Here is a first attempt at a WIP patch. Sorry about the MIME type.
It doesn't take any locks on the tables, but I'm not super confident
that that's safe, so any input would be appreciated.
I omitted view support for simplicity, but if that seems like a
requirement I'll see about adding it. I assume we would need to take
AccessShareLock on views (and release it, per above).
If the syntax and behavior seem roughly correct I'll work on updating the docs.
The commit message at the beginning of the .patch has slightly more commentary.
Thanks for any and all feedback!