Identify blocked objects and users related, based at http://sushantadba.blogspot.com/2016/05/find-current-and-historical-blocking.html

ORACLE 11g blocking session

select distinct
    b.username user_
    ,d.username blocked_by_user_
    ,t1.time_ 
    ,t1.sql_text
    ,t1.*
from (
    SELECT  distinct a.sql_id, a.blocking_session,a.blocking_session_serial# blocking_session_serial, 
            to_char(a.sample_time,'hh24:mi:ss') time_,
            a.user_id, s.sql_text,a.module
    FROM  V$ACTIVE_SESSION_HISTORY a, v$sql s
        where a.sql_id=s.sql_id
        and blocking_session is not null
        --and a.user_id <> 0
        and a.sample_time between to_date('09/12/2020 00:00', 'dd/mm/yyyy hh24:mi') and to_date('09/12/2020 23:59', 'dd/mm/yyyy hh24:mi')
    )t1
left join ALL_USERS b on (t1.user_id = b.user_id)
left join V$ACTIVE_SESSION_HISTORY c on (t1.blocking_session = c.session_id and t1.blocking_session_serial= c.session_serial#)
left join ALL_USERS d on (c.user_id = d.user_id)
order by 3 desc;