RMAN Tablespace Point-in-Time Recovery(TSPIR) in Oracle 11gR2

Recovery Manager (RMAN) Automatic TSPITR enables quick recovery of one or more tablespaces in a database to an earlier time without affecting the rest of the tablespaces and objects in the database.

RMAN TSPITR is most useful for the following situations:

• We want to recover a logical database to a point different from the rest of the physical database, when multiple logical databases exist in separate tablespaces of one physical database. For example, we maintain logical databases in the orders and personnel tablespaces. An incorrect batch job or DML statement corrupts the data in only one of the tablespaces.
• We want to recover data lost after DDL operations that change the structure of tables. We cannot use Flashback Table to rewind a table to before the point of a structural change such as a truncate table operation.
• We want to recover a table after it has been dropped with the PURGE option.
• We want to recover from the logical corruption of a table.
• We want to recover dropped tablespaces. In fact, RMAN can perform TSPITR on dropped tablespaces even when a recovery catalog is not used.
• We can also use Flashback Database to rewind data, but we must rewind the entire database rather than just a subset. Also, unlike TSPITR, the Flashback Database feature necessitates the overhead of maintaining flashback logs. The point in time to which you can flash back the database is more limited than the TSPITR window, which extends back to our earliest recoverable backup.

TSPIR was there in  earleir release but have some limitation i.e, we cannot recover a dropped tablespace .  Oracle 11gr2 performs a fully automated managed  TSPIR. It automatically creates and start the auxiliary instance and restores the datafiles it requires and the files pertaining to the dropped tablespace. It will first 

perform a recovery of the tablespace on the auxiliary instance and then use Data Pump and Transportable Tablespace technology to extract and import the tablespace meta data into the original source database .

Here we will illustrate the Concept of TSPIR with an example .

We will create a user say  "TSPIR"  and assign the default tablespace say "tspir"  and create  tables in this tablespace. We take the full backup of the database and further drop the tablespace "tspir" . Before dropping we we note the scn and use this scn to do TSPIR . Below are steps for the TSPIR

Step 1 :  Clean the previous failed TSPIR 

SQL> exec dbms_backup_restore.manageauxinstance ('TSPITR',1) ;
PL/SQL procedure successfully completed.

Step 2 :  Create tablespace and Users and Create tables

SQL> create tablespace tspir datafile 'C:\app\neerajs\oradata\orcl\tspir.dbf' size 150m autoextend on;
Tablespace created.

SQL> create user tspir identified by tspir
  2  default tablespace tspir
  3  quota unlimited on tspir;
User created.

SQL> grant resource,connect to tspir;
Grant succeeded.

SQL> connect tspir/tspir@orcl
Connected.

SQL> create table test(id number);
Table created.

SQL> insert into test values(12);
1 row created.

SQL> insert into test values(121);
1 row created.

SQL> commit;
Commit complete.

SQL> select * from test;
        ID
----------
        12
       121

SQL> create table emp as select * from user_objects;
Table created.

SQL> select count(*) from emp;
  COUNT(*)
----------
         2

SQL> conn / as sysdba
Connected.

Step  3  :   Take the fresh backup of database 

SQL> host   rman   target   sys@orcl
Recovery Manager: Release 11.2.0.1.0 - Production on Wed Nov 30 14:35:44 2011
Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
target database Password:
connected to target database: ORCL (DBID=1296005542)

RMAN> backup database plus archivelog;
Starting backup at 30-NOV-11
current log archived
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=141 device type=DISK
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=3 RECID=1 STAMP=768238310
input archived log thread=1 sequence=4 RECID=2 STAMP=768238310
input archived log thread=1 sequence=5 RECID=3 STAMP=768238311
input archived log thread=1 sequence=6 RECID=4 STAMP=768238314
input archived log thread=1 sequence=7 RECID=5 STAMP=768239453
input archived log thread=1 sequence=8 RECID=6 STAMP=768239455
input archived log thread=1 sequence=9 RECID=7 STAMP=768305386
input archived log thread=1 sequence=10 RECID=8 STAMP=768334227
input archived log thread=1 sequence=11 RECID=9 STAMP=768393025
input archived log thread=1 sequence=12 RECID=10 STAMP=768454251
input archived log thread=1 sequence=13 RECID=11 STAMP=768521484
input archived log thread=1 sequence=14 RECID=12 STAMP=768580566
channel ORA_DISK_1: starting piece 1 at 30-NOV-11
channel ORA_DISK_1: finished piece 1 at 30-NOV-11
piece handle=F:\RMAN_BKP\01MSV6UP_1_1 tag=TAG20111130T143608 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:55
Finished backup at 30-NOV-11

