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21 February, 2015

Database Flashback -- 5

Continuing my series on Database Flashback.

Here I demonstrate that Flashback Logs alone are not sufficient.  The process of FLASHBACK DATABASE does need *some* redo entries from Archive/Online Redo Logs.



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

SQL*Plus: Release 11.2.0.2.0 Production on Fri Feb 20 23:18:37 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
---------
20-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       78561280                415383552

SYS>

My database seems to have adequate Flashback Capability in the Flashback Logs.  Let me run some transactions and generate Redo and Flashback.

SYS>connect hemant/hemant
Connected.
HEMANT>drop table obj_list;
drop table obj_list
           *
ERROR at line 1:
ORA-00942: table or view does not exist


HEMANT>create table obj_list tablespace users
  2  as select * from dba_objects where 1=2;

Table created.

HEMANT>select tablespace_name 
  2  from user_tables
  3  where table_name = 'OBJ_LIST';

TABLESPACE_NAME
------------------------------
USERS

HEMANT>insert into obj_list
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects;

225138 rows created.

HEMANT>rollback;

Rollback complete.

HEMANT>insert into obj_list
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects;

225135 rows created.

HEMANT>delete obj_list;

225135 rows deleted.

HEMANT>
HEMANT>select count(*)
  2  from v$archived_log
  3  where first_time > 
  4  (select startup_time
  5   from v$instance)
  6  /

  COUNT(*)
----------
         2

HEMANT>
HEMANT>alter system switch logfile;

System altered.

HEMANT>insert into obj_list
  2  select * from dba_objects
  3  union all
  4  select * from dba_objects
  5  union all
  6  select * from dba_objects
  7  union all
  8  select * from dba_objects;

300180 rows created.

HEMANT>insert into obj_list
  2  select * from obj_list;

300180 rows created.

HEMANT>select count(*) from obj_list;

  COUNT(*)
----------
    600360

HEMANT>commit;

Commit complete.

HEMANT>select count(*) from v$archived_log
  2  where first_time >
  3  (select startup_time from v$instance)
  4  /

  COUNT(*)
----------
         4

HEMANT>

Now, let's suppose that a scheduled (periodic) archive log backup job kicks in and creates a backup of archivelogs and deletes them.

HEMANT>exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@localhost ~]$ rman target /

Recovery Manager: Release 11.2.0.2.0 - Production on Fri Feb 20 23:30:36 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: ORCL (DBID=1229390655)

RMAN> backup as compressed backupset archivelog all delete input;

Starting backup at 20-FEB-15
current log archived
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=58 device type=DISK
channel ORA_DISK_1: starting compressed archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=3 RECID=106 STAMP=872033779
channel ORA_DISK_1: starting piece 1 at 20-FEB-15
channel ORA_DISK_1: finished piece 1 at 20-FEB-15
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnshxs_.bkp tag=TAG20150220T233055 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:04
channel ORA_DISK_1: deleting archived log(s)
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_18/o1_mf_1_3_bg9dcl3v_.arc RECID=106 STAMP=872033779
channel ORA_DISK_1: starting compressed archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=3 RECID=112 STAMP=872205844
input archived log thread=1 sequence=4 RECID=113 STAMP=872205859
input archived log thread=1 sequence=5 RECID=114 STAMP=872205867
input archived log thread=1 sequence=6 RECID=115 STAMP=872206048
input archived log thread=1 sequence=7 RECID=116 STAMP=872206098
input archived log thread=1 sequence=8 RECID=117 STAMP=872206254
channel ORA_DISK_1: starting piece 1 at 20-FEB-15
channel ORA_DISK_1: finished piece 1 at 20-FEB-15
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnsmgc_.bkp tag=TAG20150220T233055 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:15
channel ORA_DISK_1: deleting archived log(s)
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_3_bggndmz4_.arc RECID=112 STAMP=872205844
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_4_bggnf0qy_.arc RECID=113 STAMP=872205859
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_5_bggnf8ty_.arc RECID=114 STAMP=872205867
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_6_bggnlzvr_.arc RECID=115 STAMP=872206048
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_7_bggnnk6c_.arc RECID=116 STAMP=872206098
archived log file name=/home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_8_bggnsg5k_.arc RECID=117 STAMP=872206254
Finished backup at 20-FEB-15

Starting Control File and SPFILE Autobackup at 20-FEB-15
piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/autobackup/2015_02_20/o1_mf_s_872206274_bggnt34k_.bkp comment=NONE
Finished Control File and SPFILE Autobackup at 20-FEB-15

RMAN> exit


Recovery Manager complete.
[oracle@localhost ~]$ 

Now, suppose that I need to Flashback the database.

