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In about 50 minutes from now (it's 11:06 PM) my machine will slow down. It does this every night at the exact same time.

Is OSX indexing or what is going on and what can I do about it?

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Open up Activity Monitor and sort all processes by CPU usage. When your computer slows down, find the offending process. – NReilingh Jan 20 '11 at 22:15
up vote 2 down vote accepted

Your computer is running the periodic daily scripts. These just clean up temporary files, caches, and do other daily maintenance. You can read more about it on Apple's site here.

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Never knew about that before... thanks for providing that info! – nhinkle Jan 20 '11 at 23:25
thank you for your answer. – ThomPete Jan 20 '11 at 23:27
Nope, this isn't it; the daily (and weekly) periodic scripts don't run at midnight, they run at 3:15 am, and the monthly one runs at 5:30 am (see the Additional Information section of the linked article, or the actual launchd files in /System/Library/LaunchDaemons/*.plist). – Gordon Davisson Jan 21 '11 at 8:14
Gordon is correct, the dailies run at 03:15 each day. I know this because I set up a script that would mount my Ext. FW HDD when daily script ran, and the HDD always mounted at 03:15. – penguirl Jan 21 '11 at 9:29

If you want to make them happen when you're free to take the performance hit, type sudo periodic daily into the terminal.

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