Re: Allowing ALTER TYPE to change storage strategy

"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> Is there also an issue with whether the type has implemented compression or
> not - i.e., should the x->e and m->e paths be forbidden too? Or is it
> always the case a non-plain type is compressible and the other non-plain
> options just switch between preferences (so External just says "while I can
> be compressed, please don't")?

Yeah, the only relevant issue here is "can it be toasted, or not?". A
data type doesn't have direct control of which toasting options can be
applied, nor does it need to, as long as the C functions apply the
correct detoast macros.

> Can you please include an edit to [1] indicating that "e" is the
> abbreviation for External and "x" is Extended (spelling out the other two
> as well). Might be worth a comment at [2] as well.
> [1] https://www.postgresql.org/docs/12/catalog-pg-type.html
> [2] https://www.postgresql.org/docs/12/storage-toast.html

Done in [1]; I didn't see much point in changing [2].

regards, tom lane