数据分布对访问方式的影响

select  count(*)   from F_EVT_SETR_IBPS_RCVSND XX  where "XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') 
AND "XX"."SYS_DATE"<=TO_DATE(' 
              2014-03-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')

---------117369


select  count(*)   from F_EVT_SETR_IBPS_RCVSND XX 
---------1823862


 select owner,blocks from dba_tables where owner='DWF' and table_name='F_EVT_SETR_IBPS_RCVSND';
 --180322


select count(distinct dbms_rowid.rowid_block_number(rowid)) from F_EVT_SETR_IBPS_RCVSND XX
where "XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') 
AND "XX"."SYS_DATE"<=TO_DATE(' 
              2014-03-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')
--19257   


数据比例:6.43519082035812

访问块比例:10.6792293785561


-----查看索引是否有效:
SQL>      select index_name,status  from dba_indexes
     where table_name='F_EVT_SETR_IBPS_RCVSND';  2  

INDEX_NAME		       STATUS
------------------------------ --------
SYS_C0036386		       VALID
F_EVT_SETR_IBPS_RCVSND_IDX1    VALID

------查看选择性:
SQL>  select a.column_name,
           b.num_rows,
           a.num_distinct Cardinality,
            round(a.num_distinct / b.num_rows * 100, 2) selectivity,
           a.histogram,
          a.num_buckets
      from dba_tab_col_statistics a, dba_tables b
     where a.owner = b.owner
       and a.table_name = b.table_name
      and a.owner = 'DWF'
     and a.table_name = 'F_EVT_SETR_IBPS_RCVSND'
     and a.column_name='SYS_DATE'  2    3    4    5    6    7    8    9   10   11   12  
 13  ;

COLUMN_NAME			 NUM_ROWS CARDINALITY SELECTIVITY HISTOGRAM	  NUM_BUCKETS
------------------------------ ---------- ----------- ----------- --------------- -----------
SYS_DATE			  1823862	 1216	      .07 HEIGHT BALANCED	  254

----------查看统计信息是否过期
SQL> select owner, table_name name, object_type, stale_stats, last_analyzed
  from dba_tab_statistics
 where table_name in ('F_EVT_SETR_IBPS_RCVSND')
   and owner = 'DWF'
   and (stale_stats = 'YES' or last_analyzed is null);  2    3    4    5  

no rows selected

---查看采样率
SQL> set linesize 200
SQL> SELECT owner,
       table_name,
       num_rows,
       sample_size,
       trunc(sample_size / num_rows * 100) ectimate_percent
  FROM DBA_TAB_STATISTICS
 where 
    owner = 'DWF'
    and table_name='F_EVT_SETR_IBPS_RCVSND';    2    3    4    5    6    7    8    9  

OWNER			       TABLE_NAME			NUM_ROWS SAMPLE_SIZE ECTIMATE_PERCENT
------------------------------ ------------------------------ ---------- ----------- ----------------
DWF			       F_EVT_SETR_IBPS_RCVSND		 1823862     1823862		  100

---对比执行计划
SQL> explain plan for select *  from F_EVT_SETR_IBPS_RCVSND XX  where "XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') 
AND "XX"."SYS_DATE"<=TO_DATE(' 
              2014-03-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')
  2    3    4  ;

Explained.

SQL> select * from table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1166731381

--------------------------------------------------------------------------------------------
| Id  | Operation	  | Name		   | Rows  | Bytes | Cost (%CPU)| Time	   |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |			   |   122K|	74M| 48895   (1)| 00:09:47 |
|*  1 |  TABLE ACCESS FULL| F_EVT_SETR_IBPS_RCVSND |   122K|	74M| 48895   (1)| 00:09:47 |
--------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd
	      hh24:mi:ss') AND "XX"."SYS_DATE"<=TO_DATE(' 2014-03-31 00:00:00', 'syyyy-mm-dd
	      hh24:mi:ss'))

15 rows selected.

SQL> explain plan for select /*+ index (XX F_EVT_SETR_IBPS_RCVSND_IDX1)*/  *  from F_EVT_SETR_IBPS_RCVSND XX  where "XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') 
AND "XX"."SYS_DATE"<=TO_DATE(' 
              2014-03-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss')  2    3  ;

Explained.

SQL> select * from table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 577873514

-----------------------------------------------------------------------------------------------------------
| Id  | Operation		    | Name			  | Rows  | Bytes | Cost (%CPU)| Time	  |
-----------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	    |				  |   122K|    74M| 58832   (1)| 00:11:46 |
|   1 |  TABLE ACCESS BY INDEX ROWID| F_EVT_SETR_IBPS_RCVSND	  |   122K|    74M| 58832   (1)| 00:11:46 |
|*  2 |   INDEX RANGE SCAN	    | F_EVT_SETR_IBPS_RCVSND_IDX1 |   122K|	  |   327   (1)| 00:00:04 |
-----------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("XX"."SYS_DATE">=TO_DATE(' 2014-03-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND
	      "XX"."SYS_DATE"<=TO_DATE(' 2014-03-31 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))

15 rows selected.