Backup and Recovery FAQ

1. What is retention policy?
2. RMAN has the following advantages over Traditional backups?
3. What are the use of VALIDATE in RMAN?
4. What is Incremental backup?
5.What happens during oracle database hot backup?

1. What is retention policy?
Retention policy describes which backups will be kept and for how long
There are 2 types of retention policies

Recovery Window:
Establishes a period of time within which point-in-time-recovery must be possible

Redundancy:
Establishes a fixed number of backups that must be kept

2. RMAN has the following advantages over Traditional backups?

1. Ability to perform INCREMENTAL block-level backups and block-level media recovery
2. Detect corrupted blocks during backup.
3. Use binary compression when creating backups.
4. You can store frequently executed operations as scripts in the database.
5. RMAN operations can be intergrated with oracle database scheduler to automate backup operations.
6. RMAN provides performance enhancements such as;
(a). Automatic parallelization of backup, restore and recovery operations.
(b). No generation of extra redo during online database backups.
(c). Tape streaming.
7. Ability to automatically backup CONTROLFILE and SPFILE.

3. What are the use of VALIDATE in RMAN?

The main purpose of RMAN validation is to check for corrupt blocks and missing files.
To examine a backup set and report whether it can be restored.
RMAN scans all of the backup pieces in the specified backup sets and looks at the checksums
to verify that the contents are intact so that the backup can be successfully restored if necessary.

VALIDATE BACKUPSET 218;

4. What is Incremental backup?

An Incremental backup is either a level 0, which includes every block in the datafile except block that have never been used
or level 1 backups. Which includes only those blocks that have changed since a previous backup was taken.

There are 2 types of incremental backup
1. Differential incremental backup:
The default type of incremental backup that backup all blocks from most recent incremental at either level 1 or level 0.

2.Cumulative incremental backup:
Backup all blocks from most recent incremental at level 0

Comparison between differential and cumulative incremental backup?

1. Differential incremenatl backups are faster, write out fewer blocks, and produce smaller backup files.
But recovery is slow because during recovery, RMAN has to retrieve each incremental backup and apply it.

2. Cumulative incremental backups may take longer, write out more blocks, and produce larger baclup files.
Cumulative are backup provided for recovery speed because fewer backups must be applied when recovering.

RMAN>backup incremental level 2 cumulative database;

5.What happens during oracle database hot backup?

1.) The corresponding tablespace is checkpointed
2.) The checkpoint SCN marker in the datafile headers cause to increment with checkpoints.
3.) Full images of changed DB blocks are written to the redologs.
Whenever you issue,
ALTER TABLESPACE tbs_name BEGIN BACKUP;

At that point a checkpoint is performed against the target tablespace and
The datafile header is frozen, so no more updates are allowed on it
But during backup process, the corresponding datafiles in the tablespace allow just normal read/write operations,
that is I/O activity is not frozen.

In case of redo log generation, each block will be recorded into the redo log files.

5. What is a data pump?

Datapump is new utility in oracle10g. This is similar to exp/imp. Though exp/imp is available in oracle10g,
Oracle introduced datapump utility with new features. It is more faster than exp. It is more secure than imp/exp.
It provides high speed, parallel, bulk data and metadata movement of Oracle database contents.
In datapump utilities are expdp and impdp. Monitored through dba_datapump_jobs.

6. Lists all datafiles created in the last three days that are not backed up

RMAN> report need backup days 2;

7. To see what datafiles/tablespaces haven’t been backed up in the last 3 days use:

RMAN> report need backup days=3;

8. To see objects which have been created with options like UNRECOVERABLE (for reasons of speed) and have not been backed up yet use:

RMAN> report unrecoverable;

9. shows you your database using rman command

RMAN> report schema;

10. To see the controlfiles backed up and available for recovery

RMAN> list backup of controlfile;

11. To see the SPFILE backup, which is done automatically with the controlfile if you have set CONTROLFILE AUTOBACKUP ON.

RMAN> list backup of spfile;

12. To see backups eligible for recovery which have status AVAILABLE use:

RMAN> list recoverable backup of database;

13. How to identify the Tablespace names from the EXPDP dump file ?

Use the sqlfile option present in impdp utility. This option will write all the SQL DDL to a specified file instead of executing them.
 impdp schemas=scott  sqlfile=scott_sql.txt   directory=test_dir    dumpfile=scott.DMP

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