Explain plan, Oracle 10g, AWR, ASH etc etc

Hi,
I'm obviously not searching on the right terms but using one of the following : AWR, ASH, ADDM, isn't it possible to get the explain plan for a certain SQL_ID after the fact?
I was sure that using ash and specifying the SQL_ID that one could have the explain plan, but I don't have it in the ASH Report. We don't have Grid in place, only snapshots taken every hour.
cheers.

Thankyou both for your very quick replies, just what I needed.
Edited by: mattyb on Mar 25, 2009 2:06 PM

Similar Messages

Interpreting explain plans oracle 11gr2

Hi,
We are using oracle 11.2.0.3 and plan on evaluating a series of explain plans to determine index/partitioning strategy for a large fact table +a ssociarted dimensions in data warehouse.
Whilst we plan on running a selection of these to get actaul times, wish to evalaute many more eplain plans to guage efficiency of data model.
In terms of interpreting we are going on basis of the lower the row count/cpu cost the better the performance should be.
Plan on using autotrace for these as well.
Any downsides to this /shoudl we look out for anything esle with explain plan.
Is autotrace suffciient in this repsect.
Have also found the time in execution plan can often bear no resembalnce to actaul execution plan.
Any other tips on interpreting explain plans woudl eb appreacited.
Whilst I understand the real times will only come thorugh running the queries want to do prep work with explain plans before run them all.
Thanks
Edited by: user5716448 on 02-Mar-2013 08:26

Don't rely on the cost to tell you how efficient a SQL is. It is based on estimates that are not always correct. Its best use is to tell if something has changed when doing SQL variations - it can and does happen that a lower cost version will use more resources as per AUTOTRACE than a higher-cost version of the SQL.
Also make absoutely sure that the tuned SQL returns the same results as the original :)
Using AUTOTRACE was a good decision. It will provide run-time metrics for your SQL as well as automatically generate execution plans. It does not list CPU usage, which is avialable from V$SQL. Lower resources listed by AUTOTRACE should accompany faster run times in general.

Interpreting Explain Plan - Oracle

Hi Guys,
Can advise on this.. try searching around the web but can't find explanation.
What does the Cost and %CPU stands for?
thanks

>
The cost is an estimated value proportional to the expected resource use needed to execute the statement with a particular plan. The optimizer calculates the cost of access paths and join orders based on the estimated computer resources, which includes I/O, CPU, and memory.
>
Please read http://download.oracle.com/docs/cd/E11882_01/server.112/e16638/optimops.htm#i82005.

Very different execution plan in Oracle 10g vs. 9i

Good afternoon,
A few days ago I migrated an Oracle database 9i to 10g.
Right now I have an exact copy of the 9i instance running on another machine.
I noticed that the time for some queries take much more. For example, when comparing the execution plan for this query on the instance with Oracle 9i and Oracle 10g instance, I see that the cost in 10g is 94981765382, while in 9i is 120106.
Any idea what might be happening?
Execution Plan Oracle 9: http://blog.davidlozanolucas.com/uploads/execution_plan_Oracle_9i.jpg
Execution Plan Oracle 10g: http://blog.davidlozanolucas.com/uploads/execution_plan_Oracle_10g.jpg
Edited by: david_lozano_lucas on Dec 14, 2011 4:54 PM

