enq:HW contention

If the event is constantly occurring in the database, just run the following query to identify the sessions encountering the HW contention

1.select * from v$session_wait where event='enq: HW - contention';

Determine the correct file and block number

2.select DBMS_UTILITY.DATA_BLOCK_ADDRESS_FILE(51236787) FILE#,
DBMS_UTILITY.DATA_BLOCK_ADDRESS_BLOCK(51236787) BLOCK#

from dual;

FILE#  BLOCK#
12 905139

here you will get file and block no 
in the above query   "51236787" is P3 value from V$session query 1.

Optionally can check file name  by query -

3.select * from dba_data_files where file_id='12';

now get  segment name and owner from query: 

4. select owner, segment_type, segment_name

   from dba_extents

   where file_id = 12

   and 905139 between block_id and block_id + blocks - 1;

Next, isolate the table name that references this LOB segment 

using the following query:

5. select * from all_lobs where segment_name='SYS_LOB0000124825C00354$$';

Determine the biggest extent size of this object for segment space management auto

6. SELECT

    DISTINCT bytes

    FROM dba_extents

   WHERE segment_name = 'SYS_LOB0000124825C00354$$';

    AND owner = 'SCOTT';

Add some extents to this LOB segment:

7. ALTER TABLE SCOTT.EMPLOYEE

   MODIFY LOB (JOININGDOC_BYTE)

              (ALLOCATE EXTENT (SIZE 1M));

check again for this enqueue  by  query 1. Now you wont get it .