COUNT STOPKEY ROWNUM optimization

No COUNT STOPKEY in explain plan:- ROWNUM optimization

Product:- Oracle Server (RDBMS)

Range of versions believed to be affected:-  12.1

confirmed affected:- 1. 11.1.0.7
                                    2. 10.2.0.4

Platforms affected:-         all

So I was doing explain plan for below SQL on database version 11.2.0.1.0:-

select * from test where rownum = 0;

no rows selected


Execution Plan
----------------------------------------------------------
Plan hash value: 1829668517

-------------------------------------------------------------------------------------
| Id  | Operation           | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |               |  3219K|   733M| 35580   (2)| 00:07:07 |
|   1 |  COUNT              |               |       |       |            |          |
|*  2 |   FILTER            |               |       |       |            |          |
|   3 |    TABLE ACCESS FULL| TEST          |  3219K|   733M| 35580   (2)| 00:07:07 |
-------------------------------------------------------------------------------------

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

   2 - filter(ROWNUM=0)


Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
     129363  consistent gets
     129358  physical reads
          0  redo size
       6210  bytes sent via SQL*Net to client
        513  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed

On Database version 11.2.0.4.0 it was:-

no rows selected


Execution Plan
----------------------------------------------------------
Plan hash value: 2416982823

------------------------------------------------------------------------------------
| Id  | Operation          | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |               |     1 |   240 |     2   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY     |               |       |       |            |          |
|   2 |   TABLE ACCESS FULL| TEST            |     1 |   240 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------------

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

   1 - filter(ROWNUM=0)


Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          0  consistent gets
          0  physical reads
          0  redo size
       6210  bytes sent via SQL*Net to client
        513  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed

After studying on oracle support I found this as a bug on 11.2.0.1.0 explained under Oracle
Please check your version for the bug because you can easily see the difference and performance matrix between both explain plans.

Beware! This use of rownum< can cause performance problems. Using rownum may change the all_rows optimizer mode for a query to first_rows, causing unexpected sub-optimal execution plans. One solution is to always include an all_rows hint when using rownum to perform a top-n query.

Keep sharing :)

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example.dat:
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00009,lmn,
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