Sorry,
Here are the details.
For Oracle 9i:
PLAN_TABLE_OUTPUT
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Pstart| Pstop | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 16M| 3675M| | 120K (0)| | | | | |
|* 1 | FILTER | | | | | | | | | | |
|* 2 | HASH JOIN | | 16M| 3675M| | 120K (0)| | | 03,09 | P->S | QC (RAND) |
| 3 | TABLE ACCESS FULL | ORG_LOC_DM | 2261 | 13566 | | 8 (0)| | | 03,01 | S->P | HASH |
|* 4 | HASH JOIN OUTER | | 16M| 3582M| 1023M| 120K (0)| | | 03,08 | P->P | HASH |
|* 5 | HASH JOIN OUTER | | 16M| 2783M| 1041M| 102K (0)| | | 03,08 | PCWP | |
|* 6 | HASH JOIN OUTER | | 16M| 2521M| 715M| 69515 (0)| | | 03,08 | PCWP | |
| 7 | PARTITION RANGE ALL | | | | | | 1 | 14 | 03,08 | PCWP | |
| 8 | TABLE ACCESS FULL | SURT_SKU_LD_DM | 16M| 1922M| | 60988 (0)| 1 | 14 | 03,04 | P->P | HASH |
| 9 | VIEW | | 909K| 33M| | | | | 03,05 | P->P | HASH |
| 10 | SORT GROUP BY | | 909K| 19M| 62M| 1553 (0)| | | 03,05 | PCWP | |
|* 11 | HASH JOIN | | 909K| 19M| | 164 (0)| | | 03,05 | PCWP | |
|* 12 | TABLE ACCESS FULL| ORG_LOC_DM | 1131 | 6786 | | 8 (0)| | | 03,00 | S->P | HASH |
|* 13 | TABLE ACCESS FULL| INV_MOVE_SKU_LCM_DM | 909K| 13M| | 154 (0)| 60 | 60 | 03,02 | P->P | HASH |
|* 14 | TABLE ACCESS FULL | SURT_SKU_LCM_DM | 16M| 260M| | 6457 (0)| 59 | 59 | 03,06 | P->P | HASH |
| 15 | VIEW | | 1795K| 89M| | | | | 03,07 | P->P | HASH |
| 16 | SORT GROUP BY | | 1795K| 63M| 233M| 4565 (0)| | | 03,07 | PCWP | |
|* 17 | TABLE ACCESS FULL | SLS_SKU_LCM_DM | 1795K| 63M| | 599 (0)| 60 | 60 | 03,03 | P->P | HASH |
| 18 | NESTED LOOPS | | 1 | 16 | | 7 (15)| | | | | |
| 19 | TABLE ACCESS FULL | MAINT_LOAD_DT | 1 | 8 | | 1 (0)| | | | | |
|* 20 | INDEX RANGE SCAN | DAY_IDNT_I1 | 1 | 8 | | 1 (0)| | | | | |
Predicate Information (identified by operation id):
1 - filter("SYS_ALIAS_1"."DAY_IDNT"= (SELECT /*+ */ :B1 FROM "RDW91_DM"."MAINT_LOAD_DT" "Y","RDW91_DM"."TIME_DAY_DM" "X" WHERE
"X"."DAY_DT"="Y"."CURR_LOAD_DT"))
2 - access("SYS_ALIAS_1"."LOC_KEY"="G"."LOC_KEY")
4 - access("SYS_ALIAS_1"."LOC_KEY"="I"."LOC_KEY"(+) AND "SYS_ALIAS_1"."SKU_KEY"="I"."SKU_KEY"(+))
5 - access("SYS_ALIAS_1"."LOC_KEY"="B"."LOC_KEY"(+) AND "SYS_ALIAS_1"."SKU_KEY"="B"."SKU_KEY"(+))
6 - access("SYS_ALIAS_1"."LOC_KEY"="J"."LOC_KEY"(+) AND "SYS_ALIAS_1"."SKU_KEY"="J"."SKU_KEY"(+))
11 - access("A"."LOC_KEY"="B"."LOC_KEY")
12 - filter("B"."LOC_TYPE_CDE"='W')
13 - filter("A"."CMTH_IDNT"=201112)
14 - filter("B"."CMTH_IDNT"(+)=201111)
17 - filter("SLS_SKU_LCM_DM"."CMTH_IDNT"=201112)
20 - access("X"."DAY_DT"="Y"."CURR_LOAD_DT")
For 10g:
PLAN_TABLE_OUTPUT
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost | Pstart| Pstop | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 16M| 3685M| | 94G| | | | | |
| 1 | FILTER | | | | | | | | | | |
| 2 | PX COORDINATOR | | | | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10008 | 16M| 3685M| | 94G| | | Q1,08 | P->S | QC (RAND) |
| 4 | BUFFER SORT | | 16M| 3685M| | | | | Q1,08 | PCWP | |
