Re: pageinspect get_raw_page() option to return invalid pages

On 2018-05-04 11:53:25 -0700, Peter Geoghegan wrote:
> On Fri, May 4, 2018 at 11:46 AM, Andres Freund <andres@anarazel.de> wrote:
> > Could you expand on that? Are you envisioning an option to
> > ReadBufferExtended()? Because that's certainly not what I'm thinking of
> > - it seems dangerous to populate shared buffers with an invalid
> > page. Therefore I was more thinking to falling back to smgrread() or
> > such.
> 
> I'm not envisaging anything specific just yet. It would be nice if
> amcheck had an option that bypassed shared_buffers, because users want
> that. That's all.

Can you expand on what they want?

- Avoid polluting caches? Why's the ringbuffer logic not good enough?
- Continue after a checksum or similar failure? That seems a bit useless
  for amcheck imo? You know there's corruption at that point after all.
- Read on disk data, bypassing shared buffers? That'd present a lot of
  coherency issues, no?

Greetings,

Andres Freund