Thomas Munro wrote:
> On Tue, Jun 2, 2015 at 9:30 AM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > My guess is that the file existed, and perhaps had one or more pages,
> > but the wanted page doesn't exist, so we tried to read but got 0 bytes
> > back. read() returns 0 in this case but doesn't set errno.
> >
> > I didn't find a way to set things so that the file exists but is of
> > shorter contents than oldestMulti by the time the checkpoint record is
> > replayed.
>
> I'm just starting to learn about the recovery machinery, so forgive me
> if I'm missing something basic here, but I just don't get this. As I
> understand it, offsets/0046 should either have been copied with that
> page present in it if it existed before the backup started (apparently
> not in this case), or extended to contain it by WAL records that come
> after the backup label but before the checkpoint record that
> references it (also apparently not in this case).
Exactly --- that's the spot at which I am, also. I have had this
spinning in my head for three days now, and tried every single variation
that I could think of, but like you I was unable to reproduce the issue.
However, our customer took a second base backup and it failed in exactly
the same way, module some changes to the counters (the file that
didn't exist was 004B rather than 0046). I'm still at a loss at what
the failure mode is. We must be missing some crucial detail ...
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
