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An Alternative Method for Oracle Physical Standby

Physical Standby Server can be used to recover data from disaster is one of the best methods. But the installation and management may be a little bit difficult. There is an another way.

First i should specify properties of the primary and recovery databases.
Primary server name: primsrv
Instance name: orcl
Primary server: ORACLE_BASE: /u01/app/oracle
Primary server: ORACLE_HOME: /u01/app/oracle/product/10.2.0/db_1
Primary server datafile location: /database/oradata/orcl
Primary server redolog file location: /database/oradata/orcl
Primary server controlfile location: /database/oradata/orcl
Primary server backup location (will be mounted by recovery server via nfs with the same folder name): /backup/rman_bck
Primary server archivelog destination (will be mounted by recovery server via nfs with the same folder name): /fra/arch/orcl
Recovery server name: recovsrv
And other properties of the recovery server database will be same of the primary server.

Now i can install recovery server.
First i should install an operating system same as the primary server and prepare folder structure where the datafiles, redologs and controlfiles exist. In this example it is /database/oradata/orcl folder. Then i should install same version of oracle software only as the primary server has. After installing oracle software i should create database instance exactly same as the primary server’s instance using dbca tool. I should be careful for specifying the right locations for datafiles, redologs and controlfiles. I also should be careful for specifying the right parameters of the database like character set, log_archive_dest_1, log_archive_format.

Now i have two oracle databases have the same structures. But how can i recover primary server to the recovery server? First i need to provide recovery server to see primary server’s /backup/rman_bck and /fra/arch/orcl folders. I can do it using nfs. With nfs sharing, recovery server can see primary server’s folders.

Recovery server’s /etc/fstab configuration should be look like this.
primsrv:/backup              /backup               nfs …..
primsrv:/fra/arch/orcl      /fra/arch/orcl    nfs ……

At recovery server shutdown database and remove datafiles and controlfiles.
recovsrv SQL> shutdown immediate
recovsrv #> cd /database/oradata/orcl
recovsrv #> rm –f *.dbf
recovsrv #> rm –f *.ctl

At primary server take backup of controlfile and initialization file then send it to the recovery server
primsrv SQL> alter database backup controlfile to '/home/oracle/primorcl.ctl';
primsrv SQL> create pfile='/home/oracle/initprim.ora' from spfile;
primsrv #> scp /home/oracle/primsrv.ctl oracle@recovsrv:/database/oradata/orcl
primsrv #> scp /home/oracle/initprim.ora oracle@recovsrv:/home/oracle

At recovery server make copies of the backup controlfile and create spfile from pfile. Then startup database at mount state, restore and recover database.
recovsrv #> cd /database/oradata/orcl
recovsrv #> mv primorcl.ctl control01.ctl
recovsrv #> cp control01.ctl control02.ctl
recovsrv #> cp control01.ctl control03.ctl
recovsrv SQL> create spfile from pfile='/home/oracle/initprim.ora';
recovsrv SQL> startup mount
recovsrv RMAN> restore database
recovsrv SQL> recover database using backup controlfile until cancel

There is a parameter named archive_lag_target used to switch archivelog files periodically. I can set this parameter to apply most recent changes in the primary server to recovery server. At primary server set archive_lag_target parameter to 900 second.
primsrv SQL> alter system set archive_lag_target=900 scope both;

So I can setup a cron job that executes recovery process every 15 minutes. At recovery server
recovsrv #> crontab -l
*/15 * * * * /home/oracle/scripts/

recovsrv #> more /home/oracle/scripts/
export PATH
sqlplus "/ as sysdba" @/home/oracle/scripts/recov.sql

recovsrv #> more /home/oracle/scripts/recov.sql
set autorecovery on
spool /home/oracle/scripts/recov.lst
recover database using backup controlfile until cancel;

At recovery server when cron job runs, i can tail output
recovsrv #> tail -f /home/oracle/scripts/recov.lst
tail: recov.lst: file truncated

ORA-00279: change 137823348 generated at 12/23/2010 18:02:56 needed for thread
ORA-00289: suggestion : /fra/arch/orcl/arch_728088008_1_8238.arc
ORA-00280: change 137823348 for thread 1 is in sequence #8238
ORA-00278: log file ‘/fra/arch/orcl/arch_728088008_1_8237.arc’ no longer
needed for this recovery

ORA-00279: change 137828288 generated at 12/23/2010 18:17:57 needed for thread
ORA-00289: suggestion : /fra/arch/orcl/arch_728088008_1_8239.arc
ORA-00280: change 137828288 for thread 1 is in sequence #8239
ORA-00278: log file ‘/fra/arch/orcl/arch_728088008_1_8238.arc’ no longer
needed for this recovery

ORA-00308: cannot open archived log ‘/fra/arch/orcl/arch_728088008_1_8239.arc’
ORA-27037: unable to obtain file status
Linux-x86_64 Error: 2: No such file or directory
Additional information: 3

As you see the output, archivelogs will be applied every 15 minutes on the recovery server.

Important note: If i would like to open recovery server for transactions, i have to execute alter database open resetlogs command. In case of a failure, i have a ready database for business continuity.


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