Unfortunately, it seems to be about the same with 4.1 on Lion and SL. I held off until very recently to upgrade to Lion. I will be holding off on upgrading to ML for a long time as well.
Pretty clearly Lightroom 4.X needs more hardware resources than LR 3.X—but I suspect the real source of the performance issues many of us have been experiencing is inefficient memory management in recent versions of OS X (persuasively recounted here
) that have, at least through the 10.7 release, not been addressed, or even acknowledged, by Apple.
I did some performance monitoring after experiencing LR 4 sluggishness—which was especially apparent after a roundtrip to Photoshop—and it was clear the operating system was not performing appropriate memory clean-up procedures (known in the trade as “garbage collection”) for inactive processes. This is really odd, because UNIX has always been extremely good at managing memory and OS X is derived from a well-respected UNIX variant, albeit a rather old one.
My own hunch is that this probably happened when Apple migrated from a 32-bit to a 64-bit code base. But whatever the cause, the result is that OS X seems to need a lot more physical memory than it should. I don't claim my tests were exhaustive—or even, frankly, very rigorous—but if you're going to keep a lot of processes running, I think a good metric would be 8 GB of RAM per core
. So 16 GB on a dual-core machine and a whopping 96 GB on a 12-core machine. For most if not all Apple hardware, that will mean buying third-party memory upgrades since Apple doesn't provide memory options for the maximum amount of RAM its products can address.
Another option, which helps quite a bit in my experience, is to kill idle processes. When you stop actively using a program in OS X, by default it continues to execute in the background. This shouldn't matter—and doesn't on other UNIX systems I'm familiar with—because the operating system should reclaim all but a very tiny amount of the physical memory the process was using when it was running in the foreground. Since OS X doesn't do that very efficiently, you can force the application to relinquish it's entire virtual memory allocation by using the operating system's "Quit" command. For example, if you launch Photoshop from Lightroom to do some pixel editing involving multiple layers, Photoshop will consume a huge amount of memory space. If you explicitly "Quit" Photoshop when you're finished with it (after saving your PSD file, of course) instead of clicking on the red button at the top of the PS window, the physical memory previously allocated to Photoshop will immediately become available again for Lightroom to use.
Apple really ought to fix this. I know many people have contacted the company in an attempt to document the problem, but as far as I have been able to determine Apple has never responded to any of them.
The good news, of course, is that if you stuff enough RAM in your Mac, the memory starvation will go away. (The bad news is that will inevitably only make the next bottleneck apparent, but that's the nature of performance tuning on every computer I have ever used.)