Re: [HACKERS] [COMMITTERS] pgsql: Fix freezing of a dead HOT-updatedtuple

On 2017-11-13 19:03:41 -0800, Andres Freund wrote:
> Hi,
> 
> On 2017-11-03 07:53:30 -0700, Andres Freund wrote:
> > Here's that patch.  I've stared at this some, and Robert did too. Robert
> > mentioned that the commit message might need some polish and I'm not
> > 100% sure about the error message texts yet.
> > 
> > I'm not yet convinced that the new elog in vacuumlazy can never trigger
> > - but I also don't think we want to actually freeze the tuple in that
> > case.
> 
> I'm fairly sure it could be triggered, therefore I've rewritten that.
> 
> I've played around quite some with the attached patch. So far, after
> applying the second patch, neither VACUUM nor VACUUM FULL / CLUSTER make
> the situation worse for already existing corruption. HOT pruning can
> change the exact appearance of existing corruption a bit, but I don't
> think it can make the corruption meaningfully worse.  It's a bit
> annoying and scary to add so many checks to backbranches but it kinda
> seems required.  The error message texts aren't perfect, but these are
> "should never be hit" type elog()s so I'm not too worried about that.
> 
> 
> Please review!

Please note:
I'd forgotten to git add the change to isolation_schedule re-activating
the freeze-the-dead regression test.

- Andres