| 5 | NESTED LOOPS OUTER | | 16M| 3685M| | 94G| | | Q1,08 | PCWP | |
| 6 | HASH JOIN | | 16M| 3424M| | 201K| | | Q1,08 | PCWP | |
| 7 | BUFFER SORT | | | | | | | | Q1,08 | PCWC | |
| 8 | PX RECEIVE | | 2261 | 13566 | | 8 | | | Q1,08 | PCWP | |
| 9 | PX SEND HASH | :TQ10001 | 2261 | 13566 | | 8 | | | | S->P | HASH |
| 10 | TABLE ACCESS FULL | ORG_LOC_DM | 2261 | 13566 | | 8 | | | | | |
| 11 | PX RECEIVE | | 16M| 3332M| | 201K| | | Q1,08 | PCWP | |
| 12 | PX SEND HASH | :TQ10007 | 16M| 3332M| | 201K| | | Q1,07 | P->P | HASH |
| 13 | HASH JOIN OUTER BUFFERED | | 16M| 3332M| 982M| 201K| | | Q1,07 | PCWP | |
| 14 | HASH JOIN OUTER | | 16M| 2733M| 735M| 127K| | | Q1,07 | PCWP | |
| 15 | PX RECEIVE | | 16M| 1934M| | 75785 | | | Q1,07 | PCWP | |
| 16 | PX SEND HASH | :TQ10004 | 16M| 1934M| | 75785 | | | Q1,04 | P->P | HASH |
| 17 | PX BLOCK ITERATOR | | 16M| 1934M| | 75785 | 1 | 14 | Q1,04 | PCWC | |
| 18 | TABLE ACCESS FULL | SURT_SKU_LD_DM | 16M| 1934M| | 75785 | 1 | 14 | Q1,04 | PCWP | |
| 19 | PX RECEIVE | | 1450K| 71M| | 3892 | | | Q1,07 | PCWP | |
| 20 | PX SEND HASH | :TQ10005 | 1450K| 71M| | 3892 | | | Q1,05 | P->P | HASH |
| 21 | VIEW | | 1450K| 71M| | 3892 | | | Q1,05 | PCWP | |
| 22 | SORT GROUP BY | | 1450K| 53M| 188M| 3892 | | | Q1,05 | PCWP | |
| 23 | PX RECEIVE | | 1450K| 53M| | 562 | | | Q1,05 | PCWP | |
| 24 | PX SEND HASH | :TQ10002 | 1450K| 53M| | 562 | | | Q1,02 | P->P | HASH |
| 25 | PX BLOCK ITERATOR | | 1450K| 53M| | 562 | 60 | 60 | Q1,02 | PCWC | |
| 26 | MAT_VIEW ACCESS FULL| SLS_SKU_LCM_DM | 1450K| 53M| | 562 | 60 | 60 | Q1,02 | PCWP | |
| 27 | PX RECEIVE | | 652K| 24M| | 1150 | | | Q1,07 | PCWP | |
| 28 | PX SEND HASH | :TQ10006 | 652K| 24M| | 1150 | | | Q1,06 | P->P | HASH |
| 29 | VIEW | | 652K| 24M| | 1150 | | | Q1,06 | PCWP | |
| 30 | SORT GROUP BY | | 652K| 14M| | 1150 | | | Q1,06 | PCWP | |
| 31 | HASH JOIN | | 652K| 14M| | 128 | | | Q1,06 | PCWP | |
| 32 | BUFFER SORT | | | | | | | | Q1,06 | PCWC | |
| 33 | PX RECEIVE | | 1131 | 6786 | | 8 | | | Q1,06 | PCWP | |
| 34 | PX SEND HASH | :TQ10000 | 1131 | 6786 | | 8 | | | | S->P | HASH |
| 35 | TABLE ACCESS FULL | ORG_LOC_DM | 1131 | 6786 | | 8 | | | | | |
| 36 | PX RECEIVE | | 652K| 10M| | 118 | | | Q1,06 | PCWP | |
| 37 | PX SEND HASH | :TQ10003 | 652K| 10M| | 118 | | | Q1,03 | P->P | HASH |
| 38 | PX BLOCK ITERATOR | | 652K| 10M| | 118 | 60 | 60 | Q1,03 | PCWC | |
| 39 | MAT_VIEW ACCESS FULL| INV_MOVE_SKU_LCM_DM | 652K| 10M| | 118 | 60 | 60 | Q1,03 | PCWP | |
| 40 | PARTITION RANGE SINGLE | | 1 | 17 | | 8609 | 59 | 59 | Q1,08 | PCWP | |
| 41 | TABLE ACCESS FULL | SURT_SKU_LCM_DM | 1 | 17 | | 8609 | 59 | 59 | Q1,08 | PCWP | |
| 42 | NESTED LOOPS | | 1 | 16 | | 6 | | | | | |
| 43 | TABLE ACCESS FULL | MAINT_LOAD_DT | 1 | 8 | | 1 | | | | | |
| 44 | INDEX RANGE SCAN | DAY_IDNT_I1 | 1 | 8 | | 5 | | | | | |
Note
- 'PLAN_TABLE' is old version
- cpu costing is off (consider enabling it)

