large directory performance

[tridge at linuxcare.com]

The correct fix is to have a sysctl() that sets the filesystem to be
case-insensitive in the VFS layer. Unfortunately that requires kernel
modifications.

actually, even this doesn't _really_ solve the problem, it just puts
it in the kernel. Even on a fully case-sensitive system something,
somewhere, has to scan the whole directory to see if the file exists
before creating a new file. If you have thousands of files in a
directory on a MO medium and the kernel doesn't cache directories very
well then this will always be slow. A tree-based directory system
would be a big help but that would require changes in your filesystem
format.

Cheers, Tridge