Hi,
On 9/29/23 1:33 PM, Amit Kapila wrote:
On Thu, Sep 28, 2023 at 6:31 PM Drouvot, Bertrand
<bertranddrouvot...@gmail.com> wrote:
I think that standby_slot_names could be used to do some filtering (means
for which standby(s) we don't want the logical replication on the primary to go
ahead and for which standby(s) one would allow it).
Isn't it implicit that the physical standby that has requested
'synchronize_slot_names' should be ahead of their corresponding
logical walsenders? Otherwise, after the switchover to the new
physical standby, the logical subscriptions won't work.
Right, but the idea was to let the flexibility to bypass this constraint. Use
case was to avoid a physical standby being down preventing the decoding
on the primary.
I think that removing the GUC would:
- remove this flexibility
I think if required we can add such a GUC later as well. Asking users
to set more parameters also makes the feature less attractive, so I am
trying to see if we can avoid this GUC.
Agree but I think we have to address the standby being down case.
- probably open corner cases like: what if a standby is down? would that mean
that synchronize_slot_names not being send to the primary would allow the
decoding
on the primary to go ahead?
Good question. BTW, irrespective of whether we have
'standby_slot_names' parameters or not, how should we behave if
standby is down? Say, if 'synchronize_slot_names' is only specified on
standby then in such a situation primary won't be even aware that some
of the logical walsenders need to wait.
Exactly, that's why I was thinking keeping standby_slot_names to address
this scenario. In such a case one could simply decide to keep or remove
the associated physical replication slot from standby_slot_names. Keep would
mean "wait" and removing would mean allow to decode on the primary.
OTOH, one can say that users
should configure 'synchronize_slot_names' on both primary and standby
but note that this value could be different for different standby's,
so we can't configure it on primary.
Yeah, I think that's a good use case for standby_slot_names, what do you think?
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
