Re: [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

Peter Geoghegan wrote:
> On Sat, Oct 7, 2017 at 1:31 AM, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> >> As you must have seen, Alvaro said he has a variant of Dan's original
> >> script that demonstrates that a problem remains, at least on 9.6+,
> >> even with today's fix. I think it's the stress-test that plays with
> >> fillfactor, many clients, etc [1].
> >
> > I just execute setup.sql once and then run this shell command,
> >
> > while :; do
> > psql -e -P pager=off -f ./repro.sql
> > for i in `seq 1 5`; do
> > psql -P pager=off -e --no-psqlrc -f ./lock.sql &
> > done
> > wait && psql -P pager=off -e --no-psqlrc -f ./reindex.sql
> > psql -P pager=off -e --no-psqlrc -f ./report.sql
> > echo "done"
> > done
>
> I cannot reproduce the problem on my personal machine using this
> script/stress-test. I tried to do so on the master branch git tip.
> This reinforces the theory that there is some timing sensitivity,
> because the remaining race condition is very narrow.

Hmm, I think I added a random sleep (max. 100ms) right after the
HeapTupleSatisfiesVacuum call in vacuumlazy.c (lazy_scan_heap), and that
makes the race easier to hit.

--
Álvaro Herrera https://www.2ndQuadrant.com/
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