Performance of insert on duplicate key update

[Ravi Malghan]

Hi:I am on mysql 5.5. I have a large InnoDB table (~30M rows). I have about 4-5K insert on duplicate key update queries every 5 minutes. As table grows these inserts are becoming slower and slower. I added partitioning to the table by a timestamp field. This version doesn't support explain plan for inserts and updates. Is there a way to limit the number of partitions the query scans for updates? In other words is there a way to include the timestamp field in my insert on duplicate key update query?

Thanks
Ravi