Re: Remove secondary checkpoint

On 2017-10-30 10:10:19 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > I was mostly just thinking out loud, listing another option rather
> > than advocating for it.
>
> FWIW, I just wanted the question to be debated and resolved properly.
>
> After rereading the thread Andres pointed to, I thought of a hazard
> that I think Andres alluded to, but didn't spell out explicitly:
> if we can't read the primary checkpoint, and then back up to a
> secondary one and replay as much of WAL as we can read, we may well
> be left with an inconsistent database.

Exactly.

> I'm content now that removing the secondary checkpoint is an OK
> decision. (This isn't a review of Simon's patch, though.)

I wonder if we shouldn't add a pg_resetxlog option that sets the
checkpoint to start from to a certain LSN. For the few cases where
there's actual data recovery needed that's a lot more useful than
randomly using checkpoint - 1. And it's an explicit expert only thing,
without costing everyone.

Greetings,

Andres Freund