Inserts performance issues

I'm trying to evaluate the performance of Oracle with regards to insert rates over a prolonged period.

Two tables are concerned, with 16 columns in total, 9 of which are indexed (these indexes are a must). The problem: the rate at which inserts occur drops off rapidly with increased row numbers and becomes especially noticeable when the total number of rows in a particular table exceeds one million rows. This observation is expected, however, the extent of the performance hit was not anticipated. Is there any way to alleviate this situation. Are there any advanced indexing options I can apply. I've thought of creating a new table periodically , thereby keeping a relatively small index throughout (although I am relunctant to employ this approach because of querying complexities spanning multiple tables).

Any tips/workarounds much appreciated.

--
Posted via dBforums, http://dbforums.com