Here’s how to find out which session is waiting for a shared resource to be released:

Column host     format a6;Column username format a10;Column os_user  format a8;Column program  format a30;Column tsname   format a12; select   b.machine         host,   b.username        username,   b.server,   b.osuser          os_user,   b.program         program,   a.tablespace_name ts_name,   row_wait_file#    file_nbr,   row_wait_block#   block_nbr,   c.owner,   c.segment_name,   c.segment_typefrom   dba_data_files a,   v$session      b,   dba_extents    cwhere   b.row_wait_file# = a.file_idand   c.file_id = row_wait_file#and  row_wait_block#  between c.block_id and c.block_id + c.blocks - 1and  row_wait_file# <> 0and  type='USER';

The returned username will tell you the name of the user account waiting for a lock to be released at a block number.