In 11.1.0.6, there appears to be a bug regarding the interaction of Virtual Columns with the ‘row shipping’ enhancement.

Thanks to Miladin Modrakovic for the heads-up on row shipping.
Wide Table Select Row Shipping

SQL*Plus: Release 11.1.0.6.0 - Production on Mon Oct 5 09:26:33 2009
Copyright (c) 1982, 2007, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - 64bit Production
With the Partitioning option

SQL> create table t2_vc
  2  ( col0 varchar2(30) generated always as ('SAMPLE'),
  3    col1 number,
  4    col2 number,
  5    col3 number,
  6    col4 number
  7    );

Table created.

SQL> insert into t2_vc (col1) values (1);

1 row created.

SQL> select * from t2_vc;

COL0        COL1       COL2       COL3       COL4
----- ---------- ---------- ---------- ----------
               1

Note COL0 is incorrectly returned as NULL.

Turn on row shipping notes in the explain plan

SQL> alter session set "_row_shipping_explain" = true;

Session altered.
 
SQL> explain plan for select * from t2_vc;

Explained.
 
SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3599290104
---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |     1 |    69 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T2_VC |     1 |    69 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------
Note
-----
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
   - dynamic sampling used for this statement
   - row shipping is enabled for this statement

13 rows selected.

Virtual columns fail with row shipping enabled. Try again without row shipping:

SQL> alter session set "_enable_row_shipping" = false;

Session altered.

SQL> select * from t2_vc;

COL0        COL1       COL2       COL3       COL4
----- ---------- ---------- ---------- ----------
SAMPLE          1

COL0 is correctly returned.

SQL> explain plan for select * from t2_vc;

Explained.

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3599290104
---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |     1 |    69 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T2_VC |     1 |    69 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------
Note
-----
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
   - dynamic sampling used for this statement

12 rows selected.

Virtual columns now work correctly.
Test the threshold (default is 80%). If we select more than 4 columns from our 5 column table, the threshold is exceeded and row shipping is enabled. Select only 4 columns and row shipping is disabled and everything is fine.

SQL> alter session set "_enable_row_shipping" = true;

Session altered.

SQL> select col0,col1,col2,col3,col4 from t2_vc;

COL0        COL1       COL2       COL3       COL4
----- ---------- ---------- ---------- ----------
               1

Execution Plan
----------------------------------------------------------
Plan hash value: 3599290104
---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |     1 |    69 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T2_VC |     1 |    69 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------
Note
-----
   - dynamic sampling used for this statement
   - row shipping is enabled for this statement

SQL> select col0,col1,col2,col3 from t2_vc;

COL0        COL1       COL2       COL3
----- ---------- ---------- ----------
SAMPLE          1

Execution Plan
----------------------------------------------------------
Plan hash value: 3599290104
---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       |     1 |    56 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T2_VC |     1 |    56 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------
Note
-----
   - dynamic sampling used for this statement

Interestingly, the threshold calculation also seems a bit broken, at least it does the way I interpret it. Even though I’m selecting all columns, if I set the threshold to 81% row shipping is disabled for the virtual column table.

See the following attachment for an example of the threshold seemingly behaving in an unexpected way when virtual columns are involved.

rowship.txt