in reply to
unlink : reclaim inodes, etc.?
I don't know UFS, and I don't know the filesystem internals well enough to give an educated answer.
However, I experienced with all filesystems I tried a slowdown after some time.
Therefore I try to put directories with heavy read/write access into separated partitions/filesystems.
At my Linux (Gentoo) workstation there's a directory with >150000 files and around 43MB, which is updated daily. (It contains the software package information).
In order to get some more performance, I'm using a virtual filesystem kept in the memory, which is loaded and saved into a single file at the boot/shutdown process.
In your case, if performance is important, I could also think of two partitions, which are regulary copied/formatted.
(dev/part1 mounted at /mnt/mountpoint)
mount /dev/part2 /mnt/tmp
cp -a /mnt/mountpoint /mnt/tmp
mount /dev/part2 /mnt/mountpoint
That's, however, just a suggestion to start from and possibly not practicable for you, I'm really very interested how you/others solve this problem.