Re: [PATCH] Keeps tracking the uniqueness with UniqueKey

> On Fri, May 22, 2020 at 08:40:17AM +1200, David Rowley wrote:
>
> The way I picture the two working together is that the core UniqueKey
> patch adds UniqueKeys to RelOptInfos to allow us to have knowledge
> about what they're unique on based on the base relation's unique
> indexes.

Yep, I'm onboard with the idea.

> For Skipscans, that patch must expand on UniqueKeys to teach Paths
> about them.

That's already there.

> I imagine we'll set some required UniqueKeys during
> standard_qp_callback()

In standard_qp_callback, because pathkeys are computed at this point I
guess?

> and then we'll try to create some Skip Scan
> paths (which are marked with UniqueKeys) if the base relation does not
> already have UniqueKeys that satisfy the required UniqueKeys that were
> set during standard_qp_callback().

For a simple distinct query those UniqueKeys would be set based on
distinct clause. If I understand correctly, the very same is implemented
right now in create_distinct_paths, just after building all index paths,
so wouldn't it be just a duplication?

In general UniqueKeys in the skip scan patch were created from
distinctClause in build_index_paths (looks similar to what you've
described) and then based on them created index skip scan paths. So my
expectations were that the patch from this thread would work similar.