Re: Logical Replication of sequences - Mailing list pgsql-hackers

On Mon, Jun 10, 2024 at 12:43 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Mon, Jun 10, 2024 at 3:14 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Fri, Jun 7, 2024 at 7:30 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > >
> > > Are you imagining the behavior for sequences associated with tables
> > > differently than the ones defined by the CREATE SEQUENCE .. command? I
> > > was thinking that users would associate sequences with publications
> > > similar to what we do for tables for both cases. For example, they
> > > need to explicitly mention the sequences they want to replicate by
> > > commands like CREATE PUBLICATION ... FOR SEQUENCE s1, s2, ...; CREATE
> > > PUBLICATION ... FOR ALL SEQUENCES, or CREATE PUBLICATION ... FOR
> > > SEQUENCES IN SCHEMA sch1;
> > >
> > > In this, variants FOR ALL SEQUENCES and SEQUENCES IN SCHEMA sch1
> > > should copy both the explicitly defined sequences and sequences
> > > defined with the tables. Do you think a different variant for just
> > > copying sequences implicitly associated with tables (say for identity
> > > columns)?
> >
> > Oh, I was thinking that your proposal was to copy literally all
> > sequences by REPLICA/REFRESH SEQUENCE command.
> >

I am trying to keep the behavior as close to tables as possible.

> > But it seems to make
> > sense to explicitly specify the sequences they want to replicate. It
> > also means that they can create a publication that has only sequences.
> > In this case, even if they create a subscription for that publication,
> > we don't launch any apply workers for that subscription. Right?
> >

Right, good point. I had not thought about this.

> > Also, given that the main use case (at least as the first step) is
> > version upgrade, do we really need to support SEQUENCES IN SCHEMA and
> > even FOR SEQUENCE?
>

At the very least, we can split the patch to move these variants to a
separate patch. Once the main patch is finalized, we can try to
evaluate the remaining separately.

> Also, I guess that specifying individual sequences might not be easy
> to use for users in some cases. For sequences owned by a column of a
> table, users might want to specify them altogether, rather than
> separately. For example, CREATE PUBLICATION ... FOR TABLE tab1 WITH
> SEQUENCES means to add the table tab1 and its sequences to the
> publication. For other sequences (i.e., not owned by any tables),
> users might want to specify them individually.
>

Yeah, or we can have a syntax like CREATE PUBLICATION ... FOR TABLE
tab1 INCLUDE SEQUENCES.  Normally, we use the WITH clause for options
(For example, CREATE SUBSCRIPTION ... WITH (streaming=...)).

--
With Regards,
Amit Kapila.