Re: speed up a logical replica setup

On Sun, Jun 23, 2024 at 11:52 AM Noah Misch <noah@leadboat.com> wrote:
>
> > +static char *
> > +create_logical_replication_slot(PGconn *conn, struct LogicalRepInfo *dbinfo)
> > +{
> > +     PQExpBuffer str = createPQExpBuffer();
> > +     PGresult   *res = NULL;
> > +     const char *slot_name = dbinfo->replslotname;
> > +     char       *slot_name_esc;
> > +     char       *lsn = NULL;
> > +
> > +     Assert(conn != NULL);
> > +
> > +     pg_log_info("creating the replication slot \"%s\" on database \"%s\"",
> > +                             slot_name, dbinfo->dbname);
> > +
> > +     slot_name_esc = PQescapeLiteral(conn, slot_name, strlen(slot_name));
> > +
> > +     appendPQExpBuffer(str,
> > +                                       "SELECT lsn FROM pg_catalog.pg_create_logical_replication_slot(%s,
'pgoutput',false, false, false)", 
>
> This is passing twophase=false, but the patch does not mention prepared
> transactions.  Is the intent to not support workloads containing prepared
> transactions?  If so, the documentation should say that, and the tool likely
> should warn on startup if max_prepared_transactions != 0.
>

The other point to note in this regard is that if we don't support
two_phase in the beginning during subscription/slot setup, users won't
be able to change it as we don't yet support changing it via alter
subscription (though the patch to alter two_pc is proposed for PG18).

--
With Regards,
Amit Kapila.