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Standby Database

May 21, 2012 Leave a comment

Data Guard promises:

  • Disaster recovery
  • High availability
  • Data protection
  • Flexible balancing between data protection and performance requirements
  •  Simple management through the data guard broker.
  • Gap detection

Advantages:

1. Very low failure rate
All system components are duplicated. The primary and standby instances can run on different hosts. They can also have separate locations depending on the safety requirements.

2. Very short downtime

If an error occurs in the primary database system and you have to recover the database, you can perform the recovery very quickly on the standby host. You can avoid the time-consuming datafile restore, since these files are already located on the standby host.

The only thing you need to do is to import the last entries from the redo log files. Therefore, the standby instance can take over the tasks of the primary instance very quickly.

3. Significant decrease of the load on the production host

The database backup requires considerable resources and time for large databases. Since the backup can run on the standby host, the load on the primary instance is reduced significantly.
Therefore, the resources on the production host are fully available for production operation, and you do not need to interrupt or restrict database operation for a backup.

4. Consistency

Applying redo log files to the standby database immediately verifies their consistency. No other tool can achieve this level of verification.

Disadvantages:

1. High costs

For a standby database scenario, all system components need to be available in duplicate. In particular, duplicate hardware resources (CPU, hard disks, and so on) are expensive.

2. High system administration expense

You need to set up the standby host. If structural changes are made on the primary database system, you must make the required resources are available on the standby host. When the standby instance has taken over production operation – a “takeover” – you must set up a replacement standby database.

3. High requirements for switchover software

So that the standby instance can take over production operation, the appropriate switchover software is required. The user and the suppliers of the hardware and system software are responsible for selecting this software and making sure that it functions correctly.

Step-by-step instructions on how to create a Physical Standby Database on Windows and UNIX servers, and maintenance tips on the databases in a Data Guard Environment:

(Article by Hailie Jiao )

In this example the database version is 10.2.0.3.. The Primary database and Standby database are located on different machines at different sites. The Primary database is called PRIM and the Standby database is called STAN. I use Flash Recovery Area, and OMF.

a) Setup the environment

1. Make sure the operating system and platform architecture on the primary and standby systems are the same.
2. Install Oracle database software without the starter database on the standby server and patch it if necessary. Make sure the same Oracle software release is used on the Primary and Standby databases, and Oracle home paths are identical.
3. Test the Standby Database creation on a test environment first before working on the Production database.

b) On the Primary Database Side

1. Enable forced logging on your primary database:

SQL> ALTER DATABASE FORCE LOGGING;

2. Create a password file if it doesn’t exist.
1) To check if a password file already exists, run the following command:

SQL> select * from v$pwfile_users;

2) If it doesn’t exist, use the following command to create one:

On Windows:
 $cd %ORACLE_HOME%\database
 $orapwd file=pwdPRIM.ora password=xxxxxxxx force=y
 (Note: Replace xxxxxxxxx with the password for the SYS user.)
On UNIX:
 $Cd $ORACLE_HOME/dbs
 $Orapwd file=pwdPRIM.ora password=xxxxxxxx force=y
 (Note: Replace xxxxxxxxx with your actual password for the SYS user.)

3. Configure a Standby Redo log.

1)  The size of the standby redo log files should match the size of the current Primary database online redo log files. To find out the size of your online redo log files:

SQL> select bytes from v$log;

BYTES
----------
52428800
52428800
52428800

2) Use the following command to determine your current log file groups:

SQL> select group#, member from v$logfile;

3) Create standby Redo log groups.
Primary database had 3 log file groups originally and 3 standby redo log groups are created now using the following commands:

SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 4 SIZE 50M;
SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 5 SIZE 50M;
SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 6 SIZE 50M;

4) To verify the results of the standby redo log groups creation, run the following query:

SQL>select * from v$standby_log;

4. Enable Archiving on Primary.
If your primary database is not already in Archive Log mode, enable the archive log mode:

SQL>shutdown immediate;
SQL>startup mount;
SQL>alter database archivelog;
SQL>alter database open;
SQL>archive log list;

5. Set Primary Database Initialization Parameters

Create a text initialization parameter file (PFILE) from the server parameter file (SPFILE), to add the new primary role parameters.

