reorder table data

Hi,

I have a 40GB database with a few tables containing approx 10 million rows.  
Most of the data in these tables is inactive and there is only a few rows 
which get used for our benchmark run each day. We cannot delete the inactive 
data since it might be required for a particular run some day while it is 
active data that is used mostly. Problem here is that the update and select 
queries are very slow becuase of this background data. I am looking for some 
way to reorganize the data in such a way that the active data gets accessed 
much faster as compared to inactive data. I am using btree indices which 
assumes that all the rows have the same probability. Is there an index or 
some other way to order this data so that active data can be accessed most 
efficiently (want to reduce the effect of background data as much as 
possible).??

Also, what is the best way to find out which rows are getting accessed in a 
table for a particular run??

Regards,
Vinita Bansal

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