How to install oracle 10g in Solaris10 Container

I'd like to install oracle 10g in local zone of Solaris 10.
But I don't know how to set "set noexec_user_stack=1".
Now before install oracle 10g.
I created /etc/system file in local zone.
The file content is only "set noexec_user_stack=1".
And I performed "set noexec_user_stack=1" command as root.
Do I need to include "set noexec_user_stack=1" in /etc/system file in global zone?
Please advice.

did you check this?
Installing OCS 10g R1 on Solaris 10

Compatability Matrix for Oracle 10g

I'm searching for the compatability matrix for Oracle 10g database. Need certified combinations for Operating system (Unix/Windows), Application servers (BEA/IBM) , Web servers, etc.
Can anyone post me the link?
Thanks in advance.

I'm searching for the compatability matrix for Oracle 10g database. Need certified combinations for Operating system (Unix/Windows)Here: http://www.oracle.com/technology/support/metalink/index.html
Application servers (BEA/IBM) , Web servers, etc.There are not cert. matrices for app. servers from other vendors.
You can use whathever application server in combination with Oracle 10g BEA/IBM/JBOSS, etc. Everything you need appropriate client (for example for application in Java - Oracle JDBC connector which is free to download).

[8i] Can someone help me on using explain plan, tkprof, etc.?

I am trying to follow the instructions at When your query takes too long ...
I am trying to figure out why a simple query takes so long.
The query is:
SELECT COUNT(*) AS tot_rows FROM my_table;It takes a good 5 minutes or so to run (best case), and the result is around 22 million (total rows).
My generic username does not (evidently) allow access to PLAN_TABLE, so I had to log on as SYSTEM to run explain plan. In SQL*Plus, I typed in:
explain plan for (SELECT COUNT(*) AS tot_rows FROM my_table);and the response was "Explained."
Isn't this supposed to give me some sort of output, or am I missing something?
Then, the next step in the post I linked is to use tkprof. I see that it says it will output a file to a path specified in a parameter. The only problem is, I don't have access to the db's server. I am working remotely, and do not have any way to remotely (or directly) access the db server. Is there any way to have the file output to my local machine, or am I just S.O.L.?

SomeoneElse used "create table as" (CTAS), wich automatically gathers the stats. You can see the differende before and after stats clearly in this example.
This is the script:
drop table ttemp;
create table ttemp (object_id number not null, owner varchar2(30), object_name varchar2(200));
alter table ttemp add constraint ttemp_pk primary key (object_id);
insert into ttemp
select object_id, owner, object_name
from dba_objects
where object_id is not null;
set autotrace on
select count(*) from ttemp;
exec dbms_stats.gather_table_stats('PROD','TTEMP');
select count(*) from ttemp;And the result:
Table dropped.
Table created.
Table altered.
46888 rows created.
COUNT(*)
     46888
1 row selected.
Execution Plan
           SELECT STATEMENT Optimizer Mode=CHOOSE
   1         SORT AGGREGATE
   2    1      TABLE ACCESS FULL PROD.TTEMP
Statistics
          1 recursive calls
          1 db block gets
        252 consistent gets
          0 physical reads
        120 redo size
          0 PX remote messages sent
          0 PX remote messages recv'd
          0 buffer is pinned count
          0 workarea memory allocated
          4 workarea executions - optimal
          1 rows processed
PL/SQL procedure successfully completed.
COUNT(*)
     46888
1 row selected.
Execution Plan
           SELECT STATEMENT Optimizer Mode=CHOOSE (Cost=4 Card=1)
   1         SORT AGGREGATE (Card=1)
   2    1      INDEX FAST FULL SCAN PROD.TTEMP_PK (Cost=4 Card=46 K)
Statistics
          1 recursive calls
          2 db block gets
        328 consistent gets
          0 physical reads
       8856 redo size
          0 PX remote messages sent
          0 PX remote messages recv'd
          0 buffer is pinned count
          0 workarea memory allocated
          4 workarea executions - optimal
          1 rows processed

