Greetings, * Robert Haas (robertmh...@gmail.com) wrote: > On Thu, Oct 7, 2021 at 1:09 PM Bruce Momjian <br...@momjian.us> wrote: > > Are you saying a base backup could read a page from the file system and > > see a partial write, even though the write is written as 8k? I had not > > thought about that. > > Yes; see my other response.
Yes, that is something that has been seen before. > > I think this whole discussion is about whether we need full page images > > for hint bit changes. I think we do if we use the LSN for the nonce (in > > the old patch), and probably need it for hint bit changes when using > > block cipher modes (XTS) if we feel basebackup could read only part of a > > 16-byte page change. > > I think all the encryption modes that we're still considering have the > (very desirable) property that changing a single bit of the > unencrypted page perturbs the entire output. But that just means that > encrypted clusters will have to run in the same mode as clusters with > checksums, or clusters with wal_log_hints=on, features which the > community has already accepted as having reasonable overhead. I have > in the past expressed skepticism about whether that overhead is really > small enough to be considered acceptable, but if I recall correctly, > the test results posted to the list suggest that you need a working > set just a little bit large than shared_buffers to make it really > sting. And that's not a super-common thing to do. Anyway, if people > aren't screaming about the overhead of that system now, they're not > likely to complain about applying it to some new situation either. Agreed. Thanks, Stephen
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