Re: FSM corruption and standby servers

On Mon, Oct 31, 2016 at 12:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> "Hunley, Douglas" <douglas(dot)hunley(at)openscg(dot)com> writes:
> > On Mon, Oct 31, 2016 at 10:38 AM, Tim Goodaire <tgoodaire(at)dyn(dot)com>
> wrote:
> >> I have a question regarding the FSM corruption bug that is fixed in
> >> postgresql 9.5.5 (https://wiki.postgresql.org/
> wiki/Free_Space_Map_Problems).
> >> If I don't find any corruption on a master database, is it still
> possible
> >> that there is corruption on the standbys?
>
> > It shouldn't be, iirc. FSMs are only ever created/updated by vacuum,
> which
> > doesn't run on a slave until it is promoted to a master.
>
> The problem is that the WAL data can be wrong in these cases, and since
> the standbys only know what they were told in the WAL stream, their images
> will be wrong even if the master is valid.
>
> I would have thought that the referenced page is clear enough about
> needing to check the standbys; do you think it isn't?
>

The page does clearly say that you need to check standby databases as well.
The bit that I was unsure of is whether the absence of corruption on the
master was evidence that this problem has not affected the standbys.

--
Tim Goodaire
Database Engineer
Dyn, Inc
tgoodaire(at)dyn(dot)com
M: 603-264-6642