1) Create pfile from spfile for the primary database:

On Windows:
SQL>create pfile=’\database\pfilePRIM.ora’ from spfile;
(Note- specify your Oracle home path to replace ‘’).
 On UNIX:
SQL>create pfile=’/dbs/pfilePRIM.ora’ from spfile;
(Note- specify your Oracle home path to replace ‘’).
2) Edit pfilePRIM.ora to add the new primary and standby role parameters: (Here the file paths are from a windows system. For UNIX system, specify the path accordingly)

db_name=PRIM
db_unique_name=PRIM
LOG_ARCHIVE_CONFIG='DG_CONFIG=(PRIM,STAN)'
LOG_ARCHIVE_DEST_1=
'LOCATION=F:\Oracle\flash_recovery_area\PRIM\ARCHIVELOG
VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
DB_UNIQUE_NAME=PRIM'
LOG_ARCHIVE_DEST_2=
'SERVICE=STAN LGWR ASYNC
VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
DB_UNIQUE_NAME=STAN'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
LOG_ARCHIVE_FORMAT=%t_%s_%r.arc
LOG_ARCHIVE_MAX_PROCESSES=30
remote_login_passwordfile='EXCLUSIVE'
FAL_SERVER=STAN
FAL_CLIENT=PRIM
STANDBY_FILE_MANAGEMENT=AUTO
# Specify the location of the standby DB datafiles followed by the primary location;
DB_FILE_NAME_CONVERT='E:\oracle\product\10.2.0\oradata\STAN\DATAFILE',
'E:\oracle\product\10.2.0\oradata\PRIM\DATAFILE'
# Specify the location of the standby DB online redo log files followed by the primary location 
LOG_FILE_NAME_CONVERT=’E:\oracle\product\10.2.0\oradata\STAN\ONLINELOG’, 
’E:\oracle\product\10.2.0\oradata\PRIM\ONLINELOG’,
 ’F:\Oracle\flash_recovery_area\STAN\ONLINELOG’,
 ’F:\Oracle\flash_recovery_area\PRIM\ONLINELOG’

6. Create spfile from pfile, and restart primary database using the new spfile.

Data Guard must use SPFILE. Create the SPFILE and restart database.

On windows:
SQL> shutdown immediate;
SQL> startup nomount pfile=’\database\pfilePRIM.ora’;
SQL>create spfile from pfile=’\database\pfilePRIM.ora’;
-- Restart the Primary database using the newly created SPFILE.
SQL>shutdown immediate;
SQL>Startup;
(Note- specify your Oracle home path to replace ‘’).
On UNIX:
SQL> shutdown immediate;
SQL> startup nomount pfile=’/dbs/pfilePRIM.ora’;
SQL>create spfile from pfile=’/dbs/pfilePRIM.ora’;
-- Restart the Primary database using the newly created SPFILE.
SQL>shutdown immediate;
SQL>Startup;

c) On the Standby Database Site:

1. Create a copy of Primary database data files on the Standby Server:
On Primary DB:

SQL>shutdown immediate;

On Standby Server (While the Primary database is shut down):
1) Create directory for data files, for example, on windows,
E:\oracle\product\10.2.0\oradata\STAN\DATAFILE.
On UNIX, create the directory accordingly.

2) Copy the data files and temp files over.

3) Create directory (multiplexing) for online logs, for example, on Windows,
E:\oracle\product\10.2.0\oradata\STAN\ONLINELOG and
F:\Oracle\flash_recovery_area\STAN\ONLINELOG.
On UNIX, create the directories accordingly.

4) Copy the online logs over.

2. Create a Control File for the standby database:
On Primary DB, create a control file for the standby to use:

SQL>startup mount;
SQL>alter database create standby controlfile as ‘STAN.ctl;
SQL>ALTER DATABASE OPEN;

3. Copy the Primary DB pfile to Standby server and rename/edit the file.

1) Copy pfilePRIM.ora from Primary server to Standby server, to database folder on Windows or dbs folder on UNIX under the Oracle home path.
2) Rename it to pfileSTAN.ora, and modify the file as follows. : (Here the file paths are from a windows system. For UNIX system, specify the path accordingly)

*.audit_file_dest='E:\oracle\product\10.2.0\admin\STAN\adump'
 *.background_dump_dest='E:\oracle\product\10.2.0\admin\STAN\bdump'
 *.core_dump_dest='E:\oracle\product\10.2.0\admin\STAN\cdump'
 *.user_dump_dest='E:\oracle\product\10.2.0\admin\STAN\udump'
 *.compatible='10.2.0.3.0'
 control_files='E:\ORACLE\PRODUCT\10.2.0\ORADATA\STAN\CONTROLFILE\STAN.CTL','F:\ORACLE\FLASH_RECOVERY_AREA\STAN\CONTROLFILE\STAN.CTL'
 db_name='PRIM'
 db_unique_name=STAN
 LOG_ARCHIVE_CONFIG=’DG_CONFIG=(PRIM,STAN)’
 LOG_ARCHIVE_DEST_1=
 ‘LOCATION=F:\Oracle\flash_recovery_area\STAN\ARCHIVELOG
 VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
 DB_UNIQUE_NAME=STAN’
 LOG_ARCHIVE_DEST_2=
 ‘SERVICE=PRIM LGWR ASYNC
 VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
 DB_UNIQUE_NAME=PRIM’
 LOG_ARCHIVE_DEST_STATE_1=ENABLE
 LOG_ARCHIVE_DEST_STATE_2=ENABLE
 LOG_ARCHIVE_FORMAT=%t_%s_%r.arc
 LOG_ARCHIVE_MAX_PROCESSES=30
 FAL_SERVER=PRIM
 FAL_CLIENT=STAN
 remote_login_passwordfile='EXCLUSIVE'
 # Specify the location of the primary DB datafiles followed by the standby location
 DB_FILE_NAME_CONVERT=’E:\oracle\product\10.2.0\oradata\PRIM\DATAFILE’,
 ’E:\oracle\product\10.2.0\oradata\STAN\DATAFILE’
 # Specify the location of the primary DB online redo log files followed by the standby location
 LOG_FILE_NAME_CONVERT=’E:\oracle\product\10.2.0\oradata\PRIM\ONLINELOG’,
 ’E:\oracle\product\10.2.0\oradata\STAN\ONLINELOG’,
 ’F:\Oracle\flash_recovery_area\PRIM\ONLINELOG’,
 ’F:\Oracle\flash_recovery_area\STAN\ONLINELOG’
 STANDBY_FILE_MANAGEMENT=AUTO
(Note: Not all the parameter entries are listed here.)

