Re: Synchronizing slots from primary to standby

On Wed, Mar 6, 2024 at 5:53 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Mar 6, 2024 at 12:07 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Fri, Mar 1, 2024 at 3:22 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> > >
> > > On Fri, Mar 1, 2024 at 5:11 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > ...
> > > > + /*
> > > > + * "*" is not accepted as in that case primary will not be able to know
> > > > + * for which all standbys to wait for. Even if we have physical slots
> > > > + * info, there is no way to confirm whether there is any standby
> > > > + * configured for the known physical slots.
> > > > + */
> > > > + if (strcmp(*newval, "*") == 0)
> > > > + {
> > > > + GUC_check_errdetail("\"*\" is not accepted for
> > > > standby_slot_names");
> > > > + return false;
> > > > + }
> > > >
> > > > Why only '*' is checked aside from validate_standby_slots()? I think
> > > > that the doc doesn't mention anything about '*' and '*' cannot be used
> > > > as a replication slot name. So even if we don't have this check, it
> > > > might be no problem.
> > > >
> > >
> > > Hi, a while ago I asked this same question. See [1 #28] for the response..
> >
> > Thanks. Quoting the response from the email:
> >
> > SplitIdentifierString() does not give error for '*' and '*' can be considered
> > as valid value which if accepted can mislead user that all the standbys's slots
> > are now considered, which is not the case here. So we want to explicitly call
> > out this case i.e. '*' is not accepted as valid value for standby_slot_names.
> >
> > IIUC we're concerned with a case like where the user confused
> > standby_slot_names values with synchronous_standby_names values. Which
> > means we would need to keep thath check consistent with available
> > values of synchronous_standby_names.
> >
>
> Both have different formats to specify. For example, for
> synchronous_standby_names we have the following kind of syntax to
> specify:
> [FIRST] num_sync ( standby_name [, ...] )
> ANY num_sync ( standby_name [, ...] )
> standby_name [, ...]
>
> I don't think we can have a common check for both of them as the
> specifications are different. In fact, I don't think we need a special
> check for '*'.

I think so too.

> The user will anyway get a WARNING at a later point
> that the replication slot with that name doesn't exist.

Right.

Regards,

--
Masahiko Sawada
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