Quick Look, Transmission, and fans

First, readers are reminded that when some process cranks up and starts taking over your computer's ability to get anything done - a phenomenon often signalled, especially on a portable, by the noise of the fans whirring up, to keep those overworked logic board components cool - you can usually finger the responsible party by opening Activity Monitor (in the Utilities folder). Switch the pop-up menu to All Processes, if necessary, and then click on the CPU column header so that processes using the highest percentage of your CPU(s) come to the top. Taking 10% or 20% of the CPU is fairly normal, but if a process is using 70% or more of the CPU, and if it does this persistently, you might suspect that not all is well.

With that out of the way, turn your attention to this blog entry and accompanying screen shot. As the author says, the fans are running hot because the Quick Look Server process is taking up way too much of the CPU, as shown in the first line of the screen shot. It's not hard to guess what the Quick Look Server does; it's probably the process responsible for keeping track of Quick Look "generators" on your computer. The "generators" are consulted whenever you ask to view a Quick Look preview. (See also our earlier coverage of Quick Look previews and how they come into existence.)

The clue as to why the Quick Look Server is being overworked, however, seems to lie in the second line of the screen shot: the application Transmission is also running. It appears to be Transmission itself that is prodding the Quick Look Server into excessive action. This hypothesis is also raised over on the Transmission forum.

It is not clear whether the cause is, as one user suggests, that the Quick Look Server is "trying to index the bittorrent files while they are downloading". It isn't entirely obvious what Quick Look Server would be "indexing"; is it hunting for "generators"? Or is it rather, perhaps, Transmission itself that interacts incorrectly with Quick Look? In any case, readers might want to be wary of Transmission until these issues are ironed out; whatever's going on, this behavior can't be right, and Transmission seems to be responsible for it.

By the way, researching this story, we discovered that you can easily obtain a conspectus of all "generators" that the Quick Look Server knows about, by typing the following into the Terminal:

qlmanage -m

The output tells you what generators you've got, listing, for each one, where it is installed, and what kind of document it understands (couched as a Uniform Type Identifier, or UTI). For example, Quick Look knows how to preview a font file (UTI "public.font") because of a generator built into the QuickLook framework. But it knows how to preview a Pages document (UTI "com.apple.iwork.pages.pages") because, if you have the current version of Pages, an iWork generator has been installed into /Library/QuickLook.

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