Oracle interview questions-Technology

This article is a collection of questions for Oracle technicians. The answer is for reference only ......

1. Explain the differences between cold backup and hot backup and their respective advantages

Answer: Hot Backup is applicable to databases in the archive mode. When the database is still in the working state, it is backed up. Cold backup refers to the backup after the database is closed, applicable to all databases. Hot Standby
The advantage 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 the cold backup data
The database can work in non-archive mode, and the database performance is slightly better than that in archive mode. (Because archive log is not necessarily written to the 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 file.

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 (the term here is recommended)

A: data block is the smallest logical storage unit in the database. When database objects require more physical storage space, continuous data blocks constitute extent. A database object

All the extents are called the segment of this object.

5. Two Methods of checking table structure are provided.

Answer: 1. Describe command

2. dbms_metadata.get_ddl package

6. How to view database engine errors

Answer: 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

A: quick access to the data block in a table

9. Two types of tables in star schema and their data are given respectively.

Answer: fact tables and dimension tables. fact table contain a large amount of major information, while dimension 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 recreate a parent table without affecting the sub-table?

A: The foreign key of the sub-table is forced to take effect. The parent table is rebuilt and the foreign key is activated.

13. Explain the differences between archive and non-archive modes and their respective advantages and disadvantages

A: In archive mode, you can back up all database 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?

Answer:

Startup nomount-start a database instance

Startup Mount-Database loading

Startup open-Open Database

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, use the explain Plan set statement_id = 'tst1' into plan_table

Run utlxplp. SQL or utlxpls. SQL to check 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.

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?

Answer: oracle_base is the root directory of Oracle, and ORACLE_HOME is an oracle product.

Directory.

21. How to determine the time zone of the database?

Answer: Select dbtimezone from dual;

22. Explains the purpose of setting global_names to true.

A: global_names indicates how to connect to the database. If this parameter is set to true, you must use the same name to connect to the remote database when creating a database connection.

23. How to encrypt PL/SQL programs?

Answer: Wrap

24. Differences between function, procedure, and Package

A: function and procedure are a collection of PL/SQL code, usually to complete a task. Procedure does not need to return any value, and function will return one value to another.

The package is a set of functions and proceudrs to complete a commercial function.

25. Explain the purpose of Table Function

A: The table function returns a set of records through the PL/SQL logic for common tables/views. They are also used in pipeline and ETL processes.

26. Three types of three advisory statistics can be collected.

Answer: buffer cache advice, segment level statistics, timed statistics

27. Which Oracle directory structure does the audit trace store in?

Answer: Unix $ ORACLE_HOME/rdbms/audit windows the Event Viewer

28. Explain the role of materialized views

Answer: materialized views is used to reduce the number of sets of summary, set, and group information. They are generally suitable for data warehouses and DSS systems.

29. Which background process is responsible for clearing a user's process when an error occurs?

Answer: pmon

30. Which background process refreshes materialized views?

A: The Job Queue processes.

31. How can I determine which session is being linked and the resources they are waiting?

Q: V $ session/V $ session_wait

32. description of what is redo logs

A: redo logs is the physical and logical structure used to store database data changes. It can be used to repair databases.

33. How to force log switch?

Answer: Alter system switch logfile;

34. How can I judge DDL changes?

A: You can use logminer or streams.

35. What does coalescing do?

Answer: coalescing fragment the tablespace for dictionary management, and merge the neighboring small extents into a single large extent.

36. What is the difference between temporary tablespace and permanent tablespace?

A: A temporary tablespace is used for temporary objects, such as sorting structures, and permanent tablespaces is used to store objects with 'true' (such as tables and rollback segments)

37. What is the name of the tablespace automatically created when a database is created?

Answer: System tablespace.

38. When creating a user, what permissions should be granted to the new user before it can be connected to the database.

Answer: connect

39. How to add data files in tablespace?

Answer: Alter tablespace add datafile size

40. How to change the data file size?

Answer: Alter database datafile resize;

41. Which view is used to check the size of the data file?

Answer: dba_data_files

42. Which view is used to determine the remaining space of tablespace?

Answer: dba_free_space

43. How can I determine who has added a record to the table?

Answer: Auditing

44. How to reconstruct the index?

Answer: Alter index rebuild;

45. Explain what is partitioning and its advantages.

A: partition splits large tables and indexes into smaller partitions that are easy to manage.

46. You just compiled a PL/SQL package but reported an error. How can I display the error message?

Answer: Show errors

47. How to collect various table status data?

Answer: Analyze

The analyze command.

48. How to start session-level trace

Answer: dbms_session.set_ SQL _trace

Alter session set SQL _trace = true;

49. Differences between import and SQL * Loader

A: These two oracle tools are used to import data to the database.

The difference is that the import tool can only process the data generated by another oracle tool export.

. SQL * loader can import data sources in different ASCII Formats.

50. 2 files used for network connection?

Answer: tnsnames. ora and sqlnet. ora

The reference answer is for reference only!

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