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We have the dblink pm from DB2 to DB1

In DB1:


SQL> create table test02049 as select * from user_objects where rownum<3;

Table created.

SQL> select object_name from test02049;

OBJECT_NAME
-----------------------------------------------------------------------------------
ACCOUNT
ACTIVITYCODEHIERARCHY

SQL> 

In DB2:

SQL> select object_name from test02049@pm;

OBJECT_NAME
--------------------------------------------------------------------------------------
ACCOUNT
ACTIVITYCODEHIERARCHY


SQL> -- session one
SQL> update test02049@pm set object_name ='new_obj1' where object_name ='ACCOUNT';

1 row updated.

SQL> 

We did not make the commit nor rollback

open second session on DB2

SQL> -- session two
SQL> update test02049@pm set object_name ='new_obj2'  where object_name ='ACCOUNT';
update test02049@pm set object_name ='new_obj2'  where object_name ='ACCOUNT'
*
ERROR at line 1:
ORA-02049: timeout: distributed transaction waiting for lock
ORA-02063: preceding line from PM

Before the second session got time out. 

In DB1:

SQL> @vlockb

USERNAME          SID   SERIAL# TYPE     CTIME HELD       REQ             ID1      ID2
--------------- ----- --------- ---- --------- ---------- ---------- -------- --------
PRIVUSER         2836      3669 TX          21 Exclusive  None         917504  1325382
PRIVUSER         2881     53329 TX          18 None       Exclusive    917504  1325382

-- we have the blocker 2836, and the requester 2881

SQL> l
  1  SELECT SN.Username, M.Sid, SN.SERIAL#,   M.Type, m.ctime,
  2  DECODE(M.Lmode, 0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row
  3  Excl.', 4, 'Share', 5, 'S/Row Excl.', 6, 'Exclusive',  LTRIM(TO_CHAR(Lmode,'990'))) Lmode,
  4  DECODE(M.Request, 0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row Excl.', 4, 'Share', 5, 'S/Row E
  5  LTRIM(TO_CHAR(M.Request, '990'))) Request,
  6  M.Id1, M.Id2
  7  FROM V$SESSION SN
  8  , V$LOCK M
  9  WHERE
 10  (SN.Sid = M.Sid and M.Request ! = 0)
 11  or (SN.Sid = M.Sid and M.Request = 0 and Lmode != 4 and (id1, id2)
 12  in (select S.Id1, S.Id2 from V$LOCK S where Request != 0 and S.Id1
 13  = M.Id1 and S.Id2 = M.Id2) )
 14* order by Id1, Id2, M.Request

we want to check out the sql by the blocker:

SQL> @showsql
Enter value for sid_or_null: 2836
old   6: and sid = NVL('&sid_or_null',sid)
new   6: and sid = NVL('2836',sid)

no rows selected

-- We found none.

Then check on the requester:

SQL> /
Enter value for sid_or_null: 2881
old   6: and sid = NVL('&sid_or_null',sid)
new   6: and sid = NVL('2881',sid)

USERNAME            SID SQL_TEXT
--------------- ------- ------------------------------------------------------------
PRIVUSER           2881 UPDATE "TEST02049" "A1" SET "OBJECT_NAME" = :"SYS_B_0" WHERE
                         "A1"."OBJECT_NAME"=:"SYS_B_1"


SQL> 
SQL> l
  1  select username, sid, sql_text
  2  from
  3  v$sql sql,
  4  v$session sess
  5  where sql.address = sess.sql_address
  6* and sid = NVL('&sid_or_null',sid)
SQL> 

why we did not see the sql from the blocker?

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