How to include optimizer hints in Discoverer

Question

We have a Discoverer report which used to run fine prior to DB migration from (9.2.0.6 to 10G Rac 10.2.0.4).
Since the database is migrated to 10g RAC same reports is running for longer time and failes with ROW_ID error,
we ran the sql generated by the report in SQL Plus with below optimizer hint.
Select /*+ optimizer_features_enable('9.2.0') */
this query ran well with optimizer hint, but i am wondering how to use the optimizer hint in Discoverer Plus/Desktop.
Select /*+ optimizer_features_enable('9.2.0') */
C.EMPLOYEE_NUMBER||' '||A.EMPLOYEE_NAME, A.REPORTS_TO, C.SERVICE_CODE, COUNT(B.ACCOUNT_NUMBER)
FROM PSTAGE.NEW_EMPLOYEE_MASTER A,
PSTAGE.NEW_ALL_WORK_ORDER_MASTER B,
PSTAGE.NEW_ALL_WORK_ORDER_DETAIL C
WHERE ( ( B.WORK_ORDER_NUMBER = C.WORK_ORDER_NUMBER AND B.SITE_ID = C.SITE_ID )
AND ( A.EMPLOYEE_NUMBER = C.EMPLOYEE_NUMBER AND A.SITE_ID = C.SITE_ID ) )
AND ( B.WO_STATUS <> 'CN' )
AND ( C.EMPLOYEE_NUMBER = ANY(SELECT S254_200018.EMPLOYEE_NUMBER
FROM PSTAGE.NEW_EMPLOYEE_MASTER S254_199317,
PSTAGE.NEW_ALL_WORK_ORDER_MASTER S254_199854,
PSTAGE.NEW_ALL_WORK_O
Thanks in advance

Answer 1

Hi Sunil
In the Administrator tool, you can add hints to the driving folder used in your query. A first glance at your report seems to indicate that B might be the driver.
If you launch the Administrator tool, open the business area then right-click on the folder in question you can select Properties. The second to last property is called Optimizer hints. Try setting the same hint in here exactly the way you would do it inside SQL.
I am not 100% sure whether this would take as this isn't a folder hint per se, but it is worth a try. You might also want to look at this thread: how to design Optimizer hints  to the generated SQL
Another thing to check is to look at the code that is being generated by your Discoverer worksheets. Do you by chance see a NOREWRITE hint being added? This is a common issue with newer systems. This hint tells the database that the query cannot be rewritten which in most cases will cause poor performance. If this is happening to you I advise you to disable that hint. This is done by editing the pref.txt and adding a new preference called
Out of the box, Discoverer Plus will sometimes add the NOREWRITE hint. This will cause Plus worksheets to operate much slower than Desktop worksheets. You can disable the NOREWRITE hint by adding a new preference called UseNoRewriteHint to pref.txt in the Database section. After you have done this you will have to run the apply preferences script.
[Database]
UseNoRewriteHint = 0
Be sure to close all of your IE windows so that a new JVM is loaded.
For example, you might turn on UseNoRewriteHint (i.e. set it to 1) if you want users to always query against the latest data (e.g. created today), even though this might be slower than querying the summary data (e.g. created yesterday). The NOREWRITE hint instructs the optimizer to disable query rewrite for the query block, which overrides the setting of the parameter QUERY_REWRITE_ENABLED.
Default Value: 0
Valid Values
0 = Do not add the NOREWRITE hint. This is the one I recommend.
1 = Do add the NOREWRITE hint.
Another possible area is with query prediction. This is taken from an Oracle Note: Under some circumstance when you run a query against an Oracle 10g database, the queryprediction might take up the majority of time and CPU may hit 100%.
The cause for this is an an Oracle10g (10.1) database issue but seeing as you are on 10.2 this might not be an issue any more. I throw it out there just in case you still hvae issues and want to raise this with Oracle. The last I heard is that the root cause was still under investigation in an unpublished Bug:4024370. There was a workaround to the issue:
1. Disable Query Prediction (strongly recommended anyway):
For Plus/Viewer:
Edit pref.txt on the middle-tier server and set QPPEnable=0
Run the applypreferences script (.sh or .bat)
For Desktop:
Edit the registry and set QPPEnable=0
HKEY_CURRENT_USERS\Software\ORACLE\Discoverer <version>\Database
2. If you still wish to use Query Prediction while the database issue is being investigate, then you can configure the Query Predictor to use the Explain Plan method rather than the Dynamic Views method.
For Plus/Viewer:
Edit pref.txt on the middle-tier server and set QPPObtainCostMethod=0
Run the applypreferences script (.sh or .bat)
For Desktop:
Edit the registry and set QPPObtainCostMethod=0
HKEY_CURRENT_USERS\Software\ORACLE\Discoverer <version>\Database
Hope this helps
Best wishes
Michael