RE: Enhance traceability of wal_level changes for backup management

On Sun, Mar 7, 2021 3:48 AM Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> wrote:
> On 28.01.21 01:44, osumi(dot)takamichi(at)fujitsu(dot)com wrote:
> >> (1) writing the time or LSN in the control file to indicate
> >> when/where wal_level is changed to 'minimal'
> >> from upper level to invalidate the old backups or make alerts to users.
> > I attached the first patch which implementes this idea.
> > It was aligned by pgindent and shows no regression.
>
> It's not clear to me what this is supposed to accomplish. I read the thread,
> but it's still not clear.
> What is one supposed to do with this information?
OK. The basic idea is to enable backup management
tools to recognize wal_level drop between *snapshots*.
When you have a snapshot of the cluster at one time and another one
at different time, with this new parameter, you can see if
anything that causes discontinuity from the drop happens
in the middle of the two snapshots without efforts to have a look at the WALs in between.

The new parameter is open to be monitored regularly
and if there's any change of that LSN, the tools can
take measures such as making an alert to users, taking a new backup
or invalidating past snapshots, which depends on the tools.

In the thread, we think the scenario of wal_level drop happens
when user wants to execute optimized bulk data loading.

Best Regards
Takamichi Osumi