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     :-)



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Friday, April 15, 2011

Estimate Parameter in Data Pump Export

ESTIMATE  parameter  of data pump  export specify the method that Export will use to estimate how much disk space  each  table in the export  job will  consume (in bytes)  before  performing actual data pump export operation .
The ESTIMATE parameter can take two parameters. Either BLOCKS (default) or STATISTICS. The meaning of these two parameter values are specified below.

BLOCKS : The estimate is calculated by multiplying the number of database blocks used by the target objects with the appropriate block sizes.
STATISTICS : The estimate is calculated using statistics for each table. So to be accurate you must analyze table recently.

Note that the outcome specified by ESTIMATE=BLOCKS is far away from the size of the actual dumpfile. In fact, ESTIMATE=BLOCKS method generates more inaccurate result from dump file size when,

a) The table was created with a much bigger initial extent size than was needed for the actual table data.
b) Many rows have been deleted from the table, or a very small percentage of each block is used.
The outcome generated by ESTIMATE=STATISTICS is most accurate to dump file size if recently table is analyzed.

Below is an example shown both in case of ESTIMATE=STATISTICS and ESTIMATE=BLOCKS. In both cases data pump export dump file is generated after estimation of dump file.

C:\>expdp system/ramtech@noida directory=dpump  schemas=hr logfile=hrlog11.log dumpfile=hr.dmp ESTIMATE=BLOCKS
Export: Release 11.1.0.6.0 - Production on Friday, 15 April, 2011 19:26:02
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 logfile=hrlog11.log ESTIMATE=BLOCKS
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
.  estimated "HR"."COUNTRIES"                                64 KB
.  estimated "HR"."DEPARTMENTS"                          64 KB
.  estimated "HR"."EMPLOYEES"                               64 KB
.  estimated "HR"."JOBS"                                             64 KB
.  estimated "HR"."JOB_HISTORY"                             64 KB
.  estimated "HR"."LOCATIONS"                                64 KB
.  estimated "HR"."REGIONS"                                     64 KB
Total estimation using BLOCKS method: 448 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
Master table "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_01 is:
  D:\DPUMP\EXPDAT.DMP
Job "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully completed at 19:28:16

Now we will export the schemas by using ESTIMATE=STATISTICS

C:\>expdp system/ramtech@noida directory=dpump  schemas=hr dumpfile=hr1.dmp logfile=hrlog111.log ESTIMATE=STATISTICS
 Export: Release 11.1.0.6.0 - Production on Friday, 15 April, 2011 19:31:15
 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=hr1.dmp logfile=hrlog111.log ESTIMATE=STATISTICS
Estimate in progress using STATISTICS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
.  estimated "HR"."EMPLOYEES"                           15.91 KB
.  estimated "HR"."LOCATIONS"                             8.034 KB
.  estimated "HR"."JOB_HISTORY"                          6.861 KB
.  estimated "HR"."JOBS"                                           6.795 KB
.  estimated "HR"."DEPARTMENTS"                        6.710 KB
.  estimated "HR"."COUNTRIES"                              6.150 KB
.  estimated "HR"."REGIONS"                                   5.488 KB
Total estimation using STATISTICS method: 55.95 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"."EMPLOYEES"                            16.80 KB     107 rows
. . exported "HR"."LOCATIONS"                            8.273 KB      23 rows
. . exported "HR"."JOB_HISTORY"                          7.054 KB      10 rows
. . exported "HR"."JOBS"                                 6.984 KB      19 rows
. . exported "HR"."DEPARTMENTS"                          7.015 KB      27 rows
. . exported "HR"."COUNTRIES"                            6.375 KB      25 rows
. . exported "HR"."REGIONS"                              5.484 KB       4 rows
Master table "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_01 is:
  D:\DPUMP\HR1.DMP
Job "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully completed at 19:33:24

Using ESTIMATE=BLOCKS, before data pump export size is shown as 448 KB and using ESTIMATE=STATISTICS, before data pump export size is shown as 55.95 KB and my actual dump file size was 408KB which is away from estimation using ESTIMATE=BLOCKS as difference is 448-408=40 KB. In later case difference is 448-55.95=392.05KB

Note that if a table involves LOBs, the dump file size may vary as ESTIMATE does not take LOB size into consideration.

Enjoy      J J J


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How To Estimate Disk Space Needed for an Export Job ?

If we  just  want to  know how  much  disk space  for  the  dump  without  actually   exporting  any data, we  can use the ESTIMATE_ONLY=y parameter on  the  expdp  command. ESTIMATE_ONLY=y  parameter  estimate  the space in bytes per tables. The below demo will show that how a system user wants to see the disk space estimates on  hr and scott schemas export . 

C:\>expdp system/ramtech@noida directory=dpump  schemas=scott,hr estimate_only=y
Export: Release 11.1.0.6.0 - Production on Friday, 15 April, 2011 18:56:03
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=scott,hr logfile=scott_hr.log estimate_only=y
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
.  estimated "HR"."COUNTRIES"                               64 KB
.  estimated "HR"."DEPARTMENTS"                             64 KB
.  estimated "HR"."EMPLOYEES"                               64 KB
.  estimated "HR"."JOBS"                                    64 KB
.  estimated "HR"."JOB_HISTORY"                             64 KB
.  estimated "HR"."LOCATIONS"                               64 KB
.  estimated "HR"."REGIONS"                                 64 KB
.  estimated "SCOTT"."DEPT"                                 64 KB
.  estimated "SCOTT"."EMP"                                  64 KB
.  estimated "SCOTT"."SALGRADE"                             64 KB
.  estimated "SCOTT"."BONUS"                                 0 KB
Total estimation using BLOCKS method: 640 KB
Job "SYSTEM"."SYS_EXPORT_SCHEMA_01" successfully completed at 18:57:38

Now we see that we need 640 KB disk space to export the entire data base.

Note : 

  • The ESTIMATE_ONLY parameter cannot be used in conjunction with the QUERY parameter dumpfile.
  • Estimate Parameter  do not give the accurate size . It gives the approax.  size of the dumpfile . 
  • If the Data Pump export job involves compressed tables, the default size estimation given for the compressed table is inaccurate when ESTIMATE=BLOCKS is used. This is because the size estimate does not reflect that the data was stored in a compressed form. To get a more accurate size estimate for compressed tables, use ESTIMATE=STATISTICS.
  • The estimate may also be inaccurate if the QUERY, SAMPLE, or REMAP_DATA parameter is used.
Enjoy    :-) 



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