Starting backup at 30-NOV-11
using channel ORA_DISK_1
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00001 name=C:\APP\NEERAJS\ORADATA\ORCL\SYSTEM01.DBF
input datafile file number=00002 name=C:\APP\NEERAJS\ORADATA\ORCL\SYSAUX01.DBF
input datafile file number=00006 name=C:\APP\NEERAJS\ORADATA\ORCL\TSPIR.DBF
input datafile file number=00005 name=C:\APP\NEERAJS\ORADATA\ORCL\EXAMPLE01.DBF
input datafile file number=00003 name=C:\APP\NEERAJS\ORADATA\ORCL\UNDOTBS01.DBF
input datafile file number=00004 name=C:\APP\NEERAJS\ORADATA\ORCL\USERS01.DBF
channel ORA_DISK_1: starting piece 1 at 30-NOV-11
channel ORA_DISK_1: finished piece 1 at 30-NOV-11
piece handle=F:\RMAN_BKP\02MSV70H_1_1 tag=TAG20111130T143705 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:01:55
Finished backup at 30-NOV-11

Starting backup at 30-NOV-11
current log archived
using channel ORA_DISK_1
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=15 RECID=13 STAMP=768580741
channel ORA_DISK_1: starting piece 1 at 30-NOV-11
channel ORA_DISK_1: finished piece 1 at 30-NOV-11
piece handle=F:\RMAN_BKP\04MSV746_1_1 tag=TAG20111130T143901 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 30-NOV-11

Starting Control File and SPFILE Autobackup at 30-NOV-11
piece handle=F:\RMAN_BKP\CF\C-1296005542-20111130-01 comment=NONE
Finished Control File and SPFILE Autobackup at 30-NOV-11

Step 4  :  Note the SCN and drop the tablespace 

SQL> select current_scn from v$database;
CURRENT_SCN
-----------------
    5659022

SQL> drop tablespace tspir including contents and datafiles;
Tablespace dropped.

Step  5  :  Connect with rman and perform TSPIR  

Here we have used the auxiliary destination with the recover tablespace command because auxiliary  destination is an  optional disk location where RMAN uses to temporarily store the auxiliary set files. The auxiliary destination is used only when using a RMAN-managed auxiliary instance. Specifying an auxiliary destination with a user-managed auxiliary instance results in an error.

C:\>rman target sys/xxxx@orcl
Recovery Manager: Release 11.2.0.1.0 - Production on Wed Nov 30 14:58:11 2011
Copyright (c) 1982, 2009, Oracle and/or its affiliates.  All rights reserved.
connected to target database: ORCL (DBID=1296005542)

