索引質量的高低對數據庫整體性能有著直接的影響。良好高質量的索引使得數據庫性能得以數量級別的提升，而低效冗余的索引則使得數據庫性能緩慢如牛，即便是使用高檔的硬件配置。因此對於索引在設計之初需要經過反復的測試與考量。那對於已經置於生產環境中的數據庫，我們也可以通過查詢相關數據字典得到索引的質量的高低，通過這個分析來指導如何改善索引的性能。下面給出了演示以及索引創建的基本指導原則，最後給出了索引質量分析腳本。
1、查看索引質量
--獲取指定schema或表上的索引質量信息報告
gx_adm@CABO3> @idx_quality
Enter value for input_owner: GX_ADM
Enter value for input_tbname: CLIENT_TRADE_TBL -->如果我們省略具體的表名則會輸出整個schema的索引質量報告
Table Table Index Data Blks Leaf Blks Clust Index
Table Rows Blocks Index Size MB per Key per Key Factor Quality
------------------------- ------------ ---------- ------------------------- ------- --------- --------- ------------ -------------
CLIENT_TRADE_TBL 6,318,035 278488 I_TDCL_ARC_STL_DATE_STOCK 62 312 13 171,017 5-Excellent
I_TDCL_ARC_STL_DATE_CASH 62 318 13 174,599 5-Excellent
I_TDCL_ARC_CANCEL_DATE 83 238 8 288,678 5-Excellent
I_TDCL_ARC_INPUT_DATE 144 249 13 310,974 5-Excellent
I_TDCL_ARC_TRADE_DATE 144 269 14 337,097 5-Excellent
PK_CLIENT_TRADE_TBL 200 1 1 798,216 2-Good
I_TDCL_ARC_GRP_REF_ID 144 1 1 811,468 2-Good
UNI_TDCL_ARC_REF_ID 136 1 1 765,603 2-Good
I_TDCL_ARC_CONTRACT_NUM 72 1 1 834,491 2-Good
I_TDCL_ARC_SETTLED_DATE 61 299 5 380,699 1-Poor
I_TDCL_ARC_ACC_NUM 184 624 3 3,899,446 1-Poor
I_TDCL_ARC_PL_STK 176 218 1 4,348,804 1-Poor
I_TDCL_ARC_INSTRU_ID 120 2,667 8 4,273,038 1-Poor
--從上面的單表輸出的索引質量可知，出現了4個處於Poor級別的索引，也就是說這些個索引具有較大的聚簇因子，幾乎接近於表上的行了
--對於這幾個索引的質量還應結合該索引的使用頻率來考量該索引存在的必要性
--對於聚簇因子，只能通過重新組織表上的數據來，以及調整相應索引列的順序得以改善
--查詢單表上索引列的相關信息
gx_adm@CABO3> @idx_info
Enter value for owner: GX_ADM
Enter value for table_name: CLIENT_TRADE_TBL
TABLE_NAME INDEX_NAME CL_NAM CL_POS STATUS IDX_TYP DSCD
------------------------- ------------------------------ -------------------- ------ -------- --------------- ----
CLIENT_TRADE_TBL I_TDCL_ARC_ACC_NUM ACC_NUM 1 VALID NORMAL ASC
I_TDCL_ARC_CANCEL_DATE CANCEL_DATE 1 VALID NORMAL ASC
I_TDCL_ARC_CONTRACT_NUM CONTRACT_NUM 1 VALID NORMAL ASC
I_TDCL_ARC_GRP_REF_ID GRP_REF_ID 1 VALID NORMAL ASC
I_TDCL_ARC_INPUT_DATE INPUT_DATE 1 VALID NORMAL ASC
I_TDCL_ARC_INSTRU_ID INSTRU_ID 1 VALID NORMAL ASC
I_TDCL_ARC_PL_STK STOCK_CD 1 VALID NORMAL ASC
I_TDCL_ARC_PL_STK PL_CD 2 VALID NORMAL ASC
I_TDCL_ARC_SETTLED_DATE SETTLED_DATE 1 VALID NORMAL ASC
I_TDCL_ARC_STL_DATE_CASH STL_DATE_CASH 1 VALID NORMAL ASC
I_TDCL_ARC_STL_DATE_STOCK STL_DATE_STOCK 1 VALID NORMAL ASC
I_TDCL_ARC_TRADE_DATE TRADE_DATE 1 VALID NORMAL ASC
PK_CLIENT_TRADE_TBL BUSINESS_DATE 1 VALID NORMAL ASC
PK_CLIENT_TRADE_TBL REF_ID 2 VALID NORMAL ASC
UNI_TDCL_ARC_REF_ID REF_ID 1 VALID NORMAL ASC
