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這篇文章給大家分享的是有關 Oracle12CR2 查詢轉換之表擴展的示例分析的內容。丸趣 TV 小編覺得挺實用的，因此分享給大家做個參考，一起跟隨丸趣 TV 小編過來看看吧。
表擴展工作原理
表分區使用表擴展成為可能。如果在一個分區表上創建一個本地索引，那么優化器可能會標記索引對于特定的分區不可使用。實際有些分區沒有創建索引。在表擴展中，優化器將查詢轉換為一個 union all 語句，讓一些子查詢訪問創建索引的分區，一些子查詢訪問沒有創建索引的分區。優化器可以為每個分區選擇最有效的訪問路徑，而不管它是否存在于查詢所要訪問的所有分區中。
優化器不總是會選擇表擴展
. 表擴展是基于成本
當數據庫訪問擴展表的每個分區只會跨越 union all 的所有分支一次，數據庫所連接的任何表都是在分支中被訪問。
. 語義問題可能導致表擴展無效
例如，一個表出現在一個外連接的右邊對于表擴展來說是無效的。
可以使用 expand_table hint 來控制表擴展。這個 hint 會覆蓋基于成本的決策，但不會覆蓋語義檢查。
表擴展使用場景
優化器基于查詢中出現的謂詞條件對每個表必須被訪問的分區保持跟蹤。分區裁剪能讓優化器使用表擴展來生成更有效的執行計劃。
下面的例子假設滿足以下條件:
. 想要對 sh.sales 表執行星型查詢，表 sh.sales 是基于 time_id 列進行范圍分區的一個分區表。
. 想要禁用特定分區上的索引來查看表擴展的優點。
操作步驟如下:
1. 以 sh 用戶登錄數據庫
[oracle@jytest1 ~]$ sqlplus sh/*****@jypdb
SQL*Plus: Release 12.2.0.1.0 Production on Wed Oct 31 18:09:54 2018
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Last Successful login time: Wed Oct 24 2018 17:00:11 +08:00
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
SQL2. 執行以下查詢
SQL select * from sales where time_id = to_date(2000-01-01 00:00:00 , syyyy-mm-dd hh34:mi:ss) and prod_id = 38;
...........
38 2470 24-DEC-01 2 999 1 31.47
38 13440 24-DEC-01 2 999 1 31.47
38 490 28-DEC-01 2 999 1 31.47
38 8406 28-DEC-01 2 999 1 31.47
38 1466 31-DEC-01 3 351 1 31.47
38 4340 31-DEC-01 3 351 1 31.47
38 10658 31-DEC-01 3 351 1 31.47
38 11390 31-DEC-01 3 351 1 31.47
38 23226 31-DEC-01 3 351 1 31.47
4224 rows selected.3. 查詢執行計劃
SQL select * from table(dbms_xplan.display_cursor(null,null, advanced allstats last runstats_last peeked_binds
SQL_ID 214qgysqqz0k8, child number 0
-------------------------------------
select * from sales where time_id = to_date( 2000-01-01 00:00:00 ,
syyyy-mm-dd hh34:mi:ss ) and prod_id = 38
Plan hash value: 2342444420
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | Pstart| Pstop | A-Rows | A-Time | Buffers |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 224 (100)| | | | 4224 |00:00:00.03 | 334 |
| 1 | PARTITION RANGE ITERATOR | | 1 | 5078 | 143K| 224 (0)| 00:00:01 | 13 | 28 | 4224 |00:00:00.03 | 334 |
| 2 | TABLE ACCESS BY LOCAL INDEX ROWID BATCHED| SALES | 16 | 5078 | 143K| 224 (0)| 00:00:01 | 13 | 28 | 4224 |00:00:00.02 | 334 |
| 3 | BITMAP CONVERSION TO ROWIDS | | 8 | | | | | | | 4224 |00:00:00.01 | 24 |
|* 4 | BITMAP INDEX SINGLE VALUE | SALES_PROD_BIX | 8 | | | | | 13 | 28 | 8 |00:00:00.01 | 24 |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / SALES@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE(12.2.0.1)
DB_VERSION(12.2.0.1)
ALL_ROWS
NO_PARALLEL
OUTLINE_LEAF(@ SEL$1)
BITMAP_TREE(@ SEL$1 SALES @ SEL$1 AND(( SALES . PROD_ID)))
BATCH_TABLE_ACCESS_BY_ROWID(@ SEL$1 SALES @ SEL$1)
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access(PROD_ID =38)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
2 - PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
3 - SALES .ROWID[ROWID,10], PROD_ID [NUMBER,22]
4 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], PROD_ID [NUMBER,22]
-----
- automatic DOP: Computed Degree of Parallelism is 1 because of parallel threshold
58 rows selected.在執行計劃中的 Pstart 與 Pstop 列，顯示了優化器判斷只需要訪問表的 13 到 28 分區。在優化器已經判斷了被訪問的分區之后，它將考慮所有這些分區上可以使用的索引。在上面的執行計劃中，優化器選擇使用 sales_prod_bix 位圖索引
4. 禁用 sales 表中 sales_1995 分區上的索引;
SQL alter index sales_prod_bix modify partition sales_1995 unusable;
Index altered.5. 再次執行之前的查詢語句，然后顯示執行計劃，可以看到執行計劃變成了由兩個子查詢組成的 union all 語句，第一個子查詢還是對 13-28 分區使用索引，第二個子查詢步驟對應的 Pstart 與 Pstop 為 invalid，id=11 的過濾條件為”PROD_ID”=38,id= 9 的過濾條件為”SALES”.”TIME_ID”=TO_DATE(‘2000-01-01 00:00:00 ,‘syyyy-mm-dd hh34:mi:ss))) 這個過濾條件是為否的，所以過濾后的記錄為 0，從對應的 A -Rows 列也可以看到記錄為 0
SQL select * from table(dbms_xplan.display_cursor(null,null, advanced allstats last runstats_last peeked_binds