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

SQL*Plus: Release 11.2.0.2.0 Production on Fri Feb 20 23:32:36 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 * from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FL RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- --------- ---------------- -------------- ------------------------
            14577571 19-FEB-15             1440      135348224               3784998912

SYS>select to_char(oldest_flashback_time,'DD-MON HH24:MI:SS')     
  2  from V$flashback_database_log;

TO_CHAR(OLDEST_FLASHBACK
------------------------
19-FEB 00:04:02

SYS>

Notice how the OLDEST_FLASHBACK_TIME has changed from 17-Feb to the midnight of 18/19-Feb ! Apparently, my FRA cannot hold very many Flashback Logs.
As I have mentioned in two posts earlier, here and here, the scope of the actual ability to Flashback may vary.

Can I flashback to SCN 14577572 ?  Let me give it a try.

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>flashback database to SCN 14577572;
flashback database to SCN 14577572
*
ERROR at line 1:
ORA-38754: FLASHBACK DATABASE not started; required redo log is not available
ORA-38762: redo logs needed for SCN 14577571 to SCN 14577572
ORA-38761: redo log sequence 1 in thread 1, incarnation 5 could not be accessed


SYS>

Aaha ! Apparently, Oracle needs to read some redo from Archive Log(s) !  So, having Flashback Logs alone is *not* sufficient.  I know that I need the database to be running in ArchiveLog mode.  But I should also know that if I want to Flashback to a particular Time or SCN, I will need the corresponding ArchiveLog as well !  (Imaging trying to Flashback to 3 days ago and having purged all ArchiveLogs simply because I do daily Full Backups and have Retention of 2 days only !)

So, I must take the necessary action now.

SYS>!sh
sh-3.2$ rman target /

Recovery Manager: Release 11.2.0.2.0 - Production on Fri Feb 20 23:43:43 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: ORCL (DBID=1229390655, not open)

RMAN> restore archivelog from sequence 1 until sequence 2;

Starting restore at 20-FEB-15
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=21 device type=DISK

channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=1
channel ORA_DISK_1: reading from backup piece /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_19/o1_mf_annnn_TAG20150219T001619_bg9gpq87_.bkp
channel ORA_DISK_1: piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_19/o1_mf_annnn_TAG20150219T001619_bg9gpq87_.bkp tag=TAG20150219T001619
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=2
channel ORA_DISK_1: reading from backup piece /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_19/o1_mf_annnn_TAG20150219T001930_bg9gwl9w_.bkp
channel ORA_DISK_1: piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_19/o1_mf_annnn_TAG20150219T001930_bg9gwl9w_.bkp tag=TAG20150219T001930
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
Finished restore at 20-FEB-15

RMAN> exit


Recovery Manager complete.
sh-3.2$ 
sh-3.2$ exit
exit

SYS>l
  1* flashback database to SCN 14577572
SYS>/

Flashback complete.

SYS>alter database open read only;

Database altered.

SYS>

What if I want to Flashback to another, later time ?

SYS>select sequence#, first_change#, to_char(first_time,'DD-MON HH24:MI:SS')
  2  from v$archived_log
  3  where first_time > trunc(sysdate)
  4  order by 1;

 SEQUENCE# FIRST_CHANGE# TO_CHAR(FIRST_TIME,'DD-M
---------- ------------- ------------------------
         4      14580736 20-FEB 23:24:03
         5      14581651 20-FEB 23:24:16
         6      14583536 20-FEB 23:24:23
         7      14584203 20-FEB 23:27:27
         8      14584351 20-FEB 23:28:17

SYS>
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>flashback database to SCN 14584205;
flashback database to SCN 14584205
*
ERROR at line 1:
ORA-38754: FLASHBACK DATABASE not started; required redo log is not available
ORA-38762: redo logs needed for SCN 14577573 to SCN 14584205
ORA-38761: redo log sequence 5 in thread 1, incarnation 5 could not be accessed


SYS>
SYS>!sh
sh-3.2$ rman target /

Recovery Manager: Release 11.2.0.2.0 - Production on Fri Feb 20 23:53:48 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: ORCL (DBID=1229390655, not open)

RMAN> restore archivelog from sequence 5 until sequence 6;

Starting restore at 20-FEB-15
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=21 device type=DISK

channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=5
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=6
channel ORA_DISK_1: reading from backup piece /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnsmgc_.bkp
channel ORA_DISK_1: piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnsmgc_.bkp tag=TAG20150220T233055
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:15
Finished restore at 20-FEB-15

RMAN> exit


Recovery Manager complete.
sh-3.2$ 
sh-3.2$ cd /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20
sh-3.2$ ls -l 
total 63344
-rw-rw---- 1 oracle oracle   494592 Feb 20 23:44 o1_mf_1_1_bggol5t8_.arc
-rw-rw---- 1 oracle oracle    18432 Feb 20 23:44 o1_mf_1_2_bggol6wm_.arc
-rw-rw---- 1 oracle oracle 50630144 Feb 20 23:54 o1_mf_1_5_bggp4zbp_.arc
-rw-rw---- 1 oracle oracle 13635072 Feb 20 23:54 o1_mf_1_6_bggp4zh3_.arc
sh-3.2$ 

I have Sequences 1 and 2 that were restored for the first flashback and Sequences 5 and 6 that have been restored now. Do I need Sequences 3 and 4 ? Do I need Sequence 7 (that contains the Redo beyond SCN 14584203) ?