RMAN>  recover tablespace tspir  until scn 5659022  auxiliary  destination 'F:\';
Starting recover at 30-NOV-11
using channel ORA_DISK_1
RMAN-05026: WARNING: presuming following set of tablespaces applies to specified point-in-time
List of tablespaces expected to have UNDO segments
Tablespace SYSTEM
Tablespace UNDOTBS1
Creating automatic instance, with SID='nume'
initialization parameters used for automatic instance:
db_name=ORCL
db_unique_name=nume_tspitr_ORCL
compatible=11.2.0.0.0
db_block_size=8192
db_files=200
sga_target=280M
processes=50
db_create_file_dest=F:\
log_archive_dest_1='location=F:\'
#No auxiliary parameter file used
starting up automatic instance ORCL
Oracle instance started
Total System Global Area     292933632 bytes
Fixed Size                     1374164 bytes
Variable Size                100665388 bytes
Database Buffers             184549376 bytes
Redo Buffers                   6344704 bytes
Automatic instance created
List of tablespaces that have been dropped from the target database:
Tablespace tspir
contents of Memory Script:
{
# set requested point in time
set until  scn 5659022;
# restore the controlfile
restore clone controlfile;
# mount the controlfile
sql clone 'alter database mount clone database';
# archive current online log
sql 'alter system archive log current';
# avoid unnecessary autobackups for structural changes during TSPITR
sql 'begin dbms_backup_restore.AutoBackupFlag(FALSE); end;';
}
executing Memory Script
executing command: SET until clause
Starting restore at 30-NOV-11
allocated channel: ORA_AUX_DISK_1
channel ORA_AUX_DISK_1: SID=59 device type=DISK
channel ORA_AUX_DISK_1: starting datafile backup set restore
channel ORA_AUX_DISK_1: restoring control file
channel ORA_AUX_DISK_1: reading from backup piece F:\RMAN_BKP\CF\C-1296005542-20111130-01
channel ORA_AUX_DISK_1: piece handle=F:\RMAN_BKP\CF\C-1296005542-20111130-01 tag=TAG20111130T143903
channel ORA_AUX_DISK_1: restored backup piece 1
channel ORA_AUX_DISK_1: restore complete, elapsed time: 00:00:04
output file name=F:\ORCL\CONTROLFILE\O1_MF_7FD0QK8S_.CTL
Finished restore at 30-NOV-11
sql statement: alter database mount clone database
sql statement: alter system archive log current
sql statement: begin dbms_backup_restore.AutoBackupFlag(FALSE); end;
contents of Memory Script:
{
# set requested point in time
set until  scn 5659022;
# set destinations for recovery set and auxiliary set datafiles
set newname for clone datafile  1 to new;
set newname for clone datafile  3 to new;
set newname for clone datafile  2 to new;
set newname for clone tempfile  1 to new;
set newname for datafile  6 to
 "C:\APP\NEERAJS\ORADATA\ORCL\TSPIR.DBF";
# switch all tempfiles
switch clone tempfile all;
# restore the tablespaces in the recovery set and the auxiliary set
restore clone datafile  1, 3, 2, 6;
switch clone datafile all;
}
executing Memory Script
executing command: SET until clause
executing command: SET NEWNAME
executing command: SET NEWNAME
executing command: SET NEWNAME
executing command: SET NEWNAME
executing command: SET NEWNAME
renamed tempfile 1 to F:\ORCL\DATAFILE\O1_MF_TEMP_%U_.TMP in control file
Starting restore at 30-NOV-11
using channel ORA_AUX_DISK_1
channel ORA_AUX_DISK_1: starting datafile backup set restore
channel ORA_AUX_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_AUX_DISK_1: restoring datafile 00001 to F:\ORCL\DATAFILE\O1_MF_SYSTEM_%U_.DBF
channel ORA_AUX_DISK_1: restoring datafile 00003 to F:\ORCL\DATAFILE\O1_MF_UNDOTBS1_%U_.DBF
channel ORA_AUX_DISK_1: restoring datafile 00002 to F:\ORCL\DATAFILE\O1_MF_SYSAUX_%U_.DBF
channel ORA_AUX_DISK_1: restoring datafile 00006 to C:\APP\NEERAJS\ORADATA\ORCL\TSPIR.DBF
channel ORA_AUX_DISK_1: reading from backup piece F:\RMAN_BKP\02MSV70H_1_1
channel ORA_AUX_DISK_1: piece handle=F:\RMAN_BKP\02MSV70H_1_1 tag=TAG20111130T143705
channel ORA_AUX_DISK_1: restored backup piece 1
channel ORA_AUX_DISK_1: restore complete, elapsed time: 00:02:15
Finished restore at 30-NOV-11
datafile 1 switched to datafile copy
input datafile copy RECID=5 STAMP=768585055 file name=F:\ORCL\DATAFILE\O1_MF_SYSTEM_7FD0QYNZ_.DBF
datafile 3 switched to datafile copy
input datafile copy RECID=6 STAMP=768585056 file name=F:\ORCL\DATAFILE\O1_MF_UNDOTBS1_7FD0QYRF_.DBF
datafile 2 switched to datafile copy
input datafile copy RECID=7 STAMP=768585056 file name=F:\ORCL\DATAFILE\O1_MF_SYSAUX_7FD0QYPG_.DBF
contents of Memory Script:
{
# set requested point in time
set until  scn 5659022;
