On 7/27/26 01:36, Michael Paquier wrote:
On Mon, Jun 01, 2026 at 03:30:58PM +0900, Kyotaro Horiguchi wrote:
I wonder whether strengthening the history-based matching would be
sufficient instead. If timelines with the same TLI but different
histories can be treated as distinct and pg_rewind continues walking
the history chain until it finds a common ancestor, that seems like a
fairly natural fit with the existing timeline model.
Yeah, perhaps there is something that we could do here better in
pg_rewind in terms of TLI history. A second software layer to ensure
TLI unicity feels just like a shortcut: we already have a LSN.
As Ants said, the LSN can easily be the same in both.
UUIDs would certainly make identification straightforward, although
they would also introduce longer identifiers that are a bit less
convenient for humans to work with. My initial thought is that it may
be worth exploring how far we can get with the existing history
information before introducing a new identifier.
This. For this reason, I am not convinced that this proposal is
neither acceptable or something that we need to do at all.
Why should we bear the burden of introducing a second level of
timeline identification knowing that by design we have to rely on a
*single* archive location for a new timeline selection when a standby
is triggered for promotion? My opinion is that this is trying to fix
a problem for something that it not actually a problem. If you play
with HA scenarios where there is a risk of two standbys reusing the
same timeline number, just don't do that. We've historically claimed
that the archive strategy is wrong if your deployments cannot
guarantee a unique TLI assignment. A new sub-identification system
will not provide more guarantees.
Having had to debug issues with pg_rewind and timelines in our
Kubernetes Operator these UUIDs would probably have helped me a lot.
Maybe the proposed fix is wrong (maybe like Ants says it does not got
far enough) but from personal experience I disagree with that there is
no problem here.
I will try to find time to play around with the patch and see if it
would have helped us.
--
Andreas Karlsson
Percona
