Thanks for the answer.
Can you plz also let me know the maximum size of this parameter on Windows NT and UNIX platform.

I have one more doubt.
I would be help full if some body can clear this doubt also.

Before asking this question ,I would like to tell you that I am working at one of my companies client site.Here I have found that on certain big tables, indexes are made on 3-4 columns but name of the index is common for all the indexes on each column.It seams to be very strange to me.
My question is that,how oracle optimizer will decide,which index to follow if it tries to perform index scan.
I have checked out optimizer is performing full table scan on all these tables.The optimizer mode is "CHOOSE"
Is this is the reason why optimizer is not able to perform index scan and doing full tble scan?

In this case should I need to rebuild all the indexes on these tables.

Regards,
Saurabh