# online the datafiles restored or switched
sql clone "alter database datafile  1 online";
sql clone "alter database datafile  3 online";
sql clone "alter database datafile  2 online";
sql clone "alter database datafile  6 online";
# recover and open resetlogs
recover clone database tablespace  "TSPIR", "SYSTEM", "UNDOTBS1", "SYSAUX" delete archivelog;
alter clone database open resetlogs;
}
executing Memory Script
executing command: SET until clause
sql statement: alter database datafile  1 online
sql statement: alter database datafile  3 online
sql statement: alter database datafile  2 online
sql statement: alter database datafile  6 online
Starting recover at 30-NOV-11
using channel ORA_AUX_DISK_1
starting media recovery
archived log for thread 1 with sequence 15 is already on disk as file D:\ARCHIVE\ORCL_ARCHIVE\ARC0000000015_0768224813.0001
archived log for thread 1 with sequence 16 is already on disk as file D:\ARCHIVE\ORCL_ARCHIVE\ARC0000000016_0768224813.0001
archived log file name=D:\ARCHIVE\ORCL_ARCHIVE\ARC0000000015_0768224813.0001 thread=1 sequence=15
archived log file name=D:\ARCHIVE\ORCL_ARCHIVE\ARC0000000016_0768224813.0001 thread=1 sequence=16
media recovery complete, elapsed time: 00:00:04
Finished recover at 30-NOV-11
database opened
contents of Memory Script:
{
# make read only the tablespace that will be exported
sql clone 'alter tablespace  TSPIR read only';
# create directory for datapump import
sql "create or replace directory TSPITR_DIROBJ_DPDIR as ''
F:\''";
# create directory for datapump export
sql clone "create or replace directory TSPITR_DIROBJ_DPDIR as ''
F:\''";
}
executing Memory Script
sql statement: alter tablespace  TSPIR read only
sql statement: create or replace directory TSPITR_DIROBJ_DPDIR as ''F:\''
sql statement: create or replace directory TSPITR_DIROBJ_DPDIR as ''F:\''
Performing export of metadata...
   EXPDP> Starting "SYS"."TSPITR_EXP_nume":
   EXPDP> Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
   EXPDP> Processing object type TRANSPORTABLE_EXPORT/TABLE
   EXPDP> Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
   EXPDP> Master table "SYS"."TSPITR_EXP_nume" successfully loaded/unloaded
   EXPDP> ******************************************************************************
   EXPDP> Dump file set for SYS.TSPITR_EXP_nume is:
   EXPDP>   F:\TSPITR_NUME_43731.DMP
   EXPDP> ******************************************************************************
   EXPDP> Datafiles required for transportable tablespace TSPIR:
   EXPDP>   C:\APP\NEERAJS\ORADATA\ORCL\TSPIR.DBF
   EXPDP> Job "SYS"."TSPITR_EXP_nume" successfully completed at 16:20:28
Export completed
contents of Memory Script:
{
# shutdown clone before import
shutdown clone immediate
}
executing Memory Script
database closed
database dismounted
Oracle instance shut down
Performing import of metadata...
   IMPDP> Master table "SYS"."TSPITR_IMP_nume" successfully loaded/unloaded
   IMPDP> Starting "SYS"."TSPITR_IMP_nume":
   IMPDP> Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
   IMPDP> Processing object type TRANSPORTABLE_EXPORT/TABLE
   IMPDP> Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
   IMPDP> Job "SYS"."TSPITR_IMP_nume" successfully completed at 16:21:48
Import completed
contents of Memory Script:
{
# make read write and offline the imported tablespaces
sql 'alter tablespace  TSPIR read write';
sql 'alter tablespace  TSPIR offline';
# enable autobackups after TSPITR is finished
sql 'begin dbms_backup_restore.AutoBackupFlag(TRUE); end;';
}
executing Memory Script
sql statement: alter tablespace  TSPIR read write
sql statement: alter tablespace  TSPIR offline
sql statement: begin dbms_backup_restore.AutoBackupFlag(TRUE); end;
Removing automatic instance
Automatic instance removed
auxiliary instance file F:\ORCL\DATAFILE\O1_MF_TEMP_7FD0Y3PY_.TMP deleted
auxiliary instance file F:\ORCL\ONLINELOG\O1_MF_4_7FD0XROZ_.LOG deleted
auxiliary instance file F:\ORCL\ONLINELOG\O1_MF_3_7FD0XK9R_.LOG deleted
auxiliary instance file F:\ORCL\ONLINELOG\O1_MF_2_7FD0X9RF_.LOG deleted
auxiliary instance file F:\ORCL\ONLINELOG\O1_MF_1_7FD0X2LK_.LOG deleted
auxiliary instance file F:\ORCL\DATAFILE\O1_MF_SYSAUX_7FD0QYPG_.DBF deleted
auxiliary instance file F:\ORCL\DATAFILE\O1_MF_UNDOTBS1_7FD0QYRF_.DBF deleted
auxiliary instance file F:\ORCL\DATAFILE\O1_MF_SYSTEM_7FD0QYNZ_.DBF deleted
auxiliary instance file F:\ORCL\CONTROLFILE\O1_MF_7FD0QK8S_.CTL deleted
Finished recover at 30-NOV-11
RMAN>

