postgres=# explain insert into test(id,info,crt_time) values(1, md5(random()::text), now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt_time;
 QUERY PLAN 
------------------------------------------------------------------------
 Insert on test (cost=0.00..0.03 rows=1 width=44)
 Conflict Resolution: UPDATE
 Conflict Arbiter Indexes: test_pkey
 -> Custom Scan (PartitionFilter) (cost=0.00..0.03 rows=1 width=44)
 -> Result (cost=0.00..0.03 rows=1 width=44)
(5 rows)
postgres=# insert into test(id,info,crt_time) values(1, md5(random()::text), now()) on conflict (id) do update set info=excluded.info,crt_time=excluded.crt_time;
ERROR: XX000: unexpected failure to find arbiter index
LOCATION: ExecCheckIndexConstraints, execIndexing.c:594