4. On Standby server, create all required directories for dump and archived log destination:
Create directories adump, bdump, cdump, udump, and archived log destinations for the standby database.

5. Copy the standby control file ‘STAN.ctl’ from primary to standby destinations

6. Copy the Primary password file to standby and rename it to pwdSTAN.ora.
On Windows copy it to \database folder, and on UNIX copy it to /dbs directory. And then rename the password file.

7. For Windows, create a Windows-based services (optional):
$oradim –NEW –SID STAN –STARTMODE manual

8. Configure listeners for the primary and standby databases.

1) On Primary system: use Oracle Net Manager to configure a listener for PRIM and STAN. Then restart the listener.

$lsnrctl stop
$lsnrctl start

2) On Standby server: use Net Manager to configure a listener for PRIM and STAN. Then restart the listener.

$lsnrctl stop
$lsnrctl start

9. Create Oracle Net service names.
1) On Primary system: use Oracle Net Manager to create network service names for PRIM and STAN. Check tnsping to both services:

$tnsping PRIM
$tnsping STAN

2) On Standby system: use Oracle Net Manager to create network service names for PRIM and STAN. Check tnsping to both services:
$tnsping PRIM
$tnsping STAN

10. On Standby server, setup the environment variables to point to the Standby database.

Set up ORACLE_HOME and ORACLE_SID.

11. Start up nomount the standby database and generate a spfile.

On Windows:
 SQL>startup nomount pfile=’\database\pfileSTAN.ora’;
 SQL>create spfile from pfile=’\database\pfileSTAN.ora’;
 -- Restart the Standby database using the newly created SPFILE.
 SQL>shutdown immediate;
 SQL>startup mount;
On UNIX:
 SQL>startup nomount pfile=’/dbs/pfileSTAN.ora’;
 SQL>create spfile from pfile=’/dbs/pfileSTAN.ora’;
 -- Restart the Standby database using the newly created SPFILE.
 SQL>shutdown immediate;
 SQL>startup mount;
 (Note- specify your Oracle home path to replace ‘’).

12. Start Redo apply

1) On the standby database, to start redo apply:

SQL>alter database recover managed standby database disconnect from session;

If you ever need to stop log apply services:

SQL> alter database recover managed standby database cancel;

13. Verify the standby database is performing properly:

1) On Standby perform a query:

SQL>select sequence#, first_time, next_time from v$archived_log;

2) On Primary, force a logfile switch:

SQL>alter system switch logfile;

3) On Standby, verify the archived redo log files were applied:

SQL>select sequence#, applied from v$archived_log order by sequence#;

14. If you want the redo data to be applied as it is received without waiting for the current standby redo log file to be archived, enable the real-time apply.

To start real-time apply:

SQL> alter database recover managed standby database using current logfile disconnect;

15. To create multiple standby databases, repeat this procedure.

d) Maintenance:

1. Check the alert log files of Primary and Standby databases frequently to monitor the database operations in a Data Guard environment.

2. Cleanup the archive logs on Primary and Standby servers.

I scheduled weekly Hot Whole database backup against my primary database that also backs up and delete the archived logs on Primary.

For the standby database, I run RMAN to backup and delete the archive logs once per week.

$rman target /@STAN;
RMAN>backup archivelog all delete input;

To delete the archivelog backup files on the standby server, I run the following once a month:

RMAN>delete backupset;

3. Password management
The password for the SYS user must be identical on every system for the redo data transmission to succeed. If you change the password for SYS on Primary database, you will have to update the password file for Standby database accordingly, otherwise the logs won’t be shipped to the standby server.

Refer to section b) 2, step 2 to update/recreate password file for the Standby database.

