在網上看到eygle寫的一篇關于分區表和本地索引的文章，感覺總結的挺好，特轉了過來。
Oracle的分區技術在某些條件下可以極大的提高查詢的性能，所以被廣泛采用。從產品上說，分區技術是Oracle企業版中獨立收費的一個組件。以下是對于分區及本地索引的一個示例。
首先根據字典表創建一個測試分區表：
SQL> connect eygle/eygle
Connected.
SQL> CREATE TABLE dbobjs
2 (OBJECT_ID NUMBER NOT NULL,
3 OBJECT_NAME varchar2(128),
4 CREATED DATE NOT NULL
5 )
6 PARTITION BY RANGE (CREATED)
7 (PARTITION dbobjs_06 VALUES LESS THAN (TO_DATE('01/01/2007', 'DD/MM/YYYY')),
8 PARTITION dbobjs_07 VALUES LESS THAN (TO_DATE('01/01/2008', 'DD/MM/YYYY')));
Table created.
SQL> COL segment_name for a20
SQL> COL PARTITION_NAME for a20
SQL> SELECT segment_name, partition_name, tablespace_name
2 FROM dba_segments
3 WHERE segment_name = 'DBOBJS';
SEGMENT_NAME PARTITION_NAME TABLESPACE_NAME
-------------------- -------------------- ------------------------------
DBOBJS DBOBJS_06 EYGLE
DBOBJS DBOBJS_07 EYGLE |
創建一個Local索引，注意這里可以將不同分區的索引指定創建到不同的表空間：
SQL> CREATE INDEX dbobjs_idx ON dbobjs (created) LOCAL
2 (PARTITION dbobjs_06 TABLESPACE users,
3 PARTITION dbobjs_07 TABLESPACE users
4 );
Index created. |
這個子句可以進一步調整為類似：
CREATE INDEX dbobjs_idx ON dbobjs (created) LOCAL
(PARTITION dbobjs_06 TABLESPACE users,
PARTITION dbobjs_07 TABLESPACE users
) TABLESPACE users; |
通過統一的tablespace子句為索引指定表空間。
SQL> COL segment_name for a20
SQL> COL PARTITION_NAME for a20
SQL> SELECT segment_name, partition_name, tablespace_name
2 FROM dba_segments
3 WHERE segment_name = 'DBOBJS_IDX';
SEGMENT_NAME PARTITION_NAME TABLESPACE_NAME
-------------------- -------------------- ------------------------------
DBOBJS_IDX DBOBJS_06 USERS
DBOBJS_IDX DBOBJS_07 USERS
SQL> insert into dbobjs
2 select object_id,object_name,created
3 from dba_objects where created
6227 rows created.
SQL> commit;
Commit complete.
SQL> select count(*) from dbobjs partition (DBOBJS_06);
COUNT(*)
----------
6154
SQL> select count(*) from dbobjs partition (dbobjs_07);
COUNT(*)
----------
73 |
我們可以通過查詢來對比一下分區表和非分區表的查詢性能差異：
SQL> set autotrace on
SQL> select count(*) from dbobjs where created < to_date('01/01/2008','dd/mm/yyyy');
COUNT(*)
----------
6227
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE (Cost=1 Card=1 Bytes=9)
1 0 SORT (AGGREGATE)
2 1 PARTITION RANGE (ALL)
3 2 INDEX (RANGE SCAN) OF 'DBOBJS_IDX' (NON-UNIQUE) (Cost=2 Card=8 Bytes=72)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
25 consistent gets
0 physical reads
0 redo size
380 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> select count(*) from dbobjs where created < to_date('01/01/2007','dd/mm/yyyy');
COUNT(*)
----------
6154
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE (Cost=1 Card=1 Bytes=9)
1 0 SORT (AGGREGATE)
2 1 INDEX (RANGE SCAN) OF 'DBOBJS_IDX' (NON-UNIQUE) (Cost=2 Card=4 Bytes=36)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
24 consistent gets
0 physical reads
0 redo size
380 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> select count(distinct(object_name)) from dbobjs where created < to_date('01/01/2007','dd/mm/yyyy');
COUNT(DISTINCT(OBJECT_NAME))
----------------------------
4753
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE (Cost=1 Card=1 Bytes=75)
1 0 SORT (GROUP BY)
2 1 TABLE ACCESS (BY LOCAL INDEX ROWID) OF 'DBOBJS' (Cost=1 Card=4 Bytes=300)
3 2 INDEX (RANGE SCAN) OF 'DBOBJS_IDX' (NON-UNIQUE) (Cost=2 Card=1)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
101 consistent gets
0 physical reads
0 redo size
400 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed |
對于非分區表的測試：
SQL> CREATE TABLE dbobjs2
2 (object_id NUMBER NOT NULL,
3 object_name VARCHAR2(128),
4 created DATE NOT NULL
5 );
Table created.
SQL> CREATE INDEX dbobjs_idx2 ON dbobjs2 (created);
Index created.
SQL> insert into dbobjs2
2 select object_id,object_name,created
3 from dba_objects where created
6227 rows created.
SQL> commit;
Commit complete.
SQL> select count(distinct(object_name)) from dbobjs2 where created < to_date('01/01/2007','dd/mm/yyyy');
COUNT(DISTINCT(OBJECT_NAME))
----------------------------
4753
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE
1 0 SORT (GROUP BY)
2 1 TABLE ACCESS (BY INDEX ROWID) OF 'DBOBJS2'
3 2 INDEX (RANGE SCAN) OF 'DBOBJS_IDX2' (NON-UNIQUE)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
2670 consistent gets
0 physical reads
1332 redo size
400 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processed |
當增加表分區時，LOCAL索引被自動維護：
SQL> ALTER TABLE dbobjs
2 ADD PARTITION dbobjs_08 VALUES LESS THAN (TO_DATE('01/01/2009', 'DD/MM/YYYY'));
Table altered.
SQL> set autotrace off
SQL> COL segment_name for a20
SQL> COL PARTITION_NAME for a20
SQL> SELECT segment_name, partition_name, tablespace_name
2 FROM dba_segments
3 WHERE segment_name = 'DBOBJS_IDX';
SEGMENT_NAME PARTITION_NAME TABLESPACE_NAME
-------------------- -------------------- ------------------------------
DBOBJS_IDX DBOBJS_06 USERS
DBOBJS_IDX DBOBJS_07 USERS
DBOBJS_IDX DBOBJS_08 EYGLE
SQL> SELECT segment_name, partition_name, tablespace_name
2 FROM dba_segments
3 WHERE segment_name = 'DBOBJS';
SEGMENT_NAME PARTITION_NAME TABLESPACE_NAME
-------------------- -------------------- ------------------------------
DBOBJS DBOBJS_06 EYGLE
DBOBJS DBOBJS_07 EYGLE
DBOBJS DBOBJS_08 EYGLE |
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