RE: Synchronizing slots from primary to standby

On Thursday, February 29, 2024 7:36 PM shveta malik <shveta.malik@gmail.com> wrote:
> 
> On Thu, Feb 29, 2024 at 7:04 AM Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>
> wrote:
> >
> > Here is the v101 patch set which addressed above comments.
> >
> 
> Thanks for the patch. Few comments:
> 
> 1)  Shall we mention in doc that shutdown will wait for standbys in
> standby_slot_names to confirm receiving WAL:
> 
> Suggestion for logicaldecoding.sgml:
> 
> When <varname>standby_slot_names</varname> is utilized, the primary
> server will not completely shut down until the corresponding standbys,
> associated with the physical replication slots specified in
> <varname>standby_slot_names</varname>, have confirmed receiving the
> WAL up to the latest flushed position on the primary server.
> 
> slot.c
> 2)
> /*
>  * If a logical slot name is provided in standby_slot_names, report
>  * a message and skip it. Although logical slots are disallowed in
>  * the GUC check_hook(validate_standby_slots), it is still
>  * possible for a user to drop an existing physical slot and
>  * recreate a logical slot with the same name.
>  */
> 
> This is not completely true, we can still specify a logical slot during instance
> start and it will accept it.
> 
> Suggestion:
> /*
>  * If a logical slot name is provided in standby_slot_names, report
>  * a message and skip it. It is possible for user to specify a
>  * logical slot name in standby_slot_names just before the server
>  * startup. The GUC check_hook(validate_standby_slots) can not
>  * validate such a slot during startup as the ReplicationSlotCtl
>  * shared memory is not initialized by that time. It is also
>  * possible for user to drop an existing physical slot and
>  * recreate a logical slot with the same name.
>  */
> 
> 3. Wait for physical standby to confirm receiving the given lsn
> 
> standby -->standbys
> 
> 
> 4.
> In StandbyConfirmedFlush(), is it better to have below errdetail in all
> problematic cases:
> Logical replication is waiting on the standby associated with \"%s\
> 
> We have it only for inactive pid case but we are waiting in all cases.

Thanks for the comments, I have addressed them.

Best Regards,
Hou zj