Re: brin regression test intermittent failures

Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> Evidently there is a problem right there. If I simply add an "order by
> tenthous" as proposed by Peter, many more errors appear; and what errors
> appear differs if I change shared_buffers. I think the real fix for
> this is to change the hand-picked values used in the brinopers table, so
> that they all pass the test using some reasonable ORDER BY specification
> in the populating query (probably tenk1.unique1).

I may be confused, but why would the physical ordering of the table
entries make a difference to the correct answers for this test?
(I can certainly see why that might break the brin code, but not
why it should change the seqscan's answers.)

Also, what I'd just noticed is that all of the cases that are failing are
ones where the expected number of matching rows is exactly 1. I am
wondering if the test is sometimes just missing random rows, and we're not
seeing any reported problem unless that makes it go down to no rows. (But
I do not know how that could simultaneously affect the seqscan case ...)

I think it would be a good idea to extend the brinopers table to include
the number of expected matches, and to complain if that's not what we got,
rather than simply checking for zero.

regards, tom lane