Tuesday, May 5, 2009
DBA Questions
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What is a Cold Backup
Answer: Cold backup also referred to as an offline backup, is the backup performed while the database is in a cold state ( No Activity ). To ensure consistency in the backup, the database needs to be shutdown while perfoming this kind of backup.
Datafiles, Control Files, Redo Log Files and Parameter Files must be copied to offline storage using the copy utility.
What is the difference between logical and physical backups?
Answer: Logical backup means backing up the individual database objects such as tables, views , indexes.. using the utility called EXPORT, provided by Oracle. The objects exported in this way can be imported into either same database or into any other database. The backed-up copy of information is stored in a dumpfile, and this file can be read using another utility called IMPORT. There is no other way you can use this file.
Physical backups rely on the Operating System to make a copy of the physical files like data files, log files, control files that comprise the database.
How do I find the database archive log status
Answer: Invoke svrmgrl and issuse the following command
ARCHIVE LOG LIST Why does oracle provide Ocopyxx, instead of using copy utility on NT for online backups
Answer: NT copy utility locks the file to prevent access to the file while it is being copied.
Ocopy opens the file using CreateFile() with the FILE_SHARE_READ and FILE_SHARE_WRITE flags. This allows for online backups to be performed and archived redo logs are used for recovering from inconsistencies during backup
Which is better to use, logical backup or physical backup?
Answer: Physical backups are always the best to use because of the ease in restoring and recovering databases from failures.
Logical Backups should be used in conjunction with physical backups to provide redundancy and ease of recovery in case any data is corrupted or objects are dropped due to user errors
Question: Is there a way to read the contents of redo log files and control files?
Answer: NO and Yes
You should not be opening redo logs or control files for reading. Thats the No answer.
Oracle starting with 8i provides a tool called the Log Miner which can be used to extract the do and undo sql for individual transactions from the redo logs.
There is a very good article written by Biju Thomas and you can find the link in the Technical Docs Section of this site.
What is the difference between recovering and restoring?
Answer: Restoring involves copying (most likely from tape) a backup file to replace a damaged datafile. Recovery is the process of applying redo logs to the database to roll it forward.
In case of a datafile loss, you would first restore the datafile from your backup system and then recover the database.
hat are the best backup plan and quick recovery ?
Answer: this is a environment specific solution....
(Tim Cheng Writes ...)
Our production DB is 7 x 24 for telcom company.And we need backup 300+ Gb and
quick recovery when the storage failures.
Our backup plan are below:
1. enable archive mode
2. put addition redo members to another storage.
3 hot backup for all data files to another storage (We take 5 hours for 300+ Gb every day)
4. logical backup for all db structure & important tables.
5 setup a standby DB on another server for contingency
6 select OPS(Oracle Parallel Server) option
what is incrementa export or incremental backup
and how to do it.
i am using oracle8 in sun solaris platform
Answer: An incremental export is an export taken since the last full or cumulative export. The incremental export only exports the objects ( ex : tables ) that have changed since the last full or cumulative export.
An incremental backup acts at a DATA BLOCK level when performed with RMAN. This makes the database backups a lot smaller when there are minor changes to a large database. Only changed blocks since the last backup are written to the backup set.
This post was written by: Franklin Manuel
Franklin Manuel is a professional blogger, web designer and front end web developer. Follow him on Twitter
2 Responses to “DBA Questions”
July 8, 2011 at 4:43 AM
hi
July 9, 2011 at 3:59 AM
This one is a very supporting post for all the students who do wanted to become a DBA. These are the main questions that are being asked in an interview. Well my aim is also to be in database field and so to make my dream come true I love to read more and more information about database. Thanks for helping out by sharing this useful post.
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