I think you might have misunderstood what I meant - I was talking about the index insertion case, to verify uniqueness. And that indeed checks the heap regardle

I think you might have misunderstood what I meant - I was talking about the index insertion case, to verify uniqueness. And that indeed checks the heap regardless of the VM bit. Check _bt_doinsert() invocation of _bt_check_unique() and the latter's content. Therefore there's no fundamental problem with having to do the same in hash insertion cases, even if more heap fetches are likely to be necessary. https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/nbtree/nbtinsert.c;h=bf963fcdef22252f79b10ae6f1280ce42ef630a5;hb=HEAD#l240 https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f...