UPSERT on partition

Hi,

INSERT ON CONFLICT DO UPDATE doesn't seem to work on the current partitioning
mechanism. For example, in the following SQL commands, the last UPSERT command
would fail with an error. The error message is

ERROR: duplicate key value violates unique constraint "hoge_20150601_pkey"
DETAIL: Key (col1)=(2015-06-01 10:30:00) already exists.
CONTEXT: SQL statement "INSERT INTO hoge_20150601 VALUES (($1).*)"
PL/pgSQL function hoge_insert_trigger() line 6 at EXECUTE statement

------------------------------------------------------------------------------------
CREATE TABLE hoge (col1 TIMESTAMP PRIMARY KEY, col2 INT);

CREATE OR REPLACE FUNCTION hoge_insert_trigger () RETURNS trigger AS
$$
DECLARE
part TEXT;
BEGIN
part := 'hoge_' || to_char(new.col1,
'YYYYMMDD');
EXECUTE 'INSERT INTO ' || part || '
VALUES (($1).*)' USING new;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;

CREATE TRIGGER insert_hoge_trigger
BEFORE INSERT ON hoge
FOR EACH ROW EXECUTE PROCEDURE hoge_insert_trigger();

CREATE TABLE hoge_20150601 (
LIKE hoge INCLUDING INDEXES
INCLUDING DEFAULTS
INCLUDING CONSTRAINTS,
CHECK ('2015-06-01 00:00:00' <= col1 AND col1 < '2015-06-02 00:00:00')
)
INHERITS (hoge);

CREATE TABLE hoge_20150602 (
LIKE hoge INCLUDING INDEXES
INCLUDING DEFAULTS
INCLUDING CONSTRAINTS,
CHECK ('2015-06-02 00:00:00' <= col1 AND col1 < '2015-06-03 00:00:00')
)
INHERITS (hoge);

INSERT INTO hoge VALUES ('2015-06-01 10:30:00', 1234)
ON CONFLICT (col1) DO UPDATE SET col2 = EXCLUDED.col2;

INSERT INTO hoge VALUES ('2015-06-01 10:30:00', 1234)
ON CONFLICT (col1) DO UPDATE SET col2 = EXCLUDED.col2;
------------------------------------------------------------------------------------

How should we treat this problem for 9.5? If we want to fix this problem
completely, probably we would need to make constraint_exclusion work with
even UPSERT. Which sounds difficult to do at least for 9.5. Any other idea?
Or we should just treat it as a limitation of UPSERT and add that document?

Thought?

Regards,

--
Fujii Masao