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17 February, 2015

Database Flashback -- 4

Continuing my series on Oracle Database Flashback.  This post demonstrates a FLASHBACK DATABASE when a Tablespace is set to  FLASHBACK OFF.

UPDATE 20-Feb-15 : When might I have FLASHBACK OFF for a Tablespace in a FLASHBACK ON Database ?  When, the Tablespace contents are "throwaway-able".  I can avoid the overheads of Flashback for DML in the Tablespace and I am confident that on the rare occasion that I have to Flashback the Database, I can discard and rebuild the tablespace and it's contents because they are not important for persistency.


[oracle@localhost Hemant]$ sqlplus '/ as sysdba'

SQL*Plus: Release 11.2.0.2.0 Production on Tue Feb 17 22:30:53 2015

Copyright (c) 1982, 2010, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SYS>select sysdate from dual;

SYSDATE
---------
17-FEB-15

SYS>show parameter db_flashback_retention_target

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target        integer     1440
SYS>select * from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FL RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- --------- ---------------- -------------- ------------------------
            14573520 15-FEB-15             1440      190971904                        0

SYS>

After my last post on 15/16-Feb (midnight), I had generated some transactions. The Flashback Size has grown from 24.576MB to 190.972MB.

Question : Does Database Flashback always apply to the whole database ?  Can we exclude a selected tablespace ?

SYS>create tablespace TEST_NOFB;

Tablespace created.

SYS>alter tablespace TEST_NOFB flashback OFF;

Tablespace altered.

SYS>

So, it is possible to set FLASHBACK OFF for a tablespace !  What are the implications ?  Oracle does NOT save Flashback information for this tablespace.  If I need to Flashback the Database, this tablespace or all the datafiles in this tablespace must be taken OFFLINE or DROPped.

UPDATE : 18-FEB-15

Continuing the case.
Note : Subsequent to last night's post I had some more activity on the database and even a RESTORE and RESETLOGS.  The v$flashback_database_log contents are different now.

[oracle@localhost Hemant]$ sqlplus '/ as sysdba'

SQL*Plus: Release 11.2.0.2.0 Production on Wed Feb 18 23:27:19 2015

Copyright (c) 1982, 2010, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SYS>select sysdate from dual;

SYSDATE
---------
18-FEB-15

SYS>show parameter db_flashback_retention_target

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target        integer     1440
SYS>select * from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FL RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- --------- ---------------- -------------- ------------------------
            14573526 17-FEB-15             1440       62783488                        0

SYS>

Now, let me create a RESTORE POINT and then some activity in the TEST_NOFB database.

SYS>create restore point FEB18_15;

Restore point created.

SYS>connect hemant/hemant
Connected.
HEMANT>create table test_nofb_tbl tablespace test_nofb
  2  as select * from dba_objects
  3  where 1=2;

Table created.

HEMANT>select tablespace_name 
  2  from user_tables
  3  where table_name = 'TEST_NOFB_TBL'
  4  /

TABLESPACE_NAME
------------------------------
TEST_NOFB

HEMANT>insert into test_nofb_tbl
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects
  7  /

225138 rows created.

HEMANT>truncate table test_nofb_tbl;

Table truncated.

HEMANT>insert into test_nofb_tbl
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects
  7  /

225138 rows created.

HEMANT>commit;

Commit complete.

HEMANT>connect / as sysdba
Connected.
SYS>select * from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FL RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- --------- ---------------- -------------- ------------------------
            14573526 17-FEB-15             1440       62783488                646397952

SYS>

So, I have generated DML activity in the TEST_NOFB Tablespace.

Let me define another Restore Point and generate more DML.

SYS>create restore point FEB18_15_2nd;

Restore point created.

SYS>connect hemant/hemant
Connected.
HEMANT>insert into test_nofb_tbl
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects
  7  /

225138 rows created.

HEMANT>commit;

Commit complete.

HEMANT>select count(*) from test_nofb_tbl;

  COUNT(*)
----------
    450276

HEMANT>

I now have two Restore Points and DML against the target table in a FLASHBACK OFF Tablespace between and after the Restore Points.

Let my try to Flashback to the 2nd Restore Point.  What should I see ?  225138 rows in the table ? Or no rows in the table ?

HEMANT>connect / as sysdba
Connected.
SYS>shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS>startup mount
ORACLE instance started.

Total System Global Area  456146944 bytes
Fixed Size                  1344840 bytes
Variable Size             394267320 bytes
Database Buffers           54525952 bytes
Redo Buffers                6008832 bytes
Database mounted.
SYS>
SYS>flashback database to restore point FEB18_15_2nd;
flashback database to restore point FEB18_15_2nd
*
ERROR at line 1:
ORA-38753: Cannot flashback data file 6; no flashback log data.
ORA-01110: data file 6: '/home/oracle/app/oracle/oradata/orcl/ORCL/datafile/o1_mf_test_nof_bg9cq9bv_.dbf'


SYS>

AAHA ! It cannot flashback the datafile because no flashback log exists for it.

