gotcha in distributed transactions

while I was just running a query fetching records from remote master db(MASTERDB), connection failed...resulted in PMON trying to clean this transaction every now and then(indicated from alert log).... I had worries my client DB(DEVDB) instance could be terminated,then I found way to resolve it as follows...

AT CLIENT DB(runing query fetching data from master db using dblink)

SQL> show parameter db_name

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_name string DEVDB
SQL> show user
USER is "SYS"
SQL> set line 300
SQL> SELECT LOCAL_TRAN_ID, GLOBAL_TRAN_ID, STATE, MIXED, HOST, COMMIT#
2 FROM DBA_2PC_PENDING;

LOCAL_TRAN_ID GLOBAL_TRAN_ID STATE MIX
---------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------------- ---
HOST COMMIT#
-------------------------------------------------------------------------------------------------------------------------------- ----------------
5.6.717654 DEVDB.schemaname.ORG.6c69aa83.5.6.717654 collecting no
schemaname\DEVNODE 3486961816


SQL> set line 80
SQL> desc dba_2pc_pending
Name Null? Type
----------------------------------------- -------- ----------------------------
LOCAL_TRAN_ID NOT NULL VARCHAR2(22)
GLOBAL_TRAN_ID VARCHAR2(169)
STATE NOT NULL VARCHAR2(16)
MIXED VARCHAR2(3)
ADVICE VARCHAR2(1)
TRAN_COMMENT VARCHAR2(255)
FAIL_TIME NOT NULL DATE
FORCE_TIME DATE
RETRY_TIME NOT NULL DATE
OS_USER VARCHAR2(64)
OS_TERMINAL VARCHAR2(255)
HOST VARCHAR2(128)
DB_USER VARCHAR2(30)
COMMIT# VARCHAR2(16)

SQL> col global_tran_id format a35
SQL> /

LOCAL_TRAN_ID GLOBAL_TRAN_ID STATE MIX
---------------------- ----------------------------------- ---------------- ---
HOST
--------------------------------------------------------------------------------
COMMIT#
----------------
5.6.717654 DEVDB.schemaname.ORG.6c69aa83.5.6.717654 collecting no
schemaname\DEVNODE
3486961816


SQL> set line 300
SQL> /

LOCAL_TRAN_ID GLOBAL_TRAN_ID STATE MIX HOST COMMIT#
---------------------- ----------------------------------- ---------------- --- -------------------------------------------------------------------------------------------------------------------------------- ----------------
5.6.717654 DEVDB.schemaname.ORG.6c69aa83.5.6.717654 collecting no schemaname\DEVNODE 3486961816

SQL>
SQL> SELECT LOCAL_TRAN_ID, IN_OUT, DATABASE, INTERFACE
2 FROM DBA_2PC_NEIGHBORS;

LOCAL_TRAN_ID IN_ DATABASE I
---------------------- --- -------------------------------------------------------------------------------------------------------------------------------- -
5.6.717654 in N
5.6.717654 out MASTERDB.schemaname.ORG N

SQL> execute DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY('5.6.717654');
BEGIN DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY('5.6.717654'); END;

*
ERROR at line 1:
ORA-30019: Illegal rollback Segment operation in Automatic Undo mode
ORA-06512: at "SYS.DBMS_TRANSACTION", line 65
ORA-06512: at "SYS.DBMS_TRANSACTION", line 85
ORA-06512: at line 1


SQL> set transaction use rollback segment system
2 ;
set transaction use rollback segment system
*
ERROR at line 1:
ORA-30019: Illegal rollback Segment operation in Automatic Undo mode


SQL> show user;
USER is "SYS"
SQL> alter session set "_smu_debug_mode" = 4;

Session altered.

SQL> execute DBMS_TRANSACTION.PURGE_LOST_DB_ENTRY('5.6.717654');

PL/SQL procedure successfully completed.

SQL> commit;

Commit complete.

SQL> spool off