Re: Import Statistics in postgres_fdw before resorting to sampling.

>
> >> There's an advantage if we can combine stats across multiple relations
> >> - we don't have to sample children twice when analyzing the parent
> >> without ONLY. Instead we could produce parent statistics by combining
> >> statistics across children and the parent. To me this looks like
> >> altogether a different beast just like partial aggregates.
> >
> >
> > I think this patch is only ever going to get us out of 1 of the 2
> samples, which isn't ideal but it is a savings.
> >
>
> I am not suggesting to synthesize sample rows. Calculate the
> statistics of the parent table from that of its children.
>

I'm not sure we can actually do that. The functions that compute the
statistics are all based off of row samples, not already computed
statistics. I don't think we can synthesize a rowsample from the imported
statistics, at least not accurately. If I'm misunderstanding what you're
suggesting, please correct me.


> The note just mentions partition table but the limitation applies to
> any foreign child table.
>

Noted. Will fix in next revision.