Re: pg_sequence_last_value() for unlogged sequences on standbys

On Sat, May 04, 2024 at 06:45:32PM +0900, Michael Paquier wrote:
> On Fri, May 03, 2024 at 05:22:06PM -0400, Tom Lane wrote:
>> Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
>>> IIUC this would cause other sessions' temporary sequences to appear in the
>>> view. Is that desirable?
>>
>> I assume Michael meant to move the test into the C code, not drop
>> it entirely --- I agree we don't want that.
>
> Yup. I meant to remove it from the script and keep only something in
> the C code to avoid the duplication, but you're right that the temp
> sequences would create more noise than now.
>
>> Moving it has some attraction, but pg_is_other_temp_schema() is also
>> used in a lot of information_schema views, so we couldn't get rid of
>> it without a lot of further hacking. Not sure we want to relocate
>> that filter responsibility in just one view.
>
> Okay.

Okay, so are we okay to back-patch something like v1? Or should we also
return NULL for other sessions' temporary schemas on primaries? That would
change the condition to something like

char relpersist = seqrel->rd_rel->relpersistence;

if (relpersist == RELPERSISTENCE_PERMANENT ||
(relpersist == RELPERSISTENCE_UNLOGGED && !RecoveryInProgress()) ||
!RELATION_IS_OTHER_TEMP(seqrel))
{
...
}

I personally think that would be fine to back-patch since pg_sequences
already filters it out anyway.

--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com