Re: [v9.5] Custom Plan API

* Simon Riggs (simon(at)2ndQuadrant(dot)com) wrote:
> On 7 May 2014 17:43, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > It's the optimizer's job to figure out which path to pick though, based
> > on which will have the lowest cost.
>
> Of course. I'm not suggesting otherwise.
>
> >> If do you want that, you can write an Event Trigger that automatically
> >> adds a lookaside for any table.
> >
> > This sounds terribly ugly and like we're pushing optimization decisions
> > on to the user instead of just figuring out what the best answer is.
>
> I'm proposing that we use a declarative approach, just like we do when
> we say CREATE INDEX.

There's quite a few trade-offs when it comes to indexes though. I'm
trying to figure out when you wouldn't want to use a GPU, if it's
available to you and the cost model says it's faster? To me, that's
kind of like saying you want a declarative approach for when to use a
HashJoin.

> The idea is that we only consider a lookaside when a lookaside has
> been declared. Same as when we add an index, the optimizer considers
> whether to use that index. What we don't want to happen is that the
> optimizer considers a GIN plan, even when a GIN index is not
> available.

Yes, I understood your proposal- I just don't agree with it. ;)

For MatViews and/or Indexes, there are trade-offs to be had as it
relates to disk space, insert speed, etc.

Thanks,

Stephen