I mentioned the PEEKED_BINDS format parameter here, but oddly in the example at the end of the article the bind variable values did not display:
http://hoopercharles.wordpress.com/2010/03/01/dbms_xplan-format-parameters/

Jonathan Lewis also covered the topic, including a couple of different ways to examine bind variable values used in SQL statements:
http://jonathanlewis.wordpress.com/2008/07/24/bind-capture/

One of those methods involves querying V$SQL_BIND_DATA, which according to the documentation, will only show the bind variables submitted by the current session for SQL statements executed by the current session:
http://download.oracle.com/docs/cd/E14072_01/server.112/e10820/dynviews_3044.htm

Excellent work as usual. There is an option to the DISPLAY_CURSOR format parameter that allows you to display the peeked bind variables. So your command would look like:

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST +PEEKED_BINDS'));

Here is the output from your first run with the +PEEKED_BINDS option:

SQL > VARIABLE N1 NUMBER
SQL > EXEC :N1:=2

PL/SQL procedure successfully completed.

SQL > SELECT /*+ GATHER_PLAN_STATISTICS */
  2    C1,
  3    C2
  4  FROM
  5    T1
  6  WHERE
  7    C2 = :N1;

no rows selected

SQL > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST +PEEKED_BINDS'));

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------------------------------

SQL_ID  c7su63uw7nch6, child number 0
-------------------------------------
SELECT /*+ GATHER_PLAN_STATISTICS */   C1,   C2 FROM   T1 WHERE   C2 =
:N1

Plan hash value: 236868917

------------------------------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |
------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |      1 |        |      0 |00:00:00.01 |       3 |   1 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T1        |      1 |   4322 |      0 |00:00:00.01 |       3 |   1 |
|*  2 |   INDEX RANGE SCAN          | IND_T1_C2 |      1 |   4322 |      0 |00:00:00.01 |       3 |   1 |
------------------------------------------------------------------------------------------------------------

Peeked Binds (identified by position):
--------------------------------------

   1 - (NUMBER): 2

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

   2 - access("C2"=:N1)

Now running with this:

SQL > VARIABLE N1 NUMBER
SQL > EXEC :N1:=99</code>

We see:

<code>SQL > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ALLSTATS LAST +PEEKED_BINDS'));

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------

SQL_ID  c7su63uw7nch6, child number 0
-------------------------------------
SELECT /*+ GATHER_PLAN_STATISTICS */   C1,   C2 FROM   T1 WHERE   C2 =
:N1

Plan hash value: 236868917

------------------------------------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Starts | E-Rows | A-Rows |   A-Time   | Buffers | Reads  |
------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |      1 |        |  10000 |00:00:00.06 |    1781 |  86 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T1        |      1 |   4322 |  10000 |00:00:00.06 |    1781 |  86 |
|*  2 |   INDEX RANGE SCAN          | IND_T1_C2 |      1 |   4322 |  10000 |00:00:00.04 |     690 |   0 |
------------------------------------------------------------------------------------------------------------

Peeked Binds (identified by position):
--------------------------------------

   1 - (NUMBER): 2

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

   2 - access("C2"=:N1)

We still see that the peeked value has not changed at all. I think this new section in the execution plan helps further illustrate this point.

This was all run from an 11.2.0.2 environment.

What a perfect timing! I was working on part-2 of my “Everything you want to know about Oracle Histogram” series and then yesterday I found your post.

Anyway, it’s very well written and left no scope of improvement for me!

Appreciate your good work.

Cheers, Neeraj