Hi, On 2023-11-13 14:37:47 -0600, David Christensen wrote: > On Mon, Nov 13, 2023 at 2:27 PM Andres Freund <and...@anarazel.de> wrote: > > On 2023-11-08 18:47:56 -0800, Peter Geoghegan wrote: > > > On Wed, Nov 8, 2023 at 6:04 AM Stephen Frost <sfr...@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?
Sure, if you're willing to rewrite the whole cluster to upgrade and willing to permanently sacrifice some data density. If the stored data is actually specific to the page - that is the place to put the data. If not, then the tradeoff is much more complicated IMO. Of course this isn't a new problem - storing the page size on each page was just silly, it's never going to change across the cluster and even more definitely not going to change within a single relation. Greetings, Andres Freund
