hint OPAQUE_TRANSFORM產生的原因

在AWR報告中經常看到一個hint /*+ OPAQUE_TRANSFORM */,感到莫名其妙。原因是什麼引起的呢？如果在資料庫B的AWR中看到這種hint,原因是其他資料庫通過DB link訪問資料庫B，且用的是insert into table_name select * from table_name@dblink_name的方式訪問。

SQL> explain plan for insert into test select * from REMOTE_SMALL_TAB@DBLINK_TEST;

已解釋。

SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------------
Plan hash value: 1788691278
-----------------------------------------------------------------------------------------------------
| Id  | Operation        | Name            | Rows  | Bytes | Cost (%CPU)| Time    | Inst  |IN-OUT|
-----------------------------------------------------------------------------------------------------
|  0 | INSERT STATEMENT |                  | 72229 |  6842K|  186  (1)| 00:00:03 |        |      |
|  1 |  REMOTE          | REMOTE_SMALL_TAB | 72229 |  6842K|  186  (1)| 00:00:03 | DBLIN~ | R->S |
-----------------------------------------------------------------------------------------------------
Remote SQL Information (identified by operation id):
----------------------------------------------------
  1 - SELECT /*+ OPAQUE_TRANSFORM */ "OWNER","OBJECT_NAME","SUBOBJECT_NAME","OBJECT_ID","DAT
      A_OBJECT_ID","OBJECT_TYPE","CREATED","LAST_DDL_TIME","TIMESTAMP","STATUS","TEMPORARY","GENERA
      TED","SECONDARY","NAMESPACE","EDITION_NAME" FROM "REMOTE_SMALL_TAB" "REMOTE_SMALL_TAB"
      (accessing 'DBLINK_TEST.EYGLE.COM' )
已選擇17行。

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