Re: [PATCHES] Post-special page storage TDE support

On Mon, Nov 13, 2023 at 2:27 PM Andres Freund <andres(at)anarazel(dot)de> wrote:

> Hi,
>
> On 2023-11-08 18:47:56 -0800, Peter Geoghegan wrote:
> > On Wed, Nov 8, 2023 at 6:04 AM Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > > In conversations with folks (my memory specifically is a discussion
> with
> > > Peter G, added to CC, and my apologies to Peter if I'm misremembering)
> > > there was a pretty strong push that a page should be able to 'stand
> > > alone' and not depend on something else (eg: pg_control, or whatever)
> to
> > > provide info needed be able to interpret the page. For my part, I
> don't
> > > have a particularly strong feeling on that, but that's what lead to
> this
> > > design.
> >
> > The term that I have used in the past is "self-contained". Meaning
> > capable of being decoded more or less as-is, without any metadata, by
> > tools like pg_filedump.
>
> I'm not finding that very convincing - without cluster wide data, like
> keys, a
> tool like pg_filedump isn't going to be able to do much with encrypted
> pages. Given the need to look at some global data, figuring out the offset
> at
> which data starts based on a value in pg_control isn't meaningfully worse
> than
> having the data on each page.
>
> Storing redundant data in each page header, when we've wanted space in the
> page header for plenty other things, just doesn't seem a good use of said
> space.
>

This scheme would open up space per page that would now be available for
plenty of other things; the encoding in the header and the corresponding
available space in the footer would seem to open up quite a few options
now, no?