I wrote:
> The other index AMs do that during the first amgettuple or amgetbitmap
> call, but it doesn't look like there is any convenient way to duplicate
> that behavior in spgist; none of the code in or below spggettuple or
> spggetbitmap is explicitly aware of whether this is the first call.
> I'm inclined to propose adding the counter bump in spgrescan. That
> isn't *exactly* equivalent semantics, but it would only matter if
> someplace called amrescan and then didn't follow through with a scan.
> The attached seems to behave as I'd expect.
I had a nagging feeling that we might have multiple amrescan calls
in some code paths, but after reviewing the commit log, it looks
like that stopped being an issue in 9.1 (commit d583f10b7).
So it should be okay to do it like this in supported branches.
regards, tom lane