On Thu, Jul 11, 2019 at 03:47:50PM -0400, Robert Haas wrote:
> On Tue, Jul 9, 2019 at 10:43 AM Bruce Momjian <bruce@momjian.us> wrote:
> > FYI, pg_upgrade already preserves the pg_class.oid, which is why I
> > recommended it over pg_class.relfilenode:
>
> I think it's strange that pg_upgrade does not preserve the
> relfilenode. I think it would probably make more sense if it did.
>
> Anyway, leaving that aside, you have to be able to read pg_class to
> know the OID of a table, and you can't do that in recovery before
> reaching consistency. Yet, you still need to be able to modify disk
> blocks at that point, to finish recovery. So I can't see how any
> system that involves figuring out the nonce from the OID would ever
> work.
>
> If we end up with random nonces, we're going to have to store them
> someplace - either in some unencrypted portion of the disk blocks
> themselves, or in a separate fork, or someplace else. If it's OK for
> them to predictable as long as they vary a lot, we could derive them
> from DBOID + RELFILENODE + FORK + BLOCK, but not from DBOID + RELOID +
> FORK + BLOCK, because of the aforementioned recovery problem.
Later in this thread, we decided that the page LSN was the best option
as a nonce because it changes every time the page chages. (We will
enable wal_log_hints.) We will not encrypt the first 16 bytes of the
page so it can be used for the nonce. (AES block ciphers are use 16-byte
blocks.)
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
