通过设置SQLPLUS ARRAYSIZE(行预取)加快SQL返回速度

通过设置SQLPLUS ARRAYSIZE(行预取)加快SQL返回速度

有时候你可能会用SQLPLUS spool 表的数据，那么怎么加快spool速度呢？SQLPLUS中有个行预取的选项

SQLPLUS中 arraysize默认为15 

SQL> show arraysize
arraysize 15

它表示从Oracle服务器端一次只传递15行记录到客户端(SQLPLUS)，当然了JDBC,WEBLOGIC也有行预取，具体自己Google

举个例子：

SQL> select * from test where owner='ADWU_OPTIMA_AP11';

773 rows selected.

Elapsed: 00:00:30.95

Execution Plan
----------------------------------------------------------
Plan hash value: 217508114

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |   593 |   134K|   882   (3)| 00:00:03 |
|*  1 |  TABLE ACCESS FULL| TEST |   593 |   134K|   882   (3)| 00:00:03 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("OWNER"='ADWU_OPTIMA_AP11')

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       2976  consistent gets
          0  physical reads
          0  redo size
      50484  bytes sent via SQL*Net to client
        597  bytes received via SQL*Net from client
         53  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        773  rows processed

SQL> set arraysize 5000
SQL> select * from test where owner='ADWU_OPTIMA_AP11';

773 rows selected.

Elapsed: 00:00:16.06

Execution Plan
----------------------------------------------------------
Plan hash value: 217508114

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |   593 |   134K|   882   (3)| 00:00:03 |
|*  1 |  TABLE ACCESS FULL| TEST |   593 |   134K|   882   (3)| 00:00:03 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("OWNER"='ADWU_OPTIMA_AP11')

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       2927  consistent gets
          0  physical reads
          0  redo size
      47800  bytes sent via SQL*Net to client
        241  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        773  rows processed

当设置 arraysize 之后，SQLPLUS 客户端与数据库Server端交互次数明显减少，这就是为什么返回773行数据第二次比第一次快1倍了，同时也可以看到，第二次逻辑读比第一次低了，那说明设置行预取会影响逻辑读。