Oracle Database part interview Topic ___ Database

  1.  explains the differences between cold and hot backups and their benefits    answers: Hot-backed databases for archive mode, backed up while the database is still working. A cold backup is a database that is backed up after the database is closed and applies to all schemas. The advantage of hot backup is that when the backup is in place, the database can still be used and the database can be restored to any point in time. The advantage of a cold backup is that its backup and recovery operations are fairly simple, and because a cold backed up database can work in a non-archive mode, the database performance is slightly better than the archive mode. 　　(Because the Archive log will not be written to the hard drive) 　　2.  you have to use Backup to restore the database, but you do not have control files, how to solve the problem? 　　Answer: Rebuild the control file and restore the database with the recover  command with the backup control file  clause. 　　3.  How to convert Init.ora to SPFile? Answer: Use the create spfile from pfile  command. 4.  explains the difference between data block , extent  and  segment (it is recommended in English terms) to answer: Data block is the smallest logical storage unit in the database. 　　When objects in a database require more physical storage, successive Data block make up the segment of all extents that a database object has, known as that object. extent .  5.  gives two method answers to the checklist structure: 1.DESCRIBE command 2.dbms_metadata. 　　get_ddl  Package 6.  How to view the database engine error answer: Alert log. 7.  comparison truncate and delete  command answers: Both can be used to delete all records in a table. The difference is: Truncate is a DDL operation, it moves HWK, does not need  rollback segment  and delete is a DML operation,  need rollback segment 　　  It takes a long time. 8.  Reasons to use indexes: Quick access to Data blo in tablesCK 9.  gives two types of tables in Star schema and their respective data solutions:fact tables  and dimension tables. fact  The table  contains a large amount of primary information and  dimension tables  holds information about fact table  some of the properties described 10. fact  　　What index do I need to build on the table? Answer: Bitmap index   (bitmap index)
11.  give two kinds of related constraints? Answer: How primary and foreign keys 12. , without affecting the child table, rebuilding a master Table solution: Foreign key enforcement of the child table, rebuilding the master table, activating the foreign key 13.  explain the differences between archive and non-archive mode and their respective pros and Cons: Archiving mode means that you can back up all the data Library  transactions and restores to any point in time. Non-archive mode, on the contrary, cannot be restored to any point in time. 　　However, non-archive mode can bring a little improvement in database performance. 　　14.  How do I build a backup control file? 　　Answer: Alter database backup control file to trace. 　　15.  gives a few state &nbsp of the normal startup of the database;? Answer:startup nomount  database instance start startup mount  database Mount startup open  database open 16.  　　Which column can be used to distinguish between the v$ view and the gv$ view? 　　Solution: inst_id  indicates a specific   instance  in the cluster environment. 　　How does 17.  generate Explain plan? Answer: Run utlxplan.sql.  build plan  table for specific SQL statements, use  explain plan set statement_id =   ' Tst1 '  into plan_table run utlxplp.sql  or  utlxpls.sql see Explain plan 18.  　　How to increase the hit rate of Buffer cache? Answer: When the database is busy, apply the buffer cache advisory  tool, query v$db_cache_advice .  if necessary change, you can use  alter 　 system set db_cache_size  command　How to deal with 19. ora-01555? Answer: The specific error message is that snapshot too old within rollback seg ,  can usually be increased by rollback  SEG to solve the problem. 　　And of course you need to look at the exact SQL text that caused the error. 20.  explain the difference between $oracle_home and $oracle_base? Answer: Oracle_base is the root directory of Oracle, Oracle_home is the directory of Oracle products.