[bbk5373] 第88集 -第11章 -数据库诊断 04

What is blokc corruption?

• Whenver a block is read or written,a consistency check is performed.
  • Block version
  • DBA(data block address) value in cache as compared to the DBA value in the block buffer
  • Blcok-checjsum,if enabled
• A corrupt block is identified as being one of the following:
  • Media corrupt
  • Logically(or software) corrupt

Block Corruption Symptoms:ORA-01578

The error ORA-01578:"ORACLE data block corrupted(file # %s,block # %s)":

• Is generated when a corrupted data block is found
• Always returns the relative file number and block number
• Is returned to the session that issued the query being performed when the corruption was discovered
• Appears in the alert.log file

How to Handle Corruption

• Check the alert log and operating system log file.
• Use available diagnostic tools to find out the type of corruption
• Determine whether the error persists by running checks multiple times.
• Recover data from the corrupted object if necessary.
• Resolve any hardware issues:
  • Memory boards
  • Disk controllers
  • Disks
• Recover or resotre data from the corrupt object if necessary.

Setting Parametes to Detect Corruption

对于数据库block的损坏情况检查，需要开启一个参数设置，才可以

SQL> show parameter db_block_checking

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_block_checking                    string      FALSE

 

对于系统表空间的数据块，不管是否启用db_block_checking参数，都是要检查的；对于非系统表空间的数据块，则是需要开启此参数，才开始检查的.

注意:在Oracle 11g以前，如果要开启block损坏检查，需要设置三个参数db_block_checking、db_block_checksum、db_lost_wite_protect,11g以后，只需要设置一个参数即可:db_ultra_safe.