--從上面的查詢結果可知，當前表TRADE_CLIENT_TBL上含有13個索引，應該來說該表索引存在一定冗余。
--大多數情況下，單表上6-7個索引是比較理想的。過多的索引導致過大的資源開銷，以及降低DML性能。
--script name: idx_quality.sql --Author : Leshami --Blog: http://blog.csdn.net/leshami
--index quality retrieval
SET LINESIZE 145
SET PAGESIZE 1000
SET VERIFY OFF
CLEAR COMPUTES
CLEAR BREAKS
BREAK ON table_name ON num_rows ON blocks
COLUMN owner FORMAT a14 HEADING 'Index owner'
COLUMN table_name FORMAT a25 HEADING 'Table'
COLUMN index_name FORMAT a25 HEADING 'Index'
COLUMN num_rows FORMAT 999G999G990 HEADING 'Table|Rows'
COLUMN MB FORMAT 9G990 HEADING 'Index|Size MB'
COLUMN blocks HEADING 'Table|Blocks'
COLUMN num_blocks FORMAT 9G990 HEADING 'Data|Blocks'
COLUMN avg_data_blocks_per_key FORMAT 999G990 HEADING 'Data Blks|per Key'
COLUMN avg_leaf_blocks_per_key FORMAT 999G990 HEADING 'Leaf Blks|per Key'
COLUMN clustering_factor FORMAT 999G999G990 HEADING 'Clust|Factor'
COLUMN Index_Quality FORMAT A13 HEADING 'Index|Quality'
--SPOOL index_quality
SELECT i.table_name,
t.num_rows,
t.blocks,
i.index_name,
o.bytes / 1048576 mb,
i.avg_data_blocks_per_key,
i.avg_leaf_blocks_per_key,
i.clustering_factor,
CASE
WHEN NVL (i.clustering_factor, 0) = 0 THEN '0-No Stats'
WHEN NVL (t.num_rows, 0) = 0 THEN '0-No Stats'
WHEN (ROUND (i.clustering_factor / t.num_rows * 100)) < 6 THEN '5-Excellent'
WHEN (ROUND (i.clustering_factor / t.num_rows * 100)) BETWEEN 7 AND 11 THEN '4-Very Good'
WHEN (ROUND (i.clustering_factor / t.num_rows * 100)) BETWEEN 12 AND 15 THEN '2-Good'
WHEN (ROUND (i.clustering_factor / t.num_rows * 100)) BETWEEN 16 AND 25 THEN '2-Fair'
ELSE '1-Poor'
END
index_quality
FROM dba_indexes i, dba_segments o, dba_tables t
WHERE
-- i.index_name LIKE UPPER ('%&&1%') AND
i.owner = t.owner
AND i.table_name = t.table_name
AND i.owner = o.owner
AND i.index_name = o.segment_name
AND t.owner = UPPER('&input_owner')
AND t.table_name LIKE UPPER('%&input_tbname%')
ORDER BY table_name,
num_rows,
blocks,
index_quality DESC;
--SPOOL OFF;
===========================================================================================
--script name: idx_info.sql
--get the index column information by specified table
set linesize 180
col cl_nam format a20
col table_name format a25
col cl_pos format 9
col idx_typ format a15
SELECT b.table_name,
a.index_name,
a.column_name cl_nam,
a.column_position cl_pos,
b.status,
b.index_type idx_typ,
a.descend dscd
FROM dba_ind_columns a, dba_indexes b
WHERE a.index_name = b.index_name
AND owner = upper('&owner')
AND a.table_name LIKE upper('%&table_name%')
ORDER BY 2, 4;
4、相關參考
