Saturday, February 18, 2012

Database Refresh

List me some of the High Availability concepts.
Technologies which reduce the downtime of systems are called as HA concepts.
  • Backups
  • Clusters
  • Disaster Recovery site

What is Database Refresh?
  • The Process of refreshing the Data from one System with another System Data is called as DB Refresh
  • Once getting approvals need to check any user log-din in the system. And inform to users system will going to be down, log-out their sessions. if anyone still running need to terminate them. Then perform the refresh activity.
  •  The four steps need to be performed to complete the Refresh Successfully  

Briefly explain me the process of Database Refresh/System copy/System refresh?
  • Primary site: [Production system]
1.      Need to take full back up of Database
2.      Need to take Control file backup
  • Secondary site: [Quality system]
1.      Backup of needed information in the Secondary system
2.      Database restore
3.      Control file script creation and execution in nomount state.
4.      Recovery
5.      Database open using resetlogs or noresetlogs.
  • Commands used:
1.      Alter database backup controlfile to trace;
2.      Alter database recover using backup controlfile until cancel;
3.      Alter database open resetlogs / noresetlogs;
  • Disadvantages:
1.      If any disaster occurs data can’t be recovered upto the point. The last redo logs will be missing when the disaster has occurred. We need maintain the redo logs with a low size, so that redo logs occur frequently and most changes will be moved and applied in Standby database.
  • Support packs             No need to apply
  • License                        Need to applied as the hardware key changes from system t                                     to system
  • Kernel patches                        Need to be applied as it is an different independent system
What role did you play in maintenance of DRS?
  • My role involved in verifying the transfer of redo logs and checking whether the redo logs moved are correctly applied or not by keeping the standby database in Read-Only mode.
  • Checking involves creating a new dummy user and locking that user in the primary site and we need to move that redo log to the secondary site. After applying that redo log we need to keep the standby database in Read-Only mode and execute the command Select uflag, username from usr02 where username like ‘XXXX’; the uflag must show 64, which indicate that the it is an administrative lock.
  • Commands used:
Alter system archive log current;

If a problem occurs during recovery what will you check?
  • Check whether the RECO process is running or not, using the command
    • ps –ef | grep RECO.
  • Check whether the required redo log is available or not.

How can you bring a database from archivelog to noarchivelog and vice-versa?
  • Process:
1.      Changes in parameter file. Log_archive_start=True/False
2.      Database down
3.      Execute Alter database archivelog/noarchivelog; in nomount state.
4.      Database Open

Can you shift from noarchive mode to archive mode Online?
  • Yes, using the command Alter system archive log start;


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