Step  6  : Check the tablepsace status and existance 

SQL> select tablespace_name,status from dba_tablespaces;
TABLESPACE_NAME                 STATUS
-------------------------                -----------
SYSTEM                                      ONLINE
SYSAUX                                      ONLINE
UNDOTBS1                                 ONLINE
TEMP                                           ONLINE
USERS                                         ONLINE
EXAMPLE                                   ONLINE
TSPIR                                          OFFLINE

Since, we find the tablepspace "TSPIR" is offline . So bring the tablespace online .

SQL> alter tablespace tspir online;
Tablespace altered.

SQL> alter database datafile 'C:\app\neerajs\oradata\orcl\tspir.dbf' online;
Database altered.

SQL> select table_name from dba_tables where tablespace_name='TSPIR';
TABLE_NAME
-----------------
TEST
EMP

SQL> select * from tspir.test;
        ID
----------
        12
       121

SQL> select count(*) from tspir.emp;
  COUNT(*)
----------
         2

Hence , we find that both the tables are recovered



Enjoy     :-) 

ORA-19852: Error creating services for auxiliary instance

This error  generally occur when we go for TSPIR(tablespace point-in-time recovery) . When we issue the "recover tablespace ... "  command we get this error as

RMAN> recover tablespace tspir  until scn 5659022 auxiliary destination 'F:\';
Starting recover at 30-NOV-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=64 device type=DISK
RMAN-05026: WARNING: presuming following set of tablespaces applies to specified point-in-time
List of tablespaces expected to have UNDO segments
Tablespace SYSTEM
Tablespace UNDOTBS1
Creating automatic instance, with SID='tAbD'
RMAN-00571: ========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===========
RMAN-00571: ========================================================
RMAN-03002:failure of recover command at 11/30/2011 14:56:13
ORA-19852:error creating services for auxiliary instance tAbD (error 0)
ORA-27302: failure occurred at:
ORA-27303:additional information: failed to start instance

This error occur because the previous failed TSPITR attempt wasn't cleaned up properly . Therefore to solve this issue, we have to clean the failed TSPIR attempts .Issue the following procedure to clean up the previous failed auxiliary creation attempt:

SQL> exec dbms_backup_restore.manageauxinstance ('TSPITR',1) ;
PL/SQL procedure successfully completed.



Enjoy      :-) 

ORA-7445 Internal Error

An ORA-7445 is a generic error, and can occur from anywhere in the Oracle code. The precise location of the error is identified by the core file and/or trace file it produces. Whenever an ORA-7445 error is raised a core file is generated. There may be a trace file generated with the error as well.

