【Oracle】SQL优化的重要工具--AUTOTRACE

【AUTOTRACE】SQL优化的重要工具--AUTOTRACE

提到SQL优化，不能不提AUTOTRACE的强大功能。使用起来非常便捷，不过在是使用之前，需要做一些配置的工作。简要的描述一下这个过程，供没有使用过的朋友参考。

1.使用sys用户执行plustrce脚本
sys@ora10g> @?/sqlplus/admin/plustrce
sys@ora10g> drop role plustrace;
drop role plustrace
          *
ERROR at line 1:
ORA-01919: role 'PLUSTRACE' does not exist


sys@ora10g> create role plustrace;

Role created.

sys@ora10g> grant select on v_$sesstat to plustrace;

Grant succeeded.

sys@ora10g> grant select on v_$statname to plustrace;

Grant succeeded.

sys@ora10g> grant select on v_$mystat to plustrace;

Grant succeeded.

sys@ora10g> grant plustrace to dba with admin option;

Grant succeeded.

sys@ora10g> set echo off

2.将plustrace授权给public用户，以便保证所有用户都有权使用autotrace功能
sys@ora10g> grant plustrace to public;

Grant succeeded.

3.连接到具体的用户中，这里是sec用户
sys@ora10g> conn sec/sec
Connected.

4.使用“set autotrace”查看autotrace的命令提示
sec@ora10g> set autotrace
Usage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]]

5.这里演示一种设置方法
sec@ora10g> set autotrace traceonly
sec@ora10g> select * from cat;

20 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 3442307057

--------------------------------------------------------------------------------
| Id  | Operation             | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |        |   646 | 47804 |    33   (4)| 00:00:01 |
|*  1 |  FILTER               |        |       |       |            |          |
|*  2 |   TABLE ACCESS FULL   | OBJ$   |  1324 | 97976 |    33   (4)| 00:00:01 |
|*  3 |   TABLE ACCESS CLUSTER| TAB$   |     1 |    12 |     2   (0)| 00:00:01 |
|*  4 |    INDEX UNIQUE SCAN  | I_OBJ# |     1 |       |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------

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

   1 - filter("O"."TYPE#"=4 OR "O"."TYPE#"=5 OR "O"."TYPE#"=6 OR
              "O"."TYPE#"=2 AND  NOT EXISTS (SELECT /*+ */ 0 FROM "SYS"."TAB$" "T"
              WHERE "T"."OBJ#"=:B1 AND (BITAND("T"."PROPERTY",512)=512 OR
              BITAND("T"."PROPERTY",8192)=8192)))
   2 - filter("O"."OWNER#"=USERENV('SCHEMAID') AND "O"."LINKNAME" IS
              NULL)
   3 - filter(BITAND("T"."PROPERTY",512)=512 OR
              BITAND("T"."PROPERTY",8192)=8192)
   4 - access("T"."OBJ#"=:B1)


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

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