Oracle interview questions

 

Oracle interview questions-technical knowledge

This may be an article you have been looking forward to. while paying attention to this part of technical questions, please be sure to read personal questions and answers during the interview. The answer here is not comprehensive. These questions can be explained from multiple perspectives. Maybe you don't have to give a full answer during the interview, you only need to answer your questions to familiarize the interview examiner with Oracle concepts.

1. Explain the differences between cold backup and hot backup and their respective advantages: Hot Backup is used to back up a database in archive mode when the database is still working. Cold backup refers to the backup after the database is closed, applicable to all databases. The advantage of hot backup is that the database can still be used during Backup and can be restored to any point in time. The advantage of cold backup is that its backup and recovery operations are quite simple, and because cold backup databases can work in non-archive mode, the database performance will be slightly better than the archive mode. (Because archive is not required
Log written to hard disk)

2. You must use backup to restore the database, but you do not have control files. How can this problem be solved? A: recreate the control file and use the recover command with the backup control file clause to restore the database.

3. How to convert init. ora to spfile? A: Use the create spfile from pfile command.

4. Explain the differences between data block, extent, and segment (we recommend that you use the term here) Answer: data block is the smallest logical storage unit in the database. When database objects require more physical storage space, continuous data blocks constitute extent. All extents owned by a database object are called the segment of this object.

5. provide two methods to check the table structure: 1. Describe command 2. dbms_metadata.get_ddl package

6. How to view the database engine error message: Alert Log.

7. Compare the truncate and delete commands. A: both of them can be used to delete all records in the table. The difference is that truncate is a DDL operation, which moves hwk and does not require rollback segment. Delete is a DML operation, which requires rollback segment and takes a long time.

8. Reasons for using indexes: quick access to the data block in the table

9. the two types of tables in star schema and their respective data solutions are provided: fact tables and dimension tables. fact table contains a large amount of main information, while dime nsion tables stores information about certain attribute descriptions of fact table.

10. What indexes should be created on the fact table? A: bitmap Index)

11. are two related constraints provided? Answer: primary key and foreign key

12. How to re-create a parent table without affecting the sub-table

13. Differences between archive and non-archive modes and their respective advantages and disadvantages answer: Archive Mode means that you can back up all the databases transactions and restore them to any point in time. Non-archive mode, on the contrary, cannot be recovered to any point in time. However, the non-archive mode can slightly improve the database performance.

14. How to Create a backup control file? Answer: Alter database backup control file to trace.

15. How many statuses does the database normally start? Q: startup nomount? C database instance start startup Mount-database load startup open? Open Database C

16. Which column can be used to distinguish between the V $ view and the GV $ view? A: inst_id indicates a specific instance in the cluster environment.

17. How to generate an explain Plan? A: Run utlxplan. SQL. Create a plan table for specific SQL statements. Run utlxplp. SQL or utlxpls. SQL to view the explain Plan

18. How to Increase the buffer cache hit rate? A: When the database is busy, use the buffer cache advisory tool to query v $ db_cache_advice. If necessary, use the alter system set db_cache_size command.

19. How should ORA-01555 respond? A: The specific error message is snapshot too old within rollback Seg. Generally, you can increase the rollback seg to solve the problem. Of course, you also need to check the specific SQL text that causes the error.

20. What is the difference between $ ORACLE_HOME and $ oracle_base? A: oracle_base is the root directory of Oracle and ORACLE_HOME is the directory of Oracle products.