Let's see.
sh-3.2$ exit
exit

SYS>l
  1* flashback database to SCN 14584205
SYS>/
flashback database to SCN 14584205
*
ERROR at line 1:
ORA-38754: FLASHBACK DATABASE not started; required redo log is not available
ORA-38762: redo logs needed for SCN 14577573 to SCN 14584205
ORA-38761: redo log sequence 3 in thread 1, incarnation 5 could not be accessed


SYS>
Apparently, I also need Sequences 3,at least,  and (maybe ?) 4 ! Why ? Because my database is currently at an SCN lower than the one I want to Flashback to and the corresponding redo is required. (If I had *not* done the first Flashback to the lower SCN, I wouldn't need these Archivelogs !)

SYS>!sh
sh-3.2$ rman target /

Recovery Manager: Release 11.2.0.2.0 - Production on Sat Feb 21 00:01:34 2015

Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.

connected to target database: ORCL (DBID=1229390655, not open)

RMAN> restore archivelog from sequence 3 until sequence 4;

Starting restore at 21-FEB-15
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=17 device type=DISK

channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=3
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=4
channel ORA_DISK_1: reading from backup piece /home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnsmgc_.bkp
channel ORA_DISK_1: piece handle=/home/oracle/app/oracle/flash_recovery_area/ORCL/backupset/2015_02_20/o1_mf_annnn_TAG20150220T233055_bggnsmgc_.bkp tag=TAG20150220T233055
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:15
Finished restore at 21-FEB-15

RMAN> exit


Recovery Manager complete.
sh-3.2$ 
sh-3.2$ cd /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20
sh-3.2$ ls -l
total 63344
-rw-rw---- 1 oracle oracle   494592 Feb 20 23:44 o1_mf_1_1_bggol5t8_.arc
-rw-rw---- 1 oracle oracle    18432 Feb 20 23:44 o1_mf_1_2_bggol6wm_.arc
-rw-rw---- 1 oracle oracle 50630144 Feb 20 23:54 o1_mf_1_5_bggp4zbp_.arc
-rw-rw---- 1 oracle oracle 13635072 Feb 20 23:54 o1_mf_1_6_bggp4zh3_.arc
sh-3.2$ cd ../*21
sh-3.2$ ls -l
total 80272
-rw-rw---- 1 oracle oracle 31472640 Feb 21 00:01 o1_mf_1_3_bggpmf06_.arc
-rw-rw---- 1 oracle oracle 50630144 Feb 21 00:01 o1_mf_1_4_bggpmdxk_.arc
sh-3.2$ 

Here is something important (nothing to do with Flashback Database).  The server clock went past midnight into 21-Feb so the restored files went into 2015_02_21 and not 2015_02_20 !

sh-3.2$ exit
exit

SYS>l
  1* flashback database to SCN 14584205
SYS>/

Flashback complete.

SYS>

Remember my question about whether I would need Sequence 7 ?  Let's see what the alert.log shows about the Flashback Database actions.

Flashback Media Recovery Log /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_2_bggol6wm_.arc
Flashback Media Recovery Log /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_21/o1_mf_1_3_bggpmf06_.arc
Flashback Media Recovery Log /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_21/o1_mf_1_4_bggpmdxk_.arc
Flashback Media Recovery Log /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_5_bggp4zbp_.arc
Flashback Media Recovery Log /home/oracle/app/oracle/flash_recovery_area/ORCL/archivelog/2015_02_20/o1_mf_1_6_bggp4zh3_.arc
Recovery of Online Redo Log: Thread 1 Group 1 Seq 7 Reading mem 0
  Mem# 0: /home/oracle/app/oracle/oradata/orcl/redo01.log
Incomplete Recovery applied until change 14584206 time 02/20/2015 23:28:03
Flashback Media Recovery Complete
Completed: flashback database to SCN 14584205

Another learning point !  Sequence 7 was applied from the Online Redo Log file.

What we have learned :
1.  If we Flashback the database to a particular SCN / Time / Restore Point, Oracle does need the Redo from the Archive / Online Redo Log file that was active at that time.  It still needs some Redo to make the database consistent (e.g. apply Undo)

2. If we Flashback the database to SCN 101 and then (without OPEN RESETLOGS), choose to Flashback to a subsequent SCN 201, we again need ArchiveLogs !

3. Flashback from the SQL command-line is intelligent enough to use the Online Redo Log but not (like, say, RMAN's RECOVER DATABASE), automatically restore ArchiveLogs as they are required !

.
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