Oracle技术之和分区表相关的一点总结（二）

1.先来看不垮分区访问时的性能对比，这里我们主要关注逻辑度(consistent gets),

由于第一次访问sql存在解析，因此我们对比时都看第二次访问时的情况，

下面的试验对比都是这样...

注意：目前2个表上都没有index

SQL> select * from t1 where object_id<2000;

已选择249984行。

执行计划

----------------------------------------------------------

Plan hash value: 3617692013

--------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

--------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 270K| 20M| 1069 (4)| 00:00:13 |

|* 1 | TABLE ACCESS FULL| T1 | 270K| 20M| 1069 (4)| 00:00:13 |

--------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("OBJECT_ID"<2000)

Note

-----

- dynamic sampling used for this statement

统计信息

----------------------------------------------------------

222 recursive calls

0 db block gets

21446 consistent gets

4719 physical reads

0 redo size

7439711 bytes sent via SQL*Net to client

183700 bytes received via SQL*Net from client

16667 SQL*Net roundtrips to/from client

2 sorts (memory)

0 sorts (disk)

249984 rows processed

SQL> select * from t1 where object_id<2000;

已选择249984行。

执行计划

----------------------------------------------------------

Plan hash value: 3617692013

--------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

--------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 270K| 20M| 1069 (4)| 00:00:13 |

|* 1 | TABLE ACCESS FULL| T1 | 270K| 20M| 1069 (4)| 00:00:13 |

--------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("OBJECT_ID"<2000)

Note

-----

- dynamic sampling used for this statement

统计信息

----------------------------------------------------------

0 recursive calls

0 db block gets

21341 consistent gets

0 physical reads

0 redo size

7439711 bytes sent via SQL*Net to client

183700 bytes received via SQL*Net from client

16667 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

249984 rows processed

SQL> select * from t where object_id<2000;

已选择249984行。

执行计划

----------------------------------------------------------

Plan hash value: 2931986080

--------------------------------------------------------------------------------

---------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

Pstart| Pstop |

--------------------------------------------------------------------------------

---------------

| 0 | SELECT STATEMENT | | 241K| 7063K| 238 (19)| 00:00:03 |

| |

| 1 | PARTITION RANGE SINGLE| | 241K| 7063K| 238 (19)| 00:00:03 |

1 | 1 |

| 2 | TABLE ACCESS FULL | T | 241K| 7063K| 238 (19)| 00:00:03 |

1 | 1 |

--------------------------------------------------------------------------------

---------------

Note

-----

- dynamic sampling used for this statement

统计信息

----------------------------------------------------------

1305 recursive calls

0 db block gets

17770 consistent gets

890 physical reads

0 redo size

7439711 bytes sent via SQL*Net to client

183700 bytes received via SQL*Net from client

16667 SQL*Net roundtrips to/from client

12 sorts (memory)

0 sorts (disk)

249984 rows processed

SQL> select * from t where object_id<2000;

已选择249984行。

执行计划

----------------------------------------------------------

Plan hash value: 2931986080

--------------------------------------------------------------------------------

---------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

Pstart| Pstop |

--------------------------------------------------------------------------------

---------------

| 0 | SELECT STATEMENT | | 241K| 7063K| 238 (19)| 00:00:03 |

| |

| 1 | PARTITION RANGE SINGLE| | 241K| 7063K| 238 (19)| 00:00:03 |

1 | 1 |

| 2 | TABLE ACCESS FULL | T | 241K| 7063K| 238 (19)| 00:00:03 |

1 | 1 |

--------------------------------------------------------------------------------

---------------

Note

-----

- dynamic sampling used for this statement

统计信息

----------------------------------------------------------

0 recursive calls

0 db block gets

17498 consistent gets

0 physical reads

0 redo size

7439711 bytes sent via SQL*Net to client

183700 bytes received via SQL*Net from client

16667 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

249984 rows processed

SQL>

--========================

效果比较明显，很显然是通过访问分区表的性能更好一些，逻辑读21341大于17498，并且都没有发生物理读，

同时我们从执行计划也能看到访问t1时访问的是单个分区(PARTITION RANGE SINGLE),很明显如果我们能把数据

控制在一个分区之内的话那么分区表的性能要好于普通的heap表

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