Flashback transaction query output

Question

Hi there,
Here is my small demo.
C:\Documents and Settings\Aman>net start oracleserviceorcl
The OracleServiceORCL service is starting.............................
The OracleServiceORCL service was started successfully.
C:\Documents and Settings\Aman>sqlplus aman/
SQL*Plus: Release 10.2.0.1.0 - Production on Sun Dec 9 19:38:00 2007
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Enter password:
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> create table a ( a number);
create table a ( a number)
ERROR at line 1:
ORA-00955: name is already used by an existing object
SQL> drop table a purge;
Table dropped.
SQL> create table a ( a number);
Table created.
SQL> insert into a values(1);
1 row created.
SQL> insert into a values(2);
1 row created.
SQL> commit;
Commit complete.
SQL> update a set a=100;
2 rows updated.
SQL> commit;
Commit complete.
SQL> select versions_xid from a
2 versions between scn minvalue and maxvalue;
VERSIONS_XID
0A001100F2010000
0A001100F2010000
04001C00DD010000
04001C00DD010000
SQL> select xid, undo_sql
2 from flashback_transaction_query
3 where xid=hextoraw('0A001100F2010000');
XID
UNDO_SQL
0A001100F2010000
update "AMAN"."A" set "A" = '1' where ROWID = 'AAAM5kAAEAAAAG+AAA';
0A001100F2010000
update "AMAN"."A" set "A" = '2' where ROWID = 'AAAM5kAAEAAAAG+AAB';
0A001100F2010000
What I am not able to get is that I should be seeing 2 rows in the output of flashback transaction query view but I am seeing 3 with in one, there is no undo_sql shown but xid is shown. Can anyone let me know why there is this additional third row available and what does it signify?I assume it to be some what associated with commit that I gave but I amot sure as its just a hunch.Any inputs are highly welcome.
Thanks and best regards,
Aman....

Answer 1

Yes, the transaction starts with your first dml statement.
The BEGIN record in flashback_transaction_query marks the beginning of the transaction. If you order the rows by UNDO_CHANGE# you see that the dml statements are returned in reverse order and the last row is the BEGIN row. The view just displays it to mark the beginning of that transaction.
It is a little bit strange as we can identify a single transaction by the XID column, but maybe that row is used for some other internal processing, I am just guessing.
SQL> create table a ( a number);
Table created.
SQL> insert into a values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select versions_xid from a
  2  versions between scn minvalue and maxvalue;
VERSIONS_XID
0029001B0000450B
SQL> column operation format a10
SQL> column table_name format a10
SQL> set lines 100
SQL> column undo_sql format a20
SQL> select xid, undo_sql, table_name, operation, undo_change# from flashback_transaction_query
  2  where xid=hextoraw('0029001B0000450B')
  3  order by undo_change#;
XID              UNDO_SQL             TABLE_NAME OPERATION  UNDO_CHANGE#
0029001B0000450B delete from "SYS"."A A          INSERT                1
                 " where ROWID = 'AAA
                 w4gAABAAAZHrAAA';
0029001B0000450B                                 BEGIN                 2