RE: Initial COPY of Logical Replication is too slow

Dear Sawada-san,

Thanks for updating the patch. I think the patch has a good shape.
Below contains minor comments.

```
+ if (filter_by_relid)
+ relkind = get_rel_relkind(target_relid);
```

Can we return here if the relkind is not RELKIND_RELATION nor RELKIND_PARTITIONED_TABLE?
Key assumption here is that pg_get_publication_tables_b() returns at most one
tuple, thus this is would be called only once.

```
+ /*
+ * Non-alltables
+ */
+ if (relispartition)
```

else-if might be usalbe to clarify we're in the non-alltables case.

```
+ Assert(pubnames != NULL);
```

Personally I prefer to do Assert() before the SRF_FIRSTCALL_INIT(). Because it's
only related with argument and not related with other function calls.

```
+ proname => 'pg_get_publication_tables', prorows => '10',
```

Can prorows be 1? Because only a row would be returned here.

Best regards,
Hayato Kuroda
FUJITSU LIMITED