Re: READ COMMITTED vs. index-only scans

=?UTF-8?Q?Jacek_Ko=C5=82odziej?= <kolodziejj(at)gmail(dot)com> writes:
> Here's what happening to me: the "A" query occasionally (in my case: on the
> order of tenths per day) returns an ID _higher_ than any ID present in
> second query's result (other conditions I haven't specified do _not_ filter
> any more rows than "id <= max ID") - as if some entries were visible for
> the first query, but not for the second one. This is an inconsistency that
> is very problematic for me.

That sounds problematic to me too, but how certain are you that the "other
conditions you haven't specified" aren't suppressing the last row? That'd
certainly be the least surprising explanation. If it isn't that, though,
this surely seems like a bug.

Can you determine whether the row(s) missing in the second query are
freshly committed? Or have they been there awhile?

> Where am I wrong? What am I missing? What information may I provide to help
> with investigating this?

Probably the best thing to spend time on would be to try to extract a
publishable test case. It would be really hard to get to the bottom
of an issue like this without having a reproducer. It's okay if it
takes awhile to reproduce the fault ...

Also, before spending a whole lot of time on this: are you on 9.6.6?
If not, update, just in case this is an already-fixed issue. The
symptoms don't sound familiar, but I don't want to waste a lot of
time only to find out it's some manifestation of a known bug.

regards, tom lane