db file scattered read 定位

**现有系统，查看等待事件的时候，头几个有：DB FILE SCATTERED READ 。

DB FILE SCATTERED READ

The db file scattered read wait event is similar to the db file sequential read, except that the session is waiting for a multi-block I/O read request to complete. The db file scattered read waits are associated with full table scans and index fast full scans (FFS) operations. Oracle reads a set of contiguous blocks up to DB_FILE_MULTIBLOCK_READ_COUNT and scatters them into the Buffer Cache.


1. 找出用户下的全表扫描
  select * from v$session_longops where username = 'GSIMS';

  193 rows selected.

2.找出具体的表

SELECT   distinct target FROM   v$session_longops WHERE   username = 'GSIMS' ;

TARGET                                                         
----------------------------------------------------------------
GSIMS.B_CONTRACT_L                                             
GSIMS.B_CONTRACT                                               
GSIMS.S_LOGACTION                                              
GSIMS.B_REPORT_05                                              
GSIMS.B_REPORT_UNION                                           
GSIMS.B_REPORT_08                                              
GSIMS.B_REPORT_09                                              
GSIMS.B_REPORT_04                                              

8 rows selected.


针对这个问题，调整下：

(1). DB_FILE_MULTIBLOCK_READ_COUNT
(2). 调整表扫描