Backup and Recovery
1. Explain the difference between a hot backup and a cold backup and the
benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and
running and it must be in archive log mode. A cold backup is taking a backup of
the database while it is shut down and does not require being in archive log
mode. The benefit of taking a hot backup is that the database is still available for
use while the backup is occurring and you can recover the database to any ball in
time. The benefit of taking a cold backup is that it is typically easier to administer
the backup and recovery process. In addition, since you are taking cold backups
the database does not require being in archive log mode and thus there will be a
slight performance gain as the database is not cutting archive logs to disk.
2· You have just had to restore from backup and do not have any control
files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the
data files where and then issue the recover command with the using backup
control file clause.
3· Explain the difference between ARCHIVELOG mode and NOARCHIVELOG
mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a
backup of all transactions that have occurred in the database so that you can
recover to any ball in time. NOARCHIVELOG mode is basically the absence of
ARCHIVELOG mode and has the disadvantage of not being able to recover to any
ball in time. NOARCHIVELOG mode does have the advantage of not having to
write transactions to an archive log and thus increases the performance of the
database slightly.
4· What command would you use to create a backup control file?
Alter database backup control file to trace.
5· What is the purpose of the IMPORT option IGNORE? What is its default
setting?
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is
not specified the tables that already exist will be skipped. If it is specified, the
error is ignored and the table’s data will be inserted. The default value is N.
6· You are using hot backup without being in archivelog mode, can you
recover in the event of a failure? Why or why not?
We are unable to take hot backup in noarchive mode. You can’t use hot backup
without being in archivelog mode. So no, you couldn’t recover.
7· How many redo logs should you have and how should they be configured
for maximum recoverability?
You should have at least three groups of two redo logs with the two logs each on
a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw
devices on UNIX if it can be avoided.
8· Users aren’t being allowed on the system. The following message is
received: ORA-00257 archiver is stuck. Connect internal only, until freed :
What is the problem?
The archive destination is probably full, take backup of archivelogs and remove
them . archiver process will re-start.
9· You get a call from you backup DBA while you are on vacation. He has
corrupted all of the control files while playing with the ALTER DATABASE
BACKUP CONTROLFILE command. What do you do?
CONNECT sys as sysdba
STARTUP MOUNT
(Take any read-only tablespaces offline before next step ALTER DATABASE
DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE
ALTER DATABASE OPEN RESETLOGS;
(bring read-only tablespaces back online)
Shutdown and backup the system, then restart
If they have a recent output file from the ALTER DATABASE BACKUP CONTROL
FILE TO TRACE; command, they can use that to recover as well.
If no backup of the control file is available then the following will be required:
CONNECT INTERNAL
STARTUP NOMOUNT
CREATE CONTROL FILE .....;
However, they will need to know all of the datafiles, logfiles, and settings for
MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the
database to use the command.
10· What are the steps involved in Database Startup?
Start an instance, Mount the Database and Open the Database.
11· What are the steps involved in Instance Recovery?
Rolling forward to recover data that has not been recorded in data files yet has
been recorded in the on-line redo log, including the contents of rollback
segments. Rolling back transactions that have been explicitly rolled back or have
not been committed as indicated by the rollback segments regenerated in step a.
Releasing any resources (locks) held by transactions in process at the time of the
failure. Resolving any pending distributed transactions undergoing a two-phase
commit at the time of the instance failure.
12· Can Full Backup be performed when the database is open?
No.
13· What are the steps involved in Database Shutdown?
Close the Database, Dismount the Database and Shutdown the Instance.
14· What is Archived Redo Log?
Archived Redo Log consists of Redo Log files that have archived before being
reused.
15· What is Restricted Mode of Instance Startup?
An instance can be started in (or later altered to be in) restricted mode so that
when the database is open connections are limited only to those whose user
accounts have been granted the RESTRICTED SESSION system privilege
1. Explain the difference between a hot backup and a cold backup and the
benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and
running and it must be in archive log mode. A cold backup is taking a backup of
the database while it is shut down and does not require being in archive log
mode. The benefit of taking a hot backup is that the database is still available for
use while the backup is occurring and you can recover the database to any ball in
time. The benefit of taking a cold backup is that it is typically easier to administer
the backup and recovery process. In addition, since you are taking cold backups
the database does not require being in archive log mode and thus there will be a
slight performance gain as the database is not cutting archive logs to disk.
2· You have just had to restore from backup and do not have any control
files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the
data files where and then issue the recover command with the using backup
control file clause.
3· Explain the difference between ARCHIVELOG mode and NOARCHIVELOG
mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a
backup of all transactions that have occurred in the database so that you can
recover to any ball in time. NOARCHIVELOG mode is basically the absence of
ARCHIVELOG mode and has the disadvantage of not being able to recover to any
ball in time. NOARCHIVELOG mode does have the advantage of not having to
write transactions to an archive log and thus increases the performance of the
database slightly.
4· What command would you use to create a backup control file?
Alter database backup control file to trace.
5· What is the purpose of the IMPORT option IGNORE? What is its default
setting?
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is
not specified the tables that already exist will be skipped. If it is specified, the
error is ignored and the table’s data will be inserted. The default value is N.
6· You are using hot backup without being in archivelog mode, can you
recover in the event of a failure? Why or why not?
We are unable to take hot backup in noarchive mode. You can’t use hot backup
without being in archivelog mode. So no, you couldn’t recover.
7· How many redo logs should you have and how should they be configured
for maximum recoverability?
You should have at least three groups of two redo logs with the two logs each on
a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw
devices on UNIX if it can be avoided.
8· Users aren’t being allowed on the system. The following message is
received: ORA-00257 archiver is stuck. Connect internal only, until freed :
What is the problem?
The archive destination is probably full, take backup of archivelogs and remove
them . archiver process will re-start.
9· You get a call from you backup DBA while you are on vacation. He has
corrupted all of the control files while playing with the ALTER DATABASE
BACKUP CONTROLFILE command. What do you do?
CONNECT sys as sysdba
STARTUP MOUNT
(Take any read-only tablespaces offline before next step ALTER DATABASE
DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE
ALTER DATABASE OPEN RESETLOGS;
(bring read-only tablespaces back online)
Shutdown and backup the system, then restart
If they have a recent output file from the ALTER DATABASE BACKUP CONTROL
FILE TO TRACE; command, they can use that to recover as well.
If no backup of the control file is available then the following will be required:
CONNECT INTERNAL
STARTUP NOMOUNT
CREATE CONTROL FILE .....;
However, they will need to know all of the datafiles, logfiles, and settings for
MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the
database to use the command.
10· What are the steps involved in Database Startup?
Start an instance, Mount the Database and Open the Database.
11· What are the steps involved in Instance Recovery?
Rolling forward to recover data that has not been recorded in data files yet has
been recorded in the on-line redo log, including the contents of rollback
segments. Rolling back transactions that have been explicitly rolled back or have
not been committed as indicated by the rollback segments regenerated in step a.
Releasing any resources (locks) held by transactions in process at the time of the
failure. Resolving any pending distributed transactions undergoing a two-phase
commit at the time of the instance failure.
12· Can Full Backup be performed when the database is open?
No.
13· What are the steps involved in Database Shutdown?
Close the Database, Dismount the Database and Shutdown the Instance.
14· What is Archived Redo Log?
Archived Redo Log consists of Redo Log files that have archived before being
reused.
15· What is Restricted Mode of Instance Startup?
An instance can be started in (or later altered to be in) restricted mode so that
when the database is open connections are limited only to those whose user
accounts have been granted the RESTRICTED SESSION system privilege
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