Re: Duplicated LSN in ReorderBuffer

Hello,

On 2019-Sep-06, Andres Freund wrote:

> On 2019-08-19 08:51:43 -0700, Andres Freund wrote:
> > On August 19, 2019 7:43:28 AM PDT, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:

> > >Never mind.  I was able to reproduce it later, and verify that Andres'
> > >proposed strategy doesn't seem to fix the problem.  I'm going to study
> > >the problem again today.
> > 
> > Could you post the patch?

Here's a couple of patches.

always_decode_assignment.patch is Masahiko Sawada's patch, which has
been confirmed to fix the assertion failure.

assign-child.patch is what I understood you were proposing -- namely to
assign the subxid to the top-level xid on NEW_CID.  In order for it to
work at all, I had to remove a different safety check; but the assertion
still hits when running Ildar's test case.  So the patch doesn't
actually fix anything.  And I think it makes sense that it fails, since
the first thing that's happening in this patch is that we create both
the top-level xact and the subxact with the same LSN value, which is
what triggers the assertion in the first place.  It's possible that I
misunderstood what you were suggesting.

If you want to propose a different fix, be my guest, but failing that
I'm inclined to push always_decode_assignment.patch sometime before the
end of the week.

Thanks,

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