slow inserts

[mjschwenger]

I have a heavy insert database - 3rd party application which checks for existance of a record, and if they are not there, it inserts them in 10 major tables. I'm running 36 instances of this application and have about 25,000 inserts per table/per minute. Unfortunately, this throuput is not enough for the business and I'm trying to optimize it. What wonders me is that if I add more application instances the insert rate doesn't improve. Bellow is a part of my statpack.
Please help me analyze what is the problem and what can I do to improve the performance.
Thanks a lot,mj

Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event                          Waits Time (s) Call Time
------------------------- ---------- -------- ---------
db file sequential read   10,147,781   96,505     88.00
CPU time                       7,286     6.64
db file parallel write       102,185    2,391      2.18
log file sync                165,362    1,649      1.50
log file parallel write      297,068    1,251      1.14