Prior to 11g, the core files are located in the CORE_DUMP_DEST directory. Starting with 11g, there is a new advanced fault diagnosability infrastructure to manage trace data. Diagnostic files are written into a root directory for all diagnostic data called the ADR home. Core files at 11g will go to the ADR HOME/cdump directory

For more Indispensability check the below :

1. Check the Alert Log  :    The alert log may indicate additional errors or other internal errors at the time of the problem. In some cases, the ORA-7445 error will occur along with ORA-600, ORA-3113, ORA-4030 errors. The ORA-7445 error can be side effects of the other problems and we should review the first error and associated core file or trace file and work down the list of errors. 

If the ORA-7445 errors are not associated with other error conditions, ensure the trace data is not truncated. If we see a message at the end of the file “MAX DUMP FILE SIZE EXCEEDED" . the MAX_DUMP_FILE_SIZE parameter is not setup high enough or to ‘unlimited’. There could be vital diagnostic information missing in the file and discovering the root issue may be very difficult. Set the MAX_DUMP_FILE_SIZE appropriately and regenerate the error for complete trace information.

2. Search 600/7445 Lookup Tool  :  Visit My Oracle Support to access the ORA-00600 Lookup tool (Note 7445.1). The ORA-600/ORA-7445 Lookup tool may lead you to applicable content in My Oracle Support on the problem and can be used to investigate the problem with argument data from the error message or we  can pull out key stack pointers from the associated trace file to match up against known bugs.

3. “Fine tune” searches in Knowledge Base  :   As the ORA-7445 error indicates an unhandled exception in the Oracle source code, our search in the Oracle Knowledge Base will need to focus on the stack data from the core file or the trace file.

Keep in mind that searches on generic argument data will bring back a large result set . The more we can learn about the environment and code leading to the errors, the easier it will be to narrow the hit list to match our problem.

4  .  If assistance is required from Oracle  :    Should it become necessary to get assistance from Oracle Support on an ORA-7445 problem, please provide at a minimum, the 

• Alert log
• Associated tracefile(s) or incident package at 11g
• Patch level information
• Core file(s)
• Information about changes in configuration and/or application prior to issues
• If error is reproducible, a self-contained reproducible testcase: Note.232963.1 How to Build a Testcase for Oracle Data Server Support to Reproduce ORA-600 and ORA-7445 Errors.
• RDA report or Oracle Configuration Manager information

Enjoy     :-) 

Estimate the Optimal UNDO Tablespace size in Oracle

We can size the undo tablespace appropriately either by using automatic extension of the undo tablespace or by using the Undo Advisor for a fixed sized tablespace.If we have decided on a fixed-size undo tablespace, the Undo Advisor can help us to estimate needed capacity.The Undo Advisor relies for its analysis on data collected in the Automatic Workload Repository (AWR). It is therefore important that the AWR have adequate workload statistics available so that the Undo Advisor can make accurate recommendations. 

Below is the script which will estiate the size of the undo tablespace required and also provide the detail when the database face the Number of "ORA-01555 (Snapshot too old)" encountered since the last startup of the instance 