Availability of the SQL/XML functions (XMLELEMENT, etc.) in Oracle 10g XE

Hi,
I have installed Oracle 10g XE on a Windows PC. According to the Oracle XML DB Developer's Guide p.2-1, the installation of the Oracle XML DB can be checked via the following commands:
select * from all_users;
describe resource_view
I ran both commands and got the desired output according to the Developer's guide, i.e.: The user XDB exists and so does the view resource_view. However, when I ran a small test with the XMLELEMENT function, then I got unsatisfactory results:
Example:
SELECT
XMLELEMENT (
NAME Land,
XMLATTRIBUTES (L.LCode AS LCode),
XMLELEMENT (NAME LName, L.LName)
) AS Mondial
FROM Land L;
Output on Oracle 10g XE:
MONDIAL
SYS.XMLTYPE
SYS.XMLTYPE
SYS.XMLTYPE
SYS.XMLTYPE
Expected output (which I got from a successful run on an Oracle 10g EE Server):
MONDIAL
<LAND LCODE="A "><LNAME>Austria</LNAME></LAND>
<LAND LCODE="F "><LNAME>France</LNAME></LAND>
<LAND LCODE="D "><LNAME>Germany</LNAME></LAND>
<LAND LCODE="I "><LNAME>Italy</LNAME></LAND>
i.e., rather than the four XML elements, I just got four times the output sys.xmltype - which is of course useless. What can I do to get the desired output? Thank you for your help.
Reini, user524179

What program are you using to run the sql? Are you sure you are using sql*plus for getting this?
Output on Oracle 10g XE:
MONDIAL
SYS.XMLTYPE
SYS.XMLTYPE
SYS.XMLTYPE
SYS.XMLTYPE

Oracle 10g Diff in execution plan query with binding var Vs without

We recently did 10g upgrade. In 10g, execution plan differs for query with binding var(thru jdbc etc) Vs without it as given below. For query with binding var,
it chooses poor execution plan(no index is used, full scan is done etc). everything worked fine in 9i. To rectify the problem, we have to hint query with right index,join etc. but i dont like this solution.
I would rather prefer to correct database to choose right execution path instead of eacy query level. but not sure what causes the issue.
Does anybody came across this issue? if so, Please share your experiences. Thanks for the help. Do let me know if you need more info.
1. Query without binding bar:
select * from test where col1 = :1 and col2 = :2
1. Query without binding bar:
select * from test where col1 = 'foo' and col2= 'bar'

I am not an expert but in my humble opinion it is the developer's responsability to ensure the correct explain plan is used before deploying code to production, if the explain plan returned by the DB is bad, then the use of a hint is perfectly acceptable.
Check this out: http://lcgapp.cern.ch/project/CondDB/snapshot/performance.html
Excerpt:
Bind variable peeking. If an SQL query contains bind variables, the optimal execution plan may depend on the values of those variables. When the Oracle query optimizer chooses the execution plan for such a query, it may indeed look at the values of all bind variables involved: this is known as "bind variable peeking".
In summary, the execution plan used for a given SQL query cannot be predicted a priori because it depends on the presence and quality of statistics and on the values of bind variables used at the time the query was first executed (hard-parsed). As a consequence of this instability of execution plans, very different performances may be observed for the same SQL query. In COOL, this issue is addressed by adding Oracle hints to the queries, to make sure that the same (good) plan is used in all cases, even with unreliable statistics or unfavourable bind variables.
Edited by: Rodolfo Ferrari on Jun 3, 2009 9:40 PM

