Oracle Database 10g runs I/O operations from both shared memory and process-private regions using the new HP-UX asynchronous driver. However, I/O operations through the asynchronous driver are not asynchronous in nature. This is because Oracle Database must perform a blocking wait to check the status of I/O operations submitted to the asynchronous driver. This causes some Oracle processes, such as the database writer process, to essentially process synchronous I/O.
This is an extract from
this link
seems like asynchronous I/O on HP-UX with Oracle is only supported for raw FS
How many DB writer are currently set up on your DB ?
Few considerations about it you might want to prefer:
a) the FS type hosting the datafile can handle async I/O (oracle param DISK_ASYNCH_IO = true) so the DB writer can let the OS deal with the update (without having to do "wait" events)
b) if your FS type doesn't support async I/O you can setup more than 1 DBWR (DBWR_PROCESSES/db_writer_processes) but since the oracle buffer cache is divided in as much working sets, you might want to adjust the DB_BLOCK_LRU_LATCHES.
c) Last solution, activate the forking to simulate asynch I/O by activating the use of slave processes (DBWn_IO_SLAVES) which are in fact synchronous I/O (DISK_ASYNCH_IO = false). Risks of that last solution are buffer overhead, wait, memory overhead (IPCs & context switch)