I've pushed Anastasia's patch to support index-only scans with GiST, and
it's time to add opclasses support for all the opclasses that are not
lossy. I think at least all the btree_gist opclasses need to be
supported, it would be pretty surprising if they didn't support
index-only scans, while some more complex opclasses did.
Attached is a WIP patch for that. It covers all the varlen types that
btree_gist supports, and int2, int4 and oid. The rest of the fixed-width
types should be just a matter of copy-pasting. I'll continue adding
those, but wanted to let people know I'm working on this.
- Heikki