SQL> SELECT  d.undo_size/(1024*1024) “ACTUAL UNDO SIZE [MByte]“,
                        SUBSTR(e.value,1,25) “UNDO RETENTION [Sec]“,
                       (TO_NUMBER(e.value) * TO_NUMBER(f.value) *
                      g.undo_block_per_sec) / (1024*1024)  “NEEDED UNDO SIZE [MByte]“
  FROM        (SELECT SUM(a.bytes) undo_size  FROM v$datafile a,  v$tablespace b,
                     dba_tablespaces c
 WHERE      c.contents = 'UNDO'
 AND          c.status = 'ONLINE'
 AND          b.name = c.tablespace_name
AND           a.ts# = b.ts#  ) d, v$parameter e, v$parameter f,
                 ( SELECT MAX(undoblks/((end_time-begin_time)*3600*24))  undo_block_per_sec
FROM       v$undostat  ) g 
WHERE      e.name = 'undo_retention'
AND         f.name = 'db_block_size'
/
set feedback off
set heading off
set lines 132
declare
  cursor get_undo_stat is
         select d.undo_size/(1024*1024) "C1",
                substr(e.value,1,25)    "C2",
                (to_number(e.value) * to_number(f.value) *
g.undo_block_per_sec) / (1024*1024) "C3",
                round((d.undo_size / (to_number(f.value) *
g.undo_block_per_sec)))             "C4"
           from (select sum(a.bytes) undo_size
                   from v$datafile      a,
                        v$tablespace    b,
                        dba_tablespaces c
                  where c.contents = 'UNDO'
                    and c.status = 'ONLINE'
                    and b.name = c.tablespace_name
                    and a.ts# = b.ts#)  d,
                v$parameter e,
                v$parameter f,
                (select max(undoblks/((end_time-begin_time)*3600*24))
undo_block_per_sec from v$undostat)  g
          where e.name = 'undo_retention'
            and f.name = 'db_block_size';
begin
dbms_output.put_line(chr(10)||chr(10)||chr(10)||chr(10) ||
'To optimize UNDO we have two choices :');
dbms_output.put_line('==========================================' || chr(10));
  for rec1 in get_undo_stat loop
      dbms_output.put_line('A)
Adjust UNDO tablespace size according to UNDO_RETENTION :'
|| chr(10));
      dbms_output.put_line(rpad('ACTUAL UNDO SIZE ',65,'.')|| ' : ' ||
TO_CHAR(rec1.c1,'999999') || ' MEGS');
      dbms_output.put_line(rpad('OPTIMAL UNDO SIZE WITH ACTUAL UNDO_RETENTION
(' || ltrim(TO_CHAR(rec1.c2/60,'999999'))
 || ' MINUTES)
',65,'.') || ' : ' || TO_CHAR(rec1.c3,'999999') || ' MEGS');
      dbms_output.put_line(chr(10));
      dbms_output.put_line('B) Adjust UNDO_RETENTION according to UNDO tablespace size :'
|| chr(10));
      dbms_output.put_line(rpad('ACTUAL UNDO RETENTION ',65,'.') ||
' : ' || TO_CHAR(rec1.c2/60,'999999') || ' MINUTES');
      dbms_output.put_line(rpad('OPTIMAL UNDO RETENTION WITH ACTUAL UNDO SIZE
(' || ltrim(TO_CHAR(rec1.c1,'999999')) || ' MEGS) ',65,'.') || ' : ' ||
TO_CHAR(rec1.c4/60,'999999') || ' MINUTES');
  end loop;
dbms_output.put_line(chr(10)||chr(10));
end;
/
select 'Number of "ORA-01555 (Snapshot too old)" encountered since
the last startup of the instance : ' || sum(ssolderrcnt)
from v$undostat;


Enjoy   :-) 

How to resize redolog file in oracle

Once , i receive the e-mail regarding the resize of the redo log file . The Sender want the easiest way to size the redo log file something like 'alter database logfile group 1 '?\redo01.log resize 100m '  or using some other trick . 

We cannot resize the redo log files. We must drop the redolog file and recreate them .This is only method to resize the redo log files. A database requires atleast two groups of redo log files,regardless the number of the members. We cannot the drop the redo log file if its status is current or active . We have change the status to "inactive" then only we can drop it.

When a redo log member is dropped from the database, the operating system file is not deleted from disk. Rather, the control files of the associated database are updated to drop the member from the database structure. After dropping a redo log file, make sure that the drop completed successfully, and then use the appropriate operating system command to delete the dropped redo log file. In my case i have four redo log files and they are of 50MB in size .I will resize to 100 MB.  Below are steps to resize the redo log files.

Step 1 : Check the Status of Redo Logfile 
SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES    ARC    STATUS
----------    ----------    ----------      -----       -------------
         1          5   52428800      YES          INACTIVE
         2          6   52428800      YES          ACTIVE
         3          7   52428800      NO          CURRENT
         4          4   52428800     YES          INACTIVE

Here,we cannot drop the current and active redo log file .

