RE: Data is copied twice when specifying both child and parent table in publication

Hi,

When reviewing some logical replication related features. I noticed another
possible problem if the subscriber subscribes multiple publications which
publish parent and child table.

For example:

----pub
create table t (a int, b int, c int) partition by range (a);
create table t_1 partition of t for values from (1) to (10);

create publication pub1 for table t
  with (PUBLISH_VIA_PARTITION_ROOT);
create publication pub2 for table t_1
  with (PUBLISH_VIA_PARTITION_ROOT);

----sub
---- prepare table t and t_1
CREATE SUBSCRIPTION sub CONNECTION 'port=10000 dbname=postgres' PUBLICATION pub1, pub2;

select * from pg_subscription_rel ;
 srsubid | srrelid | srsubstate | srsublsn
---------+---------+------------+-----------
   16391 |   16385(t) | r          | 0/150D100
   16391 |   16388(t_1) | r          | 0/150D138

If subscribe two publications one of them publish parent table with
(pubviaroot=true) and another publish child table. Both the parent table and
child table will exist in pg_subscription_rel which also means we will do
initial copy for both tables.

But after initial copy, we only publish change with the schema of the parent
table(t). It looks a bit inconsistent.

Based on the document of PUBLISH_VIA_PARTITION_ROOT option. I think the
expected behavior could be we only store the top most parent(table t) in
pg_subscription_rel and do initial copy for it if pubviaroot is on. I haven't
thought about how to fix this and will investigate this later.

Best regards,
Hou zj