SQL_ID 214qgysqqz0k8, child number 0
-------------------------------------
select * from sales where time_id = to_date(2000-01-01 00:00:00 ,
syyyy-mm-dd hh34:mi:ss ) and prod_id = 38
Plan hash value: 238952339
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | Pstart| Pstop | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 224 (100)| | | | 4224 |00:00:00.05 | 334 |
| 1 | VIEW | VW_TE_2 | 1 | 5079 | 431K| 224 (0)| 00:00:01 | | | 4224 |00:00:00.05 | 334 |
| 2 | UNION-ALL | | 1 | | | | | | | 4224 |00:00:00.05 | 334 |
| 3 | PARTITION RANGE ITERATOR | | 1 | 5078 | 143K| 224 (0)| 00:00:01 | 13 | 28 | 4224 |00:00:00.03 | 334 |
| 4 | TABLE ACCESS BY LOCAL INDEX ROWID BATCHED | SALES | 16 | 5078 | 143K| 224 (0)| 00:00:01 | 13 | 28 | 4224 |00:00:00.02 | 334 |
| 5 | BITMAP CONVERSION TO ROWIDS | | 8 | | | | | | | 4224 |00:00:00.01 | 24 |
|* 6 | BITMAP INDEX SINGLE VALUE | SALES_PROD_BIX | 8 | | | | | 13 | 28 | 8 |00:00:00.01 | 24 |
|* 7 | FILTER | | 1 | | | | | | | 0 |00:00:00.01 | 0 |
| 8 | PARTITION RANGE EMPTY | | 0 | 1 | 29 | 1 (0)| 00:00:01 |INVALID|INVALID| 0 |00:00:00.01 | 0 |
|* 9 | TABLE ACCESS BY LOCAL INDEX ROWID BATCHED| SALES | 0 | 1 | 29 | 1 (0)| 00:00:01 |INVALID|INVALID| 0 |00:00:00.01 | 0 |
| 10 | BITMAP CONVERSION TO ROWIDS | | 0 | | | | | | | 0 |00:00:00.01 | 0 |
|* 11 | BITMAP INDEX SINGLE VALUE | SALES_PROD_BIX | 0 | | | | |INVALID|INVALID| 0 |00:00:00.01 | 0 |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SET$D0A14387 / VW_TE_2@SEL$0A5B0FFE
2 - SET$D0A14387
3 - SET$D0A14387_1
4 - SET$D0A14387_1 / SALES@SEL$1
7 - SET$D0A14387_2
9 - SET$D0A14387_2 / SALES@SEL$1
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE(12.2.0.1)
DB_VERSION(12.2.0.1)
ALL_ROWS
NO_PARALLEL
OUTLINE_LEAF(@ SET$D0A14387_2)
OUTLINE_LEAF(@ SET$D0A14387_1)
OUTLINE_LEAF(@ SET$D0A14387)
EXPAND_TABLE(@ SEL$1 SALES @ SEL$1)
OUTLINE_LEAF(@ SEL$0A5B0FFE)
OUTLINE(@ SET$D0A14387)
EXPAND_TABLE(@ SEL$1 SALES @ SEL$1)
OUTLINE(@ SEL$1)
NO_ACCESS(@ SEL$0A5B0FFE VW_TE_2 @ SEL$0A5B0FFE)
BITMAP_TREE(@ SET$D0A14387_1 SALES @ SEL$1 AND(( SALES . PROD_ID)))
BATCH_TABLE_ACCESS_BY_ROWID(@ SET$D0A14387_1 SALES @ SEL$1)
BITMAP_TREE(@ SET$D0A14387_2 SALES @ SEL$1 AND(( SALES . PROD_ID)))
BATCH_TABLE_ACCESS_BY_ROWID(@ SET$D0A14387_2 SALES @ SEL$1)
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access(PROD_ID =38)
7 - filter(NULL IS NOT NULL)
9 - filter((SALES . TIME_ID =TO_DATE( 2000-01-01 00:00:00 , syyyy-mm-dd
hh34:mi:ss )))
11 - access(PROD_ID =38)
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - ITEM_1 [NUMBER,22], ITEM_2 [NUMBER,22], ITEM_3 [DATE,7], ITEM_4 [NUMBER,22], ITEM_5 [NUMBER,22], ITEM_6 [NUMBER,22], ITEM_7 [NUMBER,22]
2 - STRDEF[22], STRDEF[22], STRDEF[7], STRDEF[22], STRDEF[22], STRDEF[22], STRDEF[22]
3 - SALES . PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
4 - SALES . PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
5 - SALES .ROWID[ROWID,10], SALES . PROD_ID [NUMBER,22]
6 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], SALES . PROD_ID [NUMBER,22]
7 - SALES . PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
8 - SALES . PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
9 - SALES . PROD_ID [NUMBER,22], SALES . CUST_ID [NUMBER,22], SALES . TIME_ID [DATE,7], SALES . CHANNEL_ID [NUMBER,22], SALES . PROMO_ID [NUMBER,22],
SALES . QUANTITY_SOLD [NUMBER,22], SALES . AMOUNT_SOLD [NUMBER,22]
10 - SALES .ROWID[ROWID,10], SALES . PROD_ID [NUMBER,22]
11 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], SALES . PROD_ID [NUMBER,22]
-----
- automatic DOP: Computed Degree of Parallelism is 1 because of parallel threshold
正文完