Source / Reference Links:

Database and Web Server on the same machine?

May 11, 2012 Leave a comment
Just a thought of having separate servers for database and web landed me on the following links:

My catch:

Single Server

Pros:  Performance gain, less latency time

Cons:  Vulnerable

Separate servers  

Pros:  Security advantage, scalability

Cons: Expense on extra hardware

More on this soon!

Active Connections to Oracle Database

May 3, 2012 Leave a comment

V$SESSION displays session information for each current session.

select
substr(a.spid,1,9) pid,
substr(b.sid,1,5) sid,
substr(b.serial#,1,5) ser#,
substr(b.machine,1,6) box,
substr(b.username,1,10) username,
— b.server,
substr(b.osuser,1,8) os_user,
substr(b.program,1,30) program
from v$session b, v$process a
where
b.paddr = a.addr
and type=’USER’
order by spid;

Source

Categories: General, Uncategorized

Automatic Tuning of Undo Retention and Optimization

May 1, 2012 Leave a comment

Oracle Database automatically tunes the undo retention period based on how the undo tablespace is configured.

If the undo tablespace is fixed size, the database tunes the retention period for the best possible undo retention for that tablespace size and the current system load. This tuned retention period can be significantly greater than the specified minimum retention period.

If the undo tablespace is configured with the AUTOEXTEND option, the database tunes the undo retention period to be somewhat longer than the longest-running query on the system at that time. Again, this tuned retention period can be greater than the specified minimum retention period.

Determine the current retention period by querying the TUNED_UNDORETENTION column of the V$UNDOSTAT view. This view contains one row for each 10-minute statistics collection interval over the last 4 days. (Beyond 4 days, the data is available in the DBA_HIST_UNDOSTAT view.) TUNED_UNDORETENTION is given in seconds.

select to_char(begin_time, 'DD-MON-RR HH24:MI') begin_time,
 to_char(end_time, 'DD-MON-RR HH24:MI') end_time, tuned_undoretention
 from v$undostat order by end_time;
BEGIN_TIME END_TIME TUNED_UNDORETENTION
 --------------- --------------- -------------------
 04-FEB-05 00:01 04-FEB-05 00:11 12100
 ...
 07-FEB-05 23:21 07-FEB-05 23:31 86700
 07-FEB-05 23:31 07-FEB-05 23:41 86700
 07-FEB-05 23:41 07-FEB-05 23:51 86700
 07-FEB-05 23:51 07-FEB-05 23:52 86700
576 rows selected.

Calculating UNDO_RETENTION for given UNDO Tabespace

The following query will helps to optimize the UNDO_RETENTION parameter:

Otimal Undo Retention

 

 

 

 

Image Source

Because these following queries use the V$UNDOSTAT statistics, run the queries only after the database has been running with UNDO for a significant and representative time!

Actual Undo Size

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#;
UNDO_SIZE
----------
 1572864000

Undo Blocks per Second

SELECT MAX(undoblks/((end_time-begin_time)*3600*24))
 "UNDO_BLOCK_PER_SEC"
 FROM v$undostat;
UNDO_BLOCK_PER_SEC
------------------
 249.398333333333333333333333333333333333

DB Block Size

SELECT TO_NUMBER(value) "DB_BLOCK_SIZE [KByte]"
 FROM v$parameter
WHERE name = 'db_block_size';
DB_BLOCK_SIZE [Byte]
--------------------
 8192

Optimal Undo Retention

770 [Sec]

Using Inline Views:

SELECT d.undo_size/(1024*1024) "ACTUAL UNDO SIZE [MByte]",
 SUBSTR(e.value,1,25) "UNDO RETENTION [Sec]",
 ROUND((d.undo_size / (to_number(f.value) *
 g.undo_block_per_sec))) "OPTIMAL UNDO RETENTION [Sec]"
 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'
/
ACTUAL UNDO SIZE [MByte]
------------------------
1500
UNDO RETENTION [Sec]
--------------------
900
OPTIMAL UNDO RETENTION [Sec]
----------------------------
770

Calculating required UNDO Size for given Database Activity

If you are not limited by disk space, then it would be better to choose the UNDO_RETENTION time that is best for you (for FLASHBACK, etc.). Allocate the appropriate size to the UNDO tablespace according to the database activity:

Again, all in one query:

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'
/

ACTUAL UNDO SIZE [MByte]
------------------------
1500
UNDO RETENTION [Sec] 
--------------------
900
NEEDED UNDO SIZE [MByte]
------------------------
1753.582031249999999999999999999999999998

The previous query may return a “NEEDED UNDO SIZE” that is less than the “ACTUAL UNDO SIZE”. If this is the case, you may be wasting space. You can choose to resize your UNDO tablespace to a lesser value or increase your UNDO_RETENTION parameter to use the additional space.

References / Source: