【eygle】Oracle的分割槽表和Local索引建立與維護

idba發表於2008-06-07
Oracle索引
Oracle的分割槽技術在某些條件下可以極大的提高查詢的效能，所以被廣泛採用。
從產品上說，分割槽技術是Oracle企業版中獨立收費的一個元件。

以下是對於分割槽及本地索引的一個示例。

首先根據字典表建立一個測試分割槽表：
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

建立一個Local索引，注意這裡可以將不同分割槽的索引指定建立到不同的表空間：
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割槽表和非分割槽表的查詢效能差異：
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

對於非分割槽表的測試：
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

當增加表分割槽時，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

-The End-

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/1384/viewspace-342939/，如需轉載，請註明出處，否則將追究法律責任。

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