Re: WIP: Faster Expression Processing v4

On 2017-03-15 18:16:57 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2017-03-15 17:33:46 -0400, Tom Lane wrote:
> >> We could make the planner mark each table scan node with the highest
> >> column number that the plan will access, and use that to drive a
> >> slot_getsomeattrs call in advance of any access to tuple contents.
>
> > probably isn't sufficient - we build non-virtual tuples in a good number
> > of places (sorts, tuplestore using stuff like nodeMaterial, nodeHash.c
> > output, ...). I suspect it'd have measurable negative consequences if
> > we removed the deforming logic for all expressions/projections above
> > such nodes. I guess we could just do such a logic for every Plan node?
>
> [ scratches head... ] What deforming logic do you think I'm proposing
> removing?

I thought you were suggesting that we don't do the get_last_attnums (and
inlined version in the isSimpleVar case) at execution time anymore,
instead relying on logic in the planner to know how much to deform ahead
of time. Then we'd do slot_getsomeattrs in the appropriate places. But
I understood you suggesting to do so only in scan nodes - which doesn't
seem sufficient, due to the use of materialized / minimal tuples in
other types of nodes. Did I misunderstand?

- Andres