All of a sudden yesterday my MacBook decided it needed to spin the fan up to such a speed that I thought it was trying to take off. Not only did this seem a little strange, but it was also darn noisy and annoying.

I tried all the usual, like giving it a reboot and even reseting the power management controller, but as soon as it booted back up, the fan kicked back off again like Airwolf in a hurry.

Using iStat Pro I could see that the processor was running fairly warm, and the fan was booting around at close to 7000rpm – not normal.

Now, I’m running 10.5.5, which I have been for some time now with no problems, and it struck me as an odd thing to suddenly occur, so I checked over the processes to see what was kicking off.

Ordering the processes by CPU usage it was clear we had a winner – ATSServer. So here’s the obvious question, what the hell does that do, and why was it doing it quite so much?

A quick consultation with the Oracle told me the ATSServer, part of Mac OS X 10.5, is “a system daemon which provides font management and processing”. OK, but why is it working so hard?

Well apparently the ATSServer also plays a part in the Spotlight indexing, particularly when it’s indexing PDFs. Bamm! Hang on a minute, I’ve just added nearly 3GB of PDF files to my local disk, could this be the problem?

Another browse around the interweb and it seems the world is littered with people whose ATSServer process is causing havoc because of a big pile of PDFs. The long and short of it is that Spotlight was trying to index the contents of the PDF files and because there were so many of them it was causing the process to go mental.

There are two solutions to this problem. 1) leave it be, and if your Mac doesn’t take off, eventually it will finish indexing the files and it will return to normality, or 2) open the Spotlight preferences and add the directory with the PDF files in to the privacy list, meaning they will not be indexed. I opted for the later, and within a minute the fan had stopped. Magic.

A big shout has to go out to Martijn Bleeker who highlighted this very issue on his blog yonks ago, and which I stumbled upon today.