Oracle - SPM固定执行计划(一)

开启另一个窗口B
SQL> set autot trace
SQL> alter session set optimizer_mode = first_rows_10;
SQL> select /*for_test*/ * from test1 where object_id = 1;

Execution Plan
----------------------------------------------------------
Plan hash value: 2214001748

-----------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |    11 |  1056 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST1     |    11 |  1056 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_TEST1 |       |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

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再开启一个窗口C
SQL> select sql_id,sql_text,optimizer_mode,plan_hash_value,child_number from v$sql where sql_text like ‘select /*for_test*/ * from test1%‘;

SQL_ID        SQL_TEXT                                                OPTIMIZER_ PLAN_HASH_VALUE CHILD_NUMBER
------------- ------------------------------------------------------- ---------- --------------- ------------
66a4184u0t6hn select /*for_test*/ * from test1 where object_id = 1    ALL_ROWS        4122059633            0
66a4184u0t6hn select /*for_test*/ * from test1 where object_id = 1    FIRST_ROWS      2214001748            1

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可以看到，因为优化器模式的不同，相同的sql产生了两条截然不同的执行计划
当optimizer_mode = all_rows为全表扫描，当optimizer_mode = first_rows_10为索引扫描

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4. 绑定执行计划

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