use these sqls below:
create table t(a int);
insert into t values(1);
select lp,lp_off,lp_len,t_data from heap_page_items(get_raw_page('t',0));
lp | lp_off | lp_len | t_data
----+--------+--------+------------
1 | 8160 | 28 | \x01000000
--------------------------------------------------------------------------------
jacktby@gmail.com