Hi Tamilselvan

1. I am using a Index Cluster
2. Yes, might be you are right. The problem might be with the size. I am pasting the storage here. Pls advise me. The current size of the table is around half tera bytes. And perday inserts is around 4-5 GB.
(Pct_free: 1
pct_used: 98
initial extent: 1M
Next Extent: 1M
Min Extents: 1
Max extents 2147483645
Pct_increase 0
freelists 97
)

3. Only one table in the cluster.

Most Imp
4. I can not reclaim the deleted space!! (I tried Alter cluster deallocate unused!! it is also not working!!)

It is a production problem and hence anxiously looking forward to your reply.