Query tunning in Oracle using Explain Plan

Adding to my below question: I have now modified the query and the path shownby 'Explain plan' has reduced. The 'Time' column of plan_table is also showing much lesser value. However, some people are suggesting me to consider the time required by the query to execute on Toad. Will it be practical? Please help!!
Hi, I am using Oracle 11g. I need to optimize a Select query(Need to minimize the execution time). I need to know how 'Explain Plan' would help me. I know how to use Explain Plan command. I refer Plan_table table to see the details of the plan. Please guide me regarding which columns of the Plan_table should be considered while modifying the query for optimization. Some people say, 'Time' column should be considered, some say 'Bytes' etc. Some suggest on minimizing the full table scans, while some people say that I should minimize the total no. operations (less no. of rows should be displayed in Plan_table). As per an experienced friend of mine, full table scans should be reduced (for e.g. if there are 5 full table scans in the plan, then try to reduce them to less than 5. ). However, if I consider any full table scan operation in the plan_table, its shows value of 'time' column as only 1 which is very very less. Does this mean the full scan is actually taking very less time?? If yes, then this means full table scans are very fast in my case and no need to work on them. Some articles suggest that plan shown by 'Explain Plan' command is not necessarily followed while executing the query. So what should I look for then? How should I optimize the query and how will I come to know that it's optimized?? Please help!!...
Edited by: 885901 on Sep 20, 2011 2:10 AM

885901 wrote:
Hi, I am using Oracle 11g. I need to optimize a Select query(Need to minimize the execution time). I need to know how 'Explain Plan' would help me. I know how to use Explain Plan command. I refer Plan_table table to see the details of the plan. Please guide me regarding which columns of the Plan_table should be considered while modifying the query for optimization. Some people say, 'Time' column should be considered, some say 'Bytes' etc. Some suggest on minimizing the full table scans, while some people say that I should minimize the total no. operations (less no. of rows should be displayed in Plan_table). As per an experienced friend of mine, full table scans should be reduced (for e.g. if there are 5 full table scans in the plan, then try to reduce them to less than 5. ). However, if I consider any full table scan operation in the plan_table, its shows value of 'time' column as only 1 which is very very less. Does this mean the full scan is actually taking very less time?? If yes, then this means full table scans are very fast in my case and no need to work on them. Some articles suggest that plan shown by 'Explain Plan' command is not necessarily followed while executing the query. So what should I look for then? How should I optimize the query and how will I come to know that it's optimized?? Please help!!...how fast is fast enough?

Starting Oracle XE on linux by /etc/init.d/oracle-xe start

Hello,
I installed Oracle Database 10g Express Edition on a Linux Ubuntu 7.04 (feisty)
following official installation instructions found here
http://www.oracle.com/technology/software/products/database/xe/files/install.102/b25144/toc.htm#BABCEAHD
but I noticed a weird behavior.
The installation process was ok.
The configuration process (/etc/init.d/oracle-xe configure) was also ok.
I set everything on default except for the “starting on boot” option I choose NO, because the instructions let me understand that I can start the service manually by the command:
$ /etc/init.d/oracle-xe start
The configuration process at the end also started the service well, so I could test my new oracle installation on my web browser following the url http://127.0.0.1:8080/apex
Everything went fine... but...
On the next boot I wanted to start my oracle so I typed
sudo /etc/init.d/oracle-xe start
but nothing happened and the server didn't go up.
Looking into to script /etc/init.d/oracle-xe
we can find this switch
case "$1" in
start)
     if test -f "$CONFIGURATION"
     then
          if test "$ORACLE_DBENABLED" != "true"
          then
               exit 0
          fi
     else
     echo "Oracle Database 10g Express Edition is not configured. You must run
'/etc/init.d/oracle-xe configure' as the root user to configure the database."
          exit 0
     fi
     start
this means that if you chose NO (N) for the “starting on boot” option on the configuration process (NB this choice put false in the env variable ORACLE_DBENABLED) you can't start the dbms by this script.
I try comment the few lines
     then
          #if test "$ORACLE_DBENABLED" != "true"
          #then
          #     exit 0
          #fi
     else
and this time the server starts well.
So I deduced that something was wrong with the script and the official installation instructions.

