Saturday, April 16, 2011

Flashback_Scn and flashback_Time parameter of Data Pump

Flashback_Scn  and  flashback_Time  are  two  important  feature  of  the  datapump 11g . If  we  want  to  run  a  large  export  whilst  the  database  is  in  use  then  ideally  we  should  always use  one  of  the  two  flashback  parameters. The export  operation  is  performed  with  data  that is  consistent  as  of  the  specified  SCN .  FLASHBACK_SCN and FLASHBACK_TIME are mutually exclusive .

FLASHBACK_TIME : The SCN that most closely matches the specified time is found, and this SCN is used to enable the Flashback utility. The export operation is performed with data that is consistent as of this SCN. The FLASHBACK_SCN parameter pertains only to the Flashback Query capability of Oracle Database. It is not applicable to Flashback Database, Flashback Drop, or Flashback Data Archive. We can get the scn number from the following query :

SQL> select current_scn from v$database ;       or
SQL>select dbms_flashback.get_system_change_number from dual ; 

Let's have a Demo of the flashback_scn

SQL> select current_scn from v$database;
CURRENT_SCN
-----------
    1140271

SQL> create table hr.test as select * from test;
Table created.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
    1140487
Let's take a export using flashback_scn  parameter

C:\>expdp system/ramtech@noida directory=dpump schemas=hr dumpfile=flashback_hr.dmp logfile=flashlog.log       flashback_scn=1140271
Export: Release 11.1.0.6.0 - Production on Saturday, 16 April, 2011 11:35:45
Copyright (c) 2003, 2007, Oracle.  All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_SCHEMA_01":  system/********@noida directory=dpump schemas=hr dumpfile=flashback_hr.dmp logfile=flashlog.log    flashback_scn=1140271
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 512 KB
Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/SEQUENCE/SEQUENCE
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type SCHEMA_EXPORT/TABLE/COMMENT
Processing object type SCHEMA_EXPORT/PROCEDURE/PROCEDURE
Processing object type SCHEMA_EXPORT/PROCEDURE/ALTER_PROCEDURE
Processing object type SCHEMA_EXPORT/VIEW/VIEW
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/REF_CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/TRIGGER
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Processing object type SCHEMA_EXPORT/POST_SCHEMA/PROCACT_SCHEMA
. . exported "HR"."COUNTRIES"                            6.375 KB      25 rows
. . exported "HR"."DEPARTMENTS"                          7.015 KB      27 rows
. . exported "HR"."EMPLOYEES"                            16.80 KB     107 rows
. . exported "HR"."JOBS"                                 6.984 KB      19 rows
. . exported "HR"."JOB_HISTORY"                          7.054 KB      10 rows
. . exported "HR"."LOCATIONS"                            8.273 KB      23 rows
. . exported "HR"."REGIONS"                              5.484 KB       4 rows
ORA-31693: Table data object "HR"."TEST" failed to load/unload and is being skipped due to error:
ORA-02354: error in exporting/importing data
ORA-01466: unable to read data - table definition has changed
Master table "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_01 is:
  D:\DPUMP\FLASHBACK_HR.DMP
Job "SYSTEM"."SYS_EXPORT_SCHEMA_01" completed with 1 error(s) at 11:37:50

The above error show that the table "test"  is not include in the  export operation because the SCN mention  is of before the table "test" creation. The below export will show the export upto current SCN when database is in use.

C:\>expdp system/ramtech@noida directory=dpump schemas=hr dumpfile=flashback_hr1.dmp  logfile=flashback_log.log
Export: Release 11.1.0.6.0 - Production on Saturday, 16 April, 2011 11:44:50
Copyright (c) 2003, 2007, Oracle.  All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_SCHEMA_01":  system/********@noida directory=dpump schemas=hr dumpfile=flashback_hr1.dmp logfile=flashback_log.log
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 512 KB
Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/SEQUENCE/SEQUENCE
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type SCHEMA_EXPORT/TABLE/COMMENT
Processing object type SCHEMA_EXPORT/PROCEDURE/PROCEDURE
Processing object type SCHEMA_EXPORT/PROCEDURE/ALTER_PROCEDURE
Processing object type SCHEMA_EXPORT/VIEW/VIEW
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/REF_CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/TRIGGER
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Processing object type SCHEMA_EXPORT/POST_SCHEMA/PROCACT_SCHEMA
. . exported "HR"."COUNTRIES"                                6.375 KB      25 rows
. . exported "HR"."DEPARTMENTS"                          7.015 KB      27 rows
. . exported "HR"."EMPLOYEES"                             16.80 KB     107 rows
. . exported "HR"."JOBS"                                             6.984 KB      19 rows
. . exported "HR"."JOB_HISTORY"                             7.054 KB      10 rows
. . exported "HR"."LOCATIONS"                                8.273 KB      23 rows
. . exported "HR"."REGIONS"                                      5.484 KB       4 rows
. . exported "HR"."TEST"                                              5.054 KB       8 rows
Master table "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_01 is:
  D:\DPUMP\FLASHBACK_HR1.DMP
Job "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully completed at 11:46:41


Enjoy     :-)



3 comments:

Shailesh Singh said...

Sir during the second attempt for export, you have not mentioned the parameter FLASHBACK_SCN...is that not required

Anonymous said...

By not using the FLASHBACK_SCN you now have an inconsistent export. You will have problems with this export dump when you go to import it. This may be a workaround but it is not a solution.

NEERAJ VISHEN said...

Thnks Shailesh for correcting me ...

Have good time ahead :)