> >>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@momjian.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.vondra@2ndquadrant.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?
From:
Dave Cramer Date: Subject:
Re: let's make the list of reportable GUCs configurable (was Re: Add%r substitution for psql prompts to show recovery status)
