Permissions Repair

I recently got into a fairly heated debate on one of the Apple fora about the value of Disk Utility's Repair Permissions.

Specifically, someone suggested the repairing permissions was necessary before and after installing any patches, and could be the fix for application slowness.

Madness.

Utter madness.

Permissions are purely about files and directory access. You either have permission to open the requested file in the manner in which the application requests or you don't. The OS doesn't say - hey, I know, you've not got the right permissions, so I'll make you wait a bit, then grant you access. No, it returns EACCES straight away.

I see repair permissions being suggested as fixes for any weirdness that people can't find an instant explanation for, when, in reality, the only time you should need to repair permissions is if you're seeing permission denied in log files or similar behaviour.

Repairing permissions is very similar to pkgchk -f on Solaris. I don't recall ever recommending a customer should run this.

I worry that much of the "Windows" mentality of utilities being produced to do things that you expect the OS to do (such as tidying up thumbnail caches, or cleaning up the registry, or protecting against viruses, etc) is spreading to the Mac and even Linux world.

The other claim that was made in this same thread was that writing to large files was significantly slower than writing to small files. Apparently, this was because you had to read the file into memory and cache it before you could write to it.

What?!!!!!!!!!!!

Why the hell would you read a file into memory just so you can then write to it? It's possibly the most ludicrous statement I've ever heard.

All that happens is you open the file, get a file descriptor, fstat it, then write the data. Surely anyone who's spent 5 minutes around any flavour of UNIX should know this?