A very technical analysis finds the G5 to be a reasonable workstation choice, but OS X fares poorly as a server solution.
The server performance of the Apple platform is, however, catastrophic. When we asked Apple for a reaction, they told us that some database vendors, Sybase and Oracle, have found a way around the threading problems. We'll try Sybase later, but frankly, we are very sceptical. The whole 'multi-threaded Mach microkernel trapped inside a monolithic FreeBSD cocoon with several threading wrappers and coarse-grained threading access to the kernel', with a 'backwards compatibility' millstone around its neck sounds like a bad fusion recipe for performance.I think they used 10.3 for testing. I wonder how the server results would look with 10.4? Apple made major challenges to the threading model.
Workstation apps will hardly mind, but the performance of server applications depends greatly on the threading, signalling and locking engine. I am no operating system expert, but with the data that we have today, I think that a PowerPC optimised Linux such as Yellow Dog is a better idea for the Xserve than Mac OS X server.