Greetings, * Bruce Momjian (br...@momjian.us) wrote: > On Tue, Jan 12, 2021 at 01:11:29PM -0500, Stephen Frost wrote: > > > I think one big question is that, since we are using a streaming cipher, > > > do we care about hint bit changes showing to users? I actually don't > > > know. If we do, some kind of dummy LSN record might be required, as you > > > suggested. > > > > I don't think there's any doubt that we need to make sure that the IV is > > distinct and advancing the LSN to get a new one when needed for this > > case seems like it's probably the way to do that. Hint bit change > > visibility to users isn't really at issue here- we can't use the same IV > > multiple times. The two options that we have are to either not actually > > update the hint bit in such a case, or to make sure to change the > > LSN/IV. Another option would be to, if we're able to make a hole to put > > the GCM tag on to the page somewhere, further widen that hole to include > > an additional space for a counter that would be mixed into the IV, to > > avoid having to do an XLOG NOOP. > > Well, we have eight unused bits in the IV, so we could just increment > that for every hint bit change that uses the same LSN, and then force a > dummy WAL record when that 8-bit counter overflows --- that seems > simpler than logging hint bits.
Sure, as long as we have a place to store that information.. We need to have the full IV available when we go to decrypt the page. Thanks, Stephen
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