Step  2 :  Forcing a Checkpoint  :

The SQL statement alter system checkpoint explicitly forces Oracle to perform a checkpoint for either the current instance or all instances. Forcing a checkpoint ensures that all changes to the database buffers are written to the datafiles on disk .A global checkpoint is not finished until all instances that require recovery have been recovered.

SQL> alter system checkpoint global ;
system altered.

SQL> select group#,sequence#,bytes,archived,status from v$log;

    GROUP#    SEQUENCE#        BYTES    ARC       STATUS
----------    ----------    ----------    -----     ----------------
         1          5       52428800     YES      INACTIVE
         2          6      52428800     YES       INACTIVE
         3          7      52428800     NO       CURRENT
         4          4      52428800    YES       INACTIVE
Since the status of group 1,2,4 are inactive .so we will drop the group 1 and group 2 redo log file.

Step  3  :  Drop Redo Log File : 
SQL> alter database drop logfile group 1;
Database altered.

SQL> alter database drop logfile group 2;
Database altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES    ARC    STATUS
----------    ----------    ----------    ---     ----------------
         3          7               52428800      NO       CURRENT
         4          4             52428800       YES      INACTIVE

Step  4  : Create new redo log file 

If we don't delete the old redo logfile by OS command when creating the log file with same name then face the below error . Therefore to solve it delete the file by using OS command .

SQL> alter database add logfile group 1 'C:\app\neerajs\oradata\orcl\redo01.log' size 100m;
alter database add logfile group 1 'C:\app\neerajs\oradata\orcl\redo01.log' size 100m
*
ERROR at line 1:
ORA-00301: error in adding log file 'C:\app\neerajs\oradata\orcl\redo01.log' - file cannot be created
ORA-27038: created file already exists
OSD-04010: <create> option specified, file already exists

SQL> alter database add logfile group 1 'C:\app\neerajs\oradata\orcl\redo01.log' size 100m;
Database altered.

SQL> alter database add logfile group 2 'C:\app\neerajs\oradata\orcl\redo02.log' size 100m;
Database altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#      SEQUENCE#      BYTES     ARC       STATUS
----------    ----------     ----------       ---      ----------------
         1          0      104857600       YES     UNUSED
         2          0      104857600       YES     UNUSED
         3          7       52428800        NO      CURRENT
         4          4       52428800       YES      INACTIVE

Step 5 :  Now drop the remaining two old redo log file 
SQL> alter system switch logfile ;
System altered.

SQL> alter system switch logfile ;
System altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES ARC STATUS
---------- ---------- ---------- --- ----------------
         1          8  104857600     YES     ACTIVE
         2          9  104857600     NO      CURRENT
         3          7   52428800     YES     ACTIVE
         4          4   52428800     YES     INACTIVE

SQL> alter system checkpoint global;
System altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES ARC STATUS
---------- ---------- ---------- --- ----------------
         1          8    104857600     YES     INACTIVE
         2          9    104857600     NO     CURRENT
         3          7     52428800     YES     INACTIVE
         4          4     52428800    YES      INACTIVE

SQL> alter database drop logfile group 3;
Database altered.

SQL> alter database drop logfile group 4;
Database altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES ARC STATUS
---------- ---------- ---------- --- ----------------
         1          8  104857600      YES      INACTIVE
         2          9  104857600      NO       CURRENT

Step 6 : Create the redo log file 
SQL> alter database add logfile group 3 'C:\app\neerajs\oradata\orcl\redo03.log' size 100m;
Database altered.

SQL> alter database add logfile group 4 'C:\app\neerajs\oradata\orcl\redo04.log' size 100m;
Database altered.

SQL>  select group#,sequence#,bytes,archived,status from v$log;
    GROUP#  SEQUENCE#      BYTES ARC STATUS
---------- ---------- ---------- --- ----------------
         1          8        104857600      YES       INACTIVE
         2          9        104857600      NO        CURRENT
         3          0        104857600     YES        UNUSED
         4          0        104857600     YES        UNUSED


Enjoy    :-)