ASA Database Administration Guide
The Database Server
The database server
Database server options
Open files using the operating system disk cache.
{ dbsrv9 | dbeng9 } -u ...
Windows NT/2000/XP, Windows 95/98/Me, UNIX
Files are opened using the operating system disk cache in addition to the database cache.
While the operating system disk cache may improve performance in some cases, in general better performance is obtained without this option, using the database cache only.
If the server is running on a dedicated machine, you should not use the -u option, as the database cache itself is generally more efficient. You may want to use the -u option if the server is running on a machine with several other applications (so that a large database cache may interfere with other applications) and yet IO-intensive tasks are run intermittently on the server (so that a large cache will improve performance).