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

On Thu, Oct 5, 2017 at 10:39 AM, Wood, Dan <hexpert(at)amazon(dot)com> wrote:
> Whatever you do make sure to also test 250 clients running lock.sql. Even with the communities fix plus YiWen’s fix I can still get duplicate rows. What works for “in-block” hot chains may not work when spanning blocks.

Interesting. Which version did you test? Only 9.6?

> Once nearly all 250 clients have done their updates and everybody is waiting to vacuum which one by one will take a while I usually just “pkill -9 psql”. After that I have many of duplicate “id=3” rows. On top of that I think we might have a lock leak. After the pkill I tried to rerun setup.sql to drop/create the table and it hangs. I see an autovacuum process starting and existing every couple of seconds. Only by killing and restarting PG can I drop the table.

Yeah, that's more or less what I have been doing. My tests involve
using your initial script with way more sessions triggering lock.sql,
minus the kill-9 portion (good idea actually). I can of course see the
sessions queuing for VACUUM, still I cannot see duplicated rows, even
if I headshot Postgres in the middle of the VACUUM waiting queue. Note
that I have just tested Alvaro's patch on 9.3.
--
Michael