Yes... Thank you.
But I saw the problem could to be simple avoided using the options
enable/disable for the script /etc/init.d/oracle-xe,
If you choose not to start oracle at boot time, you can start it
manually by the sequence
/etc/init.d/oracle-xe enable
/etc/init.d/oracle-xe start
then when you want to stop it
/etc/init.d/oracle-xe stop
/etc/init.d/oracle-xe disable
by this last command we don't make oracle restart
at the next system boot.
I think it would be a good thing to update the reference
documentation at
http://www.oracle.com/technology/software/products/database/xe/files/install.102/b25144/toc.htm#BABCEAHD
to explain this situation better.

Oracle rownum wrong explain plan

SCOTT@oracle10g>create table t as select * from dba_objects;
Table created.
SCOTT@oracle10g>alter table t modify CREATED date not null;
Table altered.
SCOTT@oracle10g>insert into t select * from t;
50416 rows created.
SCOTT@oracle10g>insert into t select * from t;
100832 rows created.
SCOTT@oracle10g>insert into t select * from t;
201664 rows created.
SCOTT@oracle10g>commit;
Commit complete.
SCOTT@oracle10g>create index t_created on t(created) nologging;
Index created.
SCOTT@oracle10g>select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod
PL/SQL Release 10.2.0.3.0 - Production
CORE    10.2.0.3.0      Production
TNS for 32-bit Windows: Version 10.2.0.3.0 - Production
NLSRTL Version 10.2.0.3.0 - Production
SCOTT@oracle10g>set autot trace
SCOTT@oracle10g>select t.owner,t.object_name   from
2 (select rid from (
3 select rownum rn,rid from
4 (select rowid rid from t order by created)
5 where rownum<100035)
6 where rn>100000) h, t
7 where t.rowid=h.rid;
34 rows selected.
Execution Plan
Plan hash value: 3449471415
| Id | Operation           | Name      | Rows | Bytes |TempSpc| Cost (%CPU)| T
ime     |
|   0 | SELECT STATEMENT    |           |   100K|    11M|       | 4776   (2)| 0
0:00:58 |
|* 1 | HASH JOIN          |           |   100K|    11M| 3616K| 4776   (2)| 0
0:00:58 |
|* 2 |   VIEW              |           |   100K| 2442K|       | 1116   (2)| 0
0:00:14 |
|* 3 |    COUNT STOPKEY    |           |       |       |       |            |
        |
|   4 |     VIEW            |           |   440K| 5157K|       | 1116   (2)| 0
0:00:14 |
|   5 |      INDEX FULL SCAN| T_CREATED |   440K| 9024K|       | 1116   (2)| 0
0:00:14 |
|   6 |   TABLE ACCESS FULL | T         |   440K|    39M|       | 1237   (2)| 0
0:00:15 |
Predicate Information (identified by operation id):
   1 - access("T".ROWID="RID")
   2 - filter("RN">100000)
   3 - filter(ROWNUM<100035)
Note
   - dynamic sampling used for this statement
Statistics
          0 recursive calls
          0 db block gets
       5814 consistent gets
          0 physical reads
          0 redo size
       1588 bytes sent via SQL*Net to client
        422 bytes received via SQL*Net from client
          4 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
         34 rows processed
here ,oracle don't choose the best explain plan ,I think becase oracle compute cadinality 100k ,so it don't choose nest loop,why oracle can't compute cardinality 35 here ??
|* 2 |   VIEW              |           |   100K| 2442K|       | 1116   (2)| 0
SCOTT@oracle10g>select t.owner,t.object_name   from t where rowid in
2      (select rid from (
3      select rownum rn,rid from
4      (select rowid rid from t order by created)
5      where rownum<100035)
6      where rn>100000)
7
SCOTT@oracle10g>/
34 rows selected.
Execution Plan
Plan hash value: 1566335206
| Id | Operation                   | Name      | Rows | Bytes | Cost (%CPU)| T
ime     |
|   0 | SELECT STATEMENT            |           |     1 |   107 | 1586   (2)| 0
0:00:20 |
|   1 | NESTED LOOPS               |           |     1 |   107 | 1586   (2)| 0
0:00:20 |
|   2 |   VIEW                      | VW_NSO_1 |   100K| 1172K| 1116   (2)| 0
0:00:14 |
|   3 |    HASH UNIQUE              |           |     1 | 2442K|            |
        |
|* 4 |     VIEW                    |           |   100K| 2442K| 1116   (2)| 0
0:00:14 |
|* 5 |      COUNT STOPKEY          |           |       |       |            |
        |
|   6 |       VIEW                  |           |   440K| 5157K| 1116   (2)| 0
0:00:14 |
|   7 |        INDEX FULL SCAN      | T_CREATED |   440K| 9024K| 1116   (2)| 0
0:00:14 |
|   8 |   TABLE ACCESS BY USER ROWID| T         |     1 |    95 |     1   (0)| 0
0:00:01 |
Predicate Information (identified by operation id):
   4 - filter("RN">100000)
   5 - filter(ROWNUM<100035)
Note
   - dynamic sampling used for this statement
Statistics
          0 recursive calls
          0 db block gets
        301 consistent gets
          0 physical reads
          0 redo size
       1896 bytes sent via SQL*Net to client
        422 bytes received via SQL*Net from client
          4 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
         34 rows processed
SCOTT@oracle10g>select /*+ordered use_nl(t)*/ t.owner,t.object_name   from
2 (select rid from (
3 select rownum rn,rid from
4 (select rowid rid from t order by created)
5 where rownum<100035)
6 where rn>100000) h, t
7 where t.rowid=h.rid;
34 rows selected.
Execution Plan
Plan hash value: 3976541160
| Id | Operation                   | Name      | Rows | Bytes | Cost (%CPU)| T
ime     |
|   0 | SELECT STATEMENT            |           |   100K|    11M|   101K (1)| 0
0:20:16 |
|   1 | NESTED LOOPS               |           |   100K|    11M|   101K (1)| 0
0:20:16 |
|* 2 |   VIEW                      |           |   100K| 2442K| 1116   (2)| 0
0:00:14 |
|* 3 |    COUNT STOPKEY            |           |       |       |            |
        |
|   4 |     VIEW                    |           |   440K| 5157K| 1116   (2)| 0
0:00:14 |
|   5 |      INDEX FULL SCAN        | T_CREATED |   440K| 9024K| 1116   (2)| 0
0:00:14 |
|   6 |   TABLE ACCESS BY USER ROWID| T         |     1 |    95 |     1   (0)| 0
0:00:01 |
Predicate Information (identified by operation id):
   2 - filter("RN">100000)
   3 - filter(ROWNUM<100035)
Note
   - dynamic sampling used for this statement
Statistics
          0 recursive calls
          0 db block gets
        304 consistent gets
          0 physical reads
          0 redo size
       1588 bytes sent via SQL*Net to client
        422 bytes received via SQL*Net from client
          4 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
         34 rows processed

