Re: Enhance traceability of wal_level changes for backup management

On 3/7/21 9:45 PM, osumi(dot)takamichi(at)fujitsu(dot)com wrote:
> 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.

As a backup software author, I don't see this feature as very useful.

The problem is that there are lots of ways for WAL to go missing so
monitoring the WAL archive for gaps is essential and this feature would
not replace that requirement. The only extra information you'd get is
the ability to classify the most recent gap as "intentional", maybe.

So, -1 from me.

Regards,
--
-David
david(at)pgmasters(dot)net