On Mon, Nov 13, 2023 at 2:27 PM Andres Freund <andres@anarazel.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@snowman.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?