Reason why hint OPAQUE_TRANSFORM is generated

I often see an hint/* + OPAQUE_TRANSFORM */In the AWR Report, which is inexplicable. Why? If you see this hint in AWR of database B, the reason is that other databases ACCESS database B through DB link, and access using insert into table_name select * from table_name @ dblink_name.

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

Explained.

SQL> select * from table (dbms_xplan.display );
PLAN_TABLE_OUTPUT
Bytes -----------------------------------------------------------------------------------------------------
Plan hash value: 1788691278
Bytes -----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (% CPU) | Time | Inst | IN-OUT |
Bytes -----------------------------------------------------------------------------------------------------
| 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 |
Bytes -----------------------------------------------------------------------------------------------------
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 ')
You have selected 17 rows.

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