SAP DATABASE INTERVIEW QUESTIONS & ANSWERS -1
(Q) what is the size of oracle data block ?
(A) 8 KB (fixed size)
(Q) What are the situations in which DBWO writes dirty blocks to disks ?
(A) If the number of scanned buffers reaches a certain thresh hold.
At a specific time that is when check point occurs.
(Q) What are the conditions in which log writer writes redo log buffer data to online redo log files ?
(A) There 4 conditions:
When transaction is committed.
For every three seconds.
When redo log is 1/3rd of full.
When DBWR is about to write modified buffers to disk and some of the corresponding redo records have not at been written to online redo log i.e. write ahead logging.
(Q)What are the entries in co files ?
(A) Physical structure of database
State of database
Table space information
Names and location of data files and redo log files.
Current log sequence number
(Q) Why do I need ‘SPFILE<SID>.ora’ even though I have ‘init<SID>.ora ?
(A) From Oracle 9.i ‘init<SID>.ora’ is replaced by ‘SPfile<SID>.ora or ‘SPfile.ora.
(Q) If a file is missing from the chain of offline Redo log files, then what we’ll do ?
(A) We have to perform a restore and recovery of Database. Recovery is performed using the method “Point In Time” by which all the Offline Redo log files older than the last one is used for recovery.
(Q) What are the causes for logical errors related to Database ?
(A) (i) Manually deleting parts of Database objects such as Rows in a table.
(ii) Manually dropping Database Objects.
(iii) Manually dropping Application Objects.
(Q) Is Point in Time Recovery a standard Solution for logical errors in production system ?
(Q) Where do we use the Point IN Time Recovery ?
(A) Point in Time is very critical in a system landscape with Data Dependencies between Systems.
(Q) How do we verify Consistency of Oracle Database ?
(A) By performing by a logical data check.
(Q) Why do we need to perform a logical check ?
(A) In order to verify corrupted Data blocks (Ora – 1578)
(Q) Why do we need to perform a physical Data check ?
(A) To verify the tapes used for Database backup.
(Q) How often we perform Online Backup and Offline Backups ?
(A) Online Backup = Daily
Offline Backup = Once in a Week
(Q) How do we perform Backup of Offline Redo log files ?
(A) (i) Backup of every Offline Redo log files is taken TWICE on separate tapes before the files are deleted from Archive Directory.
(ii) Perform additional Backups after each system upgrade and also if Database structure is Modified.
(Q) What are the tools used by Oracle Admin in an SAP System for Backups ?
(A) Database Backups = BRBACKUP
Offline Redo log files = BRARCHIVE
(Q) What are the occasions in which changes to Tile Structure of Database is made ?
(A) 1) When a Data file is added
2) When a Data file is moved to a Different Location.
3) When a Table Space and its Data files are reorganized.
(Q) What are the various Backup types ?
(A) There are 5 Backup types
1) Online Backup
2) Offline Backup
3) Complete Backup
4) Incremental Backup
5) Partial Backup
(Q) If the Corresponding Full Backup is already overwritten and can I use Incremental Backup ?
(A) NO, Incremental Backup is useless.
(Q) Can I perform a Backup of Individual data files using Incremental Backups ?
(Q) What are the various Backup strategies used in SAP ?
(A) There are 3 Backup strategies in SAP
i) Complete Backup:- Restore missing Database files from complete Backup, Restore Offline Redo Log files writte during and after this Backup.
ii) Incremental Backup:- Restore missing Data files from last Full Backup, update them with restore from last Incremental Backup.
iii)Partial Backup:- Replace complete backup with partial Backups , we need a longer time to perform a recovery from media crash.