SELECT
       COUNT (SOURCE)
  FROM (SELECT /*+ full(source$) */
               SOURCE
          FROM sys.source$
        UNION ALL
        SELECT /*+ full(source$) */
               SOURCE
          FROM sys.source$);

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      1.77       5.04      40238      40264          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      1.77       5.04      40238      40264          0           1




SELECT
       sum(cnt)
  FROM (SELECT /*+ full(source$) */
               count(SOURCE) cnt
          FROM sys.source$
        UNION ALL
        SELECT /*+ full(source$) */
               count(SOURCE)
          FROM sys.source$)

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      1.28       2.90      40198      40264          0           1
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      1.28       2.90      40198      40264          0           1

It is a known issue that getting the time information from the O/S is the sensitive part of that operation, and probably the 9.2.0.8 port on AIX is much more efficient in that regard than other ports.

When taking stack traces during such a long running execution, in particular when using high sample frequencies, it can be seen that almost all time is spent on the ftime function calls.

Randolf

I also gave a try to your hinted source$ example (response to sid). There is not such a huge difference between queries. It is 3 vs 3.5 seconds (with 2.9 million rows in sys,source$) on my database (9.2.0.8 AIX 5L 5.3 POWER6 4208MHz, 8 CORES). It seems data pipelining between execution plan operators is much faster on AIX. Will uload tkprof output later (now I’m too tired), too.

Regards
Pavol Babel

Regards

Pavol Babel

I find that a little surprising – it certainly reproduces on 9.2.0.8 on windows, and I wouldn’t have thought that a change of O/S would cause a change in plan.

The idea was a good one, but Oracle does get a bit clever with constants and counts. If you want to use the projection information to demonstrate the size of the data flow you need to select and count a non-null column from the table and use that column name all the way through the query. Here’s a sample that uses source$ to make the point:

PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID  3g2w174t501g6, child number 0
-------------------------------------
select         /*+ gather_plan_statistics */         count(source) from    (
   select /*+ full(source$) */ source from source$         union all
select /*+ full(source$) */ source from source$         )

Plan hash value: 3996963393

------------------------------------------------------------------------------------------
| Id  | Operation            | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
------------------------------------------------------------------------------------------
|   1 |  SORT AGGREGATE      |         |      1 |      1 |      1 |00:00:00.55 |    9782 |
|   2 |   VIEW               |         |      1 |    569K|    571K|00:00:10.86 |    9782 |
|   3 |    UNION-ALL         |         |      1 |        |    571K|00:00:06.86 |    9782 |
|   4 |     TABLE ACCESS FULL| SOURCE$ |      1 |    284K|    285K|00:00:01.43 |    4891 |
|   5 |     TABLE ACCESS FULL| SOURCE$ |      1 |    284K|    285K|00:00:01.14 |    4891 |
------------------------------------------------------------------------------------------

Column Projection Information (identified by operation id):
-----------------------------------------------------------
   1 - (#keys=0) COUNT("SOURCE")[22]
   2 - "SOURCE"[VARCHAR2,4000]
   3 - STRDEF[4000]
   4 - "SOURCE"[VARCHAR2,4000]
   5 - "SOURCE"[VARCHAR2,4000]

select count(*)
from (
	select null from big_table
	union all
	select null from big_table
);

------------------------------------------------------------------------
| Id  | Operation		| Name | Rows  | Cost (%CPU)| Time     |
------------------------------------------------------------------------
|   0 | SELECT STATEMENT	|      |     1 |  8926	 (2)| 00:01:48 |
|   1 |  SORT AGGREGATE 	|      |     1 |	    |	       |
|   2 |   VIEW			|      |  7984K|  8926	 (2)| 00:01:48 |
|   3 |    UNION-ALL		|      |       |	    |	       |
|   4 |     INDEX FAST FULL SCAN| FOO  |  3992K|  4463	 (2)| 00:00:54 |
|   5 |     INDEX FAST FULL SCAN| FOO  |  3992K|  4463	 (2)| 00:00:54 |
------------------------------------------------------------------------

Column Projection Information (identified by operation id):
-----------------------------------------------------------

   1 - (#keys=0) COUNT(*)[22]


select count(*)
from (
	select 1 from big_table
	union all
	select 1 from big_table
);

---------------------------------------------------------------------------------
| Id  | Operation		 | Name | Rows	| Bytes | Cost (%CPU)| Time	|
---------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	 |	|     1 |    13 |  8926   (2)| 00:01:48 |
|   1 |  SORT AGGREGATE 	 |	|     1 |    13 |	     |		|
|   2 |   VIEW			 |	|     2 |    26 |  8926   (2)| 00:01:48 |
|   3 |    UNION-ALL		 |	|	|	|	     |		|
|   4 |     SORT AGGREGATE	 |	|     1 |	|	     |		|
|   5 |      INDEX FAST FULL SCAN| FOO	|  3992K|	|  4463   (2)| 00:00:54 |
|   6 |     SORT AGGREGATE	 |	|     1 |	|	     |		|
|   7 |      INDEX FAST FULL SCAN| FOO	|  3992K|	|  4463   (2)| 00:00:54 |
---------------------------------------------------------------------------------

Column Projection Information (identified by operation id):
-----------------------------------------------------------

   1 - (#keys=0) SUM("CNT")[22]
   2 - "CNT"[NUMBER,22]
   3 - STRDEF[22]
   4 - (#keys=0) COUNT(*)[22]
   6 - (#keys=0) COUNT(*)[22]