Value setting for optimizer_index_caching

[omegamark]

select * from ACT where STATUS='I'
Total rows in a table 508633
no of rows returned is 4
Index is there on status column .
optimizer_mode=choose

The index is not used ..Under rule based optimizer it works .
when given a hint the index is used ..

what values should I give under thses circumstance for these two parameters to make index usage ...

optimizer_index_caching 0
optimizer_index_cost_adj 100

[aarroyob]

I have had the best results with:

optimizer_index_caching=80
optimizer_index_cost_adj=10

For more information check this Url:

http://www.EvDBT.com/

Regards

Angel

[julian]

After testing these parameters I noticed that they have almost now influence on the speed of the queries. Probably depends on the system.

[grjohnson]

Julian is correct, changes to these setting may give you no benefit, and even unpredicible timings.

I'd be checking you have analyzed your ACT table. Because if there are no statistics present, Oracle with select to run RULE optimizer as a default when optimizer_mode=choose.

Good luck,

[moff]

Hi,

What type of index is on the status column?

If the cardinality of the column is low try creating this index as a bitmap - It may speed up the query.

Cheers
Moff

[julian]

Bitmap indexes may speed up many ad hoc queries, yes, but you should not forget to set up proper values for CREATE_BITMAP_AREA_SIZE and BITMAP_MERGE_AREA_SIZE.

[pando]

what is your db, oltp or dwh?

is your data distribution uniform?

[omegamark]

the database is oltp type ...
The data is distibuted evenly ..

i have indexed tables ,indexes then also it is not using the indexes .On rule based it uses the indexes ....

[omegamark]

I deleted the statistics now the index is working ...

[pando]

Well I guess your status column has very low cardinality... how many distinct status do you have?

Your data is not distributed evenly, I just saw the number of rows returned, 4 out of half million.... if you generate histograms for that index most probably optimizer would use the index for that specific query. However if your application is using bind variables then histograms is useless....

Also by deleteing statistics is forcing using RULE optimizer

Try generate the histogram wth 20 hash buckets see if it uses optimizer, if not increase hash buckets to 40 and see

But are you sure your query is faster with RULE optimizer????