RE: Support logical replication of DDLs

On Tuesday, June 28, 2022 11:27 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> On Sun, Jun 26, 2022 at 11:47 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
> wrote:
> >
> > On 2022-Jun-22, vignesh C wrote:
> >
> > > 1) Creation of temporary table fails infinitely in the subscriber.
> > > CREATE TEMPORARY TABLE temp1 (a int primary key);
> > >
> > > The above statement is converted to the below format:
> > > CREATE TEMPORARY TABLE pg_temp.temp1 (a pg_catalog.int4 ,
> > > CONSTRAINT temp1_pkey PRIMARY KEY (a)); While handling the creation
> > > of temporary table in the worker, the worker fails continuously with
> > > the following error:
> > > 2022-06-22 14:24:01.317 IST [240872] ERROR: schema "pg_temp" does
> > > not exist
> >
> > Perhaps one possible fix is to change the JSON format string used in
> > deparse_CreateStmt. Currently, the following is used:
> >
> > + if (node->ofTypename)
> > + fmtstr = "CREATE %{persistence}s
> TABLE %{if_not_exists}s %{identity}D "
> > + "OF %{of_type}T %{table_elements}s "
> > + "%{with_clause}s %{on_commit}s %{tablespace}s";
> > + else
> > + fmtstr = "CREATE %{persistence}s
> TABLE %{if_not_exists}s %{identity}D "
> > + "(%{table_elements:, }s) %{inherits}s "
> > + "%{with_clause}s %{on_commit}s
> > + %{tablespace}s";
> > +
> > + createStmt =
> > + new_objtree_VA(fmtstr, 1,
> > + "persistence", ObjTypeString,
> > +
> > + get_persistence_str(relation->rd_rel->relpersistence));
> >
> > (Note that the word for the "persistence" element here comes straight
> > from relation->rd_rel->relpersistence.) Maybe it would be more
> > appropriate to set the schema to empty when the table is temp, since
> > the temporary-ness is in the %{persistence} element, and thus there is
> > no need to schema-qualify the table name.
> >
> >
> > However, that would still replicate a command that involves a
> > temporary table, which perhaps should not be considered fit for
> > replication. So another school of thought is that if the
> > %{persistence} is set to TEMPORARY, then it would be better to skip
> > replicating the command altogether.
> >
>
> +1. I think it doesn't make sense to replicate temporary tables.
> Similarly, we don't need to replicate the unlogged tables.

I agree that we don’t need to replicate temporary tables.

For unlogged table, one thing I noticed is that we always replicate the
DDL action on unlogged table in streaming replication. So, to be
consistent, maybe we need to generate WAL for DDL on unlogged table as
well ?

Best regards,
Hou zj