Multiple primary key on partition table?

Hi,

I am able to create multiple primary key on partition table by executing below statement.

[edb@localhost bin]$ ./psql postgres
psql (11beta3)
Type "help" for help.

postgres=# CREATE TABLE t1 (a int PRIMARY KEY,b int) PARTITION BY RANGE (a);
CREATE TABLE
postgres=# CREATE TABLE t1_p1 PARTITION OF t1 (b PRIMARY KEY) FOR VALUES FROM (MINVALUE) TO (MAXVALUE);
CREATE TABLE
postgres=# \d+ t1_p1
                                   Table "public.t1_p1"
 Column |  Type   | Collation | Nullable | Default | Storage | Stats target | Description
--------+---------+-----------+----------+---------+---------+--------------+-------------
 a      | integer |           | not null |         | plain   |              |
 b      | integer |           | not null |         | plain   |              |
Partition of: t1 FOR VALUES FROM (MINVALUE) TO (MAXVALUE)
Partition constraint: (a IS NOT NULL)
Indexes:
    "t1_p1_pkey" PRIMARY KEY, btree (a)
    "t1_p1_pkey1" PRIMARY KEY, btree (b)

Is this fine to allow it?

eventually it cause to pg_upgrade failed with below error.

pg_restore: creating TABLE "public.t1"
pg_restore: creating TABLE "public.t1_p1"
pg_restore: INFO:  partition constraint for table "t1_p1" is implied by existing constraints
pg_restore: creating CONSTRAINT "public.t1 t1_pkey"
pg_restore: creating CONSTRAINT "public.t1_p1 t1_p1_pkey"
pg_restore: creating CONSTRAINT "public.t1_p1 t1_p1_pkey1"
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 2920; 2606 16395 CONSTRAINT t1_p1 t1_p1_pkey1 edb
pg_restore: [archiver (db)] could not execute query: ERROR:  multiple primary keys for table "t1_p1" are not allowed
    Command was:
-- For binary upgrade, must preserve pg_class oids
SELECT pg_catalog.binary_upgrade_set_next_index_pg_class_oid('16394'::pg_catalog.oid);

ALTER TABLE ONLY "public"."t1_p1"
    ADD CONSTRAINT "t1_p1_pkey1" PRIMARY KEY ("b");