Hi Stephen, On Tue, Jan 12, 2021 at 10:47 AM Stephen Frost <sfr...@snowman.net> wrote:
> > This is an interesting question but ultimately I don't think we should > be looking at this from the perspective of allowing arbitrary changes to > the page format. The challenge is that much of the page format, today, > is defined by a C struct and changing the way that works would require a > great deal of code to be modified and turn this into a massive effort, > assuming we wish to have the same compiled binary able to work with both > unencrypted and encrypted clusters, which I do believe is a requirement. > > The thought that I had was to, instead, try to figure out if we could > fudge some space by, say, putting a 128-bit 'hole' at the end of the > page and just move pd_special back, effectively making the page seem > 'smaller' to all of the code that uses it, except for the code that > knows how to do the decryption. I ran into some trouble with that but > haven't quite sorted out what happened yet. Other ideas would be to put > it before pd_special, or maybe somewhere else, but a lot depends on the > code's expectations. > > I agree that we should not make too many changes to affect the use of unencrypted clusters. But as a personal opinion only, I don't think it's a good idea to add some "implicit" tricks. To provide an inspiration, can we add a flag to mark whether the page format has been changed: --- a/src/include/storage/bufpage.h +++ b/src/include/storage/bufpage.h @@ -181,8 +185,9 @@ typedef PageHeaderData *PageHeader; #define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */ #define PD_ALL_VISIBLE 0x0004 /* all tuples on page are visible to * everyone */ +#define PD_PAGE_ENCRYPTED 0x0008 /* Is page encrypted? */ -#define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */ +#define PD_VALID_FLAG_BITS 0x000F /* OR of all valid pd_flags bits */ /* * Page layout version number 0 is for pre-7.3 Postgres releases. @@ -389,6 +394,13 @@ PageValidateSpecialPointer(Page page) #define PageClearAllVisible(page) \ (((PageHeader) (page))->pd_flags &= ~PD_ALL_VISIBLE) +#define PageIsEncrypted(page) \ + (((PageHeader) (page))->pd_flags & PD_PAGE_ENCRYPTED) +#define PageSetEncrypted(page) \ + (((PageHeader) (page))->pd_flags |= PD_PAGE_ENCRYPTED) +#define PageClearEncrypted(page) \ + (((PageHeader) (page))->pd_flags &= ~PD_PAGE_ENCRYPTED) + #define PageIsPrunable(page, oldestxmin) \ ( \ AssertMacro(TransactionIdIsNormal(oldestxmin)), \ In this way, I think it has little effect on the unencrypted cluster, and we can also modify the page format as we wish. Of course, it's also possible that I didn't understand your design correctly, or there's something wrong with my idea. :D -- There is no royal road to learning. HighGo Software Co.
