Re: pgstatindex vs. !indisready

On Mon, Oct 02, 2023 at 09:24:33AM +0900, Michael Paquier wrote:
> On Sun, Oct 01, 2023 at 04:20:42PM -0700, Peter Geoghegan wrote:
> > On Sun, Oct 1, 2023 at 2:00 PM Noah Misch <noah@leadboat.com> wrote:
> >> [brin_desummarize_range brin_summarize_new_values brin_summarize_range
> >> gin_clean_pending_list] currently succeed.  I propose to make them emit a
> >> DEBUG1 message and return early, like amcheck does, except on !indisready.
> >> This would allow users to continue running them on all indexes of the
> >> applicable access method.  Doing these operations on an
> >> indisready&&!indisvalid index is entirely reasonable, since they relate to
> >> INSERT/UPDATE/DELETE operations.
> 
> Hmm.  Still slightly incorrect in some cases?  Before being switched
> to indisvalid, an index built concurrently may miss some tuples
> deleted before the reference snapshot used to build the index was
> taken.

The !indisvalid index may be missing tuples, yes.  In what way does that make
one of those four operations incorrect?