costs of inserts and influence of caching tables and foreign keys etc

Hi,

I have quit some inserts that are reported through explain plan as relatively expensive (like 2000 by cost-based) I did experiment a little by caching some small reference tables and removing some seemed to be unnecessay indexes.

One example is a table with 590.000 rows, 5 constraints (primary and foreign keys), 5 indexes and an insert on that table is reported to cost 2441.

1. is this really expensive
2. how can I measure or experiment with caching tables compared to not populating the complete buffer cache with those cached tables
3. is it wise to consider removing maybe some indexes and/or constraints ?

Thanks,

Jeroen

Data: HP UX 10.01

         Oracle 7.3.2.3
         MTS