Let me quote again what I said yesterday :  If I need to Flashback the Database, this tablespace or all the datafiles in this tablespace must be taken OFFLINE or DROPped.

So, I must take the necessary action :

SYS>alter database datafile 6 offline;

Database altered.

SYS>flashback database to restore point FEB18_15_2nd;

Flashback complete.

SYS>alter database open read only;

Database altered.

SYS>
SYS>alter database datafile 6 online;
alter database datafile 6 online
*
ERROR at line 1:
ORA-01113: file 6 needs media recovery
ORA-01110: data file 6: '/home/oracle/app/oracle/oradata/orcl/ORCL/datafile/o1_mf_test_nof_bg9cq9bv_.dbf'


SYS>recover datafile 6;
ORA-00283: recovery session canceled due to errors
ORA-38798: Cannot perform partial database recovery
ORA-38797: Full database recovery required after a database has been flashed back


SYS>

I *cannot* selectively recover that datafile.  What options do I have ?
In the meantime, let's look at the alert.log.

Wed Feb 18 23:47:04 2015
flashback database to restore point FEB18_15_2nd
ORA-38753 signalled during: flashback database to restore point FEB18_15_2nd...
Wed Feb 18 23:49:42 2015
alter database datafile 6 offline
Completed: alter database datafile 6 offline
flashback database to restore point FEB18_15_2nd
Flashback Restore Start
Flashback Restore Complete
Flashback Media Recovery Start
Serial Media Recovery started
Warning: Datafile 6 (/home/oracle/app/oracle/oradata/orcl/ORCL/datafile/o1_mf_test_nof_bg9cq9bv_.dbf) is offline during full database recovery and will not be recovered
Recovery of Online Redo Log: Thread 1 Group 3 Seq 3 Reading mem 0
  Mem# 0: /home/oracle/app/oracle/oradata/orcl/redo03.log
Recovery of Online Redo Log: Thread 1 Group 1 Seq 4 Reading mem 0
  Mem# 0: /home/oracle/app/oracle/oradata/orcl/redo01.log
Incomplete Recovery applied until change 14577570 time 02/18/2015 23:40:29
Flashback Media Recovery Complete
Completed: flashback database to restore point FEB18_15_2nd
Wed Feb 18 23:50:08 2015
alter database open read only
AUDIT_TRAIL initialization parameter is changed to OS, as DB is NOT compatible for database opened with read-only access
ARCH: STARTING ARCH PROCESSES
.....
.....
Completed: alter database open read only
Wed Feb 18 23:50:10 2015
.....
.....
Wed Feb 18 23:50:36 2015
alter database datafile 6 online
ORA-1113 signalled during: alter database datafile 6 online...
Wed Feb 18 23:50:36 2015
Signalling error 1152 for datafile 6!
Checker run found 2 new persistent data failures
ALTER DATABASE RECOVER  datafile 6
Media Recovery Start
Serial Media Recovery started
Media Recovery failed with error 38798
ORA-283 signalled during: ALTER DATABASE RECOVER  datafile 6  ...

So, the datafile is unusable.
I can only drop the tablespace.

SYS>shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS>startup mount;
ORACLE instance started.

Total System Global Area  456146944 bytes
Fixed Size                  1344840 bytes
Variable Size             394267320 bytes
Database Buffers           54525952 bytes
Redo Buffers                6008832 bytes
Database mounted.
SYS>
SYS>recover datafile 6;
ORA-00283: recovery session canceled due to errors
ORA-38798: Cannot perform partial database recovery
ORA-38797: Full database recovery required after a database has been flashed back


SYS>alter database open;
alter database open
*
ERROR at line 1:
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open


SYS>alter database open resetlogs;

Database altered.

SYS>
SYS>recover datafile 6;
ORA-00283: recovery session canceled due to errors
ORA-19909: datafile 6 belongs to an orphan incarnation
ORA-01110: data file 6: '/home/oracle/app/oracle/oradata/orcl/ORCL/datafile/o1_mf_test_nof_bg9cq9bv_.dbf'


SYS>select tablespace_name from dba_data_files
  2  where file_id=6;

TABLESPACE_NAME
------------------------------
TEST_NOFB

SYS>drop tablespace test_nofb;
drop tablespace test_nofb
*
ERROR at line 1:
ORA-01549: tablespace not empty, use INCLUDING CONTENTS option


SYS>drop tablespace test_nofb including contents and datafiles;

Tablespace dropped.

SYS>

There ! A Tablespace that was in FLASHBACK OFF mode cannot be accessed after a Flashback Database --- not even in respect to data that existed before the Restore Point that is used for the Flashback.
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