jinyu wrote:
Thanks for your great reply and posting ,could you tell me why subquery has the least cost here ??
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 107 | 1586 (2)| 00:00:20 |
| 1 | NESTED LOOPS | | 1 | 107 | 1586 (2)| 00:00:20 |
| 2 | VIEW | VW_NSO_1 | 100K| 1172K| 1116 (2)| 00:00:14 |
| 3 | HASH UNIQUE | | 1 | 2442K| | |
|* 4 | VIEW | | 100K| 2442K| 1116 (2)| 00:00:14 |
|* 5 | COUNT STOPKEY | | | | | |
| 6 | VIEW | | 440K| 5157K| 1116 (2)| 00:00:14 |
| 7 | INDEX FULL SCAN | T_CREATED | 440K| 9024K| 1116 (2)| 00:00:14 |
| 8 | TABLE ACCESS BY USER ROWID| T | 1 | 95 | 1 (0)| 00:00:01 |
----------------------------------------------------------------------------------------->
You'll notice that as a result of a "driving" IN subquery Oracle has done a hash unique operation (line 3) on the rowids produced by the subquery. At this point the optimizer has lost all knowledge of the number of distinct values for that data column in the subquery and come back with the cardinality of one. The re-appearance of 100K as the cardinality in line 2 is an error, but I don't think the optimizer has used that value in later arithmetic.
Given the cardinality of one, the obvious path into the T table is a nested loop.
The same type of probelm appears when you use the table() operator in joins - you can use the cardinality() hint to try an tell Oracle how many rows the table() will produce, but that doesn't tell it how many distinct values there are in join columns - and that's an important detail when you work out the join cardinality and method).
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.
"Science is more than a body of knowledge; it is a way of thinking"
Carl Sagan

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