit of overhead in them, and they will only be
> > below certain types of nodes afaict. It seems like it'd be better to
> > pull the required calls into the nodes that do parametrized scans of
> > subsidiary nodes. Have you considered that?
> 
> I see 41 different node types mentioned in ExecReScan().  I don't
> really think it would be reasonable to change all those.

But that's because we dispatch ExecReScan mechanically down to every
single executor node. That doesn't determine how many nodes would need
to modify to include explicit caching? What am I missing?

Wouldn't we need roughly just nodeNestloop.c and nodeSubplan.c
integration?

Greetings,

Andres Freund