Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS)

> >>Uh, what if a transaction modifies page 0 and page 1 of the same table

> >>--- don't those pages have the same LSN.
> >
> >No, because WAL being a physical change log, each page gets its own
> >WAL record with its own LSN.
> >
>
> What if you have wal_log_hints=off? AFAIK that won't change the page LSN.
>

> Alvaro suggested elsewhere that we require checksums for these, which
> would also force wal_log_hints to be on, and therefore the LSN would
> change.

Yes, it sounds like the agreement was LSN is unique when wal_log_hints is
on. I don't know enough about the internals to know if pg_class.oid is
also needed or not.

Ryan

On Wed, Jul 10, 2019 at 6:07 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> On Thu, Jul 11, 2019 at 12:18:47AM +0200, Tomas Vondra wrote:
> > On Wed, Jul 10, 2019 at 06:04:30PM -0400, Stephen Frost wrote:
> > > Greetings,
> > >
> > > * Tomas Vondra (tomas(dot)vondra(at)2ndquadrant(dot)com) wrote:
> > > > On Wed, Jul 10, 2019 at 04:11:21PM -0400, Alvaro Herrera wrote:
> > > > >On 2019-Jul-10, Bruce Momjian wrote:
> > > > >
> > > > >>Uh, what if a transaction modifies page 0 and page 1 of the same
> table
> > > > >>--- don't those pages have the same LSN.
> > > > >
> > > > >No, because WAL being a physical change log, each page gets its own
> > > > >WAL record with its own LSN.
> > > > >
> > > >
> > > > What if you have wal_log_hints=off? AFAIK that won't change the page
> LSN.
> > >
> > > Alvaro suggested elsewhere that we require checksums for these, which
> > > would also force wal_log_hints to be on, and therefore the LSN would
> > > change.
> > >
> >
> > Oh, I see - yes, that would solve the hint bits issue. Not sure we want
> > to combine the features like this, though, as it increases the costs of
> > TDE. But maybe it's the best solution.
>
> Uh, why can't we just force log_hint_bits for encrypted tables? Why
> would we need to use checksums as well?
>
> Why is page-number not needed in the nonce? Because it is duplicative
> of the LSN? Can we use just LSN? Do we need pg_class.oid too?
>
> --
> Bruce Momjian <bruce(at)momjian(dot)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 +
>