Re: index-only scans

Robert Haas <robertmhaas@gmail.com> writes:
> Have you given any thought to what would be required to support
> index-only scans on non-btree indexes - particularly, GIST?  ISTM we
> might have had a thought that some GIST opclasses but not others would
> be able to regurgitate tuples, or maybe even that it might vary from
> index tuple to index tuple.  But that discussion was a long time ago,
> and my memory is fuzzy.

It would have to be a per-opclass property, for sure, since the basic
criterion is whether the opclass's "compress" function is lossy.
I don't think we can tolerate a situation where some of the index tuples
might be able to yield data and others not --- that would undo all the
improvements I've been working on over the past few days.

I haven't thought as far ahead as how we might get the information
needed for a per-opclass flag.  A syntax addition to CREATE OPERATOR
CLASS might be the only way.
        regards, tom lane