Date: Tue, 12 Sep 2017 14:41:36 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>, "Wood, Dan" <hexpert@amazon.com>,
	"pgsql-bugs@postgresql.org" <pgsql-bugs@postgresql.org>,
	Andres Freund <andres@anarazel.de>,
	"Wong, Yi Wen" <yiwong@amazon.com>
Subject: Re: Old row version in hot chain become visible after a freeze
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Michael Paquier wrote:
> On Tue, Sep 12, 2017 at 5:22 PM, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > Michael Paquier wrote:
> >> On Mon, Sep 11, 2017 at 11:01 PM, Alvaro Herrera
> >> <alvherre@alvh.no-ip.org> wrote:
> >> > (I also threw in a small sleep between heap_page_prune and
> >> > HeapTupleSatisfiesVacuum while testing, just to widen the problem window
> >> > to hopefully make any remaining problems more evident.)
> >>
> >> I am understanding that you mean heap_prepare_freeze_tuple here
> >> instead of heap_page_prune.
> >
> > Hmm ... no, I meant adding a sleep after the page is pruned, before
> > HeapTupleSatisfiesVacuum call that determines the action with regards to
> > freezing.
> 
> Well, I have tested both. With the test case of Dan adding a sleep
> after calling HeapTupleSatisfiesVacuum() helped in increasing the
> window. Of course feel free to correct me.

OK, great, thanks for testing.


> > I bet those are multixact values rather than garbage.  You should see
> > HEAP_XMAX_IS_MULTI in t_infomask in those cases, and the values should
> > be near NextMultiXactId (make sure to checkpoint if you examine with
> > pg_controldata; I think it's easier to obtain it from shmem.  Or you
> > could just use pg_get_multixact_members()).
> 
> Yes, you're right. That's the case. So I guess that I don't have much
> complains about the patch as presented.

Thanks for the confirmation.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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