There seems to be some considerable imprecision in the timing of -P
progress reports.  Nominally each thread ought to produce 2 reports
in this test, but about 10% of the time we only get one, and 1% of
the time we get three, as per buildfarm results so far.  Pending
further investigation, treat the last case as a "pass".  (I, tgl,
am suspicious that this still might not be lax enough, now that it's
obvious that the behavior is load-dependent; but there's not yet
buildfarm evidence to confirm that suspicion.)

Fabien Coelho

Discussion: https://postgr.es/m/26654.1505232433@sss.pgh.pa.us