I've just updated my IntelliJ IDEA to latest 12.1 version and I found my laptop CPU usage become 100% from time to time, monitor the progress manager I found IDEA fork an new Java process regularly and it runs for several tens of seconds and shutdown. During that time the CPU usage is close to 100%:

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I use IntellJ too, It has never eaten 100% cpu, the problem whether is that there are too many moduls in your project? maybe help you. P.S. Are you from China? – Hunter Zhao Apr 05 '13 at 03:45
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This may be an effect of automatic [external build enabled](http://img189.imageshack.us/img189/3550/20121206235318.png). If you are using Scala, it will also run compilation in background. – CrazyCoder Apr 05 '13 at 09:34
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I am not using Scala. All pure Java. – Gelin Luo Apr 05 '13 at 09:41
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@CrazyCoder, hello! It seems that for IDEA13 settings page was changed. How to disable automatic external build now in v.13.1? thank you! – java_newbie Oct 23 '14 at 12:15
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@java_newbie this question is obsolete. If you have problems, contact support with the [CPU snapshot](https://intellij-support.jetbrains.com/entries/29983118). You can't disable external build in IDEA 13. – CrazyCoder Oct 23 '14 at 12:17
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This is not a question. – Glenn Bech Oct 21 '16 at 11:26
4 Answers
Chances are the external build mentionned by @CrazyCoder compiles your project automatically when you make changes to your source files. If it annoys you too much, you can disable automatic compilation in File > Settings > Compiler > Make project automatically
(uncheck the box).

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No, this external build system was introduced in IntelliJ 12, but it may have changed a little bit in 12.1. I disabled this option in 12.0 because mu current laptop doesn't like it very much :) – Bastien Jansen Apr 12 '13 at 07:27
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there's no such checkbox in IDEA13, so how do you deal with it now? – java_newbie Oct 23 '14 at 12:19
I had the IDEA 12 process itself (not a forked Java) occupy 100%, and respond very slowly to keypresses, navigation, etc.
Eventually I resolved this by cleaning out the cache, prefs, Application Support dir, etc and uninstalling/reinstalling IDEA 12. You have to reinstate your preferences and let Idea reindex your projects (due to removing its cache) - but this shouldn't take long.
Here's a list of some places to clean on OS X (slightly out of date for IDEA 12, but a useful starting point).
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This worked for me with IDEA 13 on OSX Mavericks. Thank you! Made a huge difference. Well worth the effort to go through the re-install. – gstathis Apr 21 '14 at 14:37
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1File --> Invalidate Caches / Restart .. did the trick for me. Before that the CPU usage was upwards of 60% and restarting IntelliJ alone did not help. – Sanjiv Jivan May 04 '15 at 19:47
I am using IntelliJ 13 Community Edition and have found this problem on Linux. It my case it is the Intelli JBehave plugin causing these issues.
When opening a dialog the CPU usage of the Java process drops right back to 5 to 10% percent. When disabling the plugin the same is true.

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I am having this same issue with IDEA 13 Ultimate on Linux Mint 17 (insane, 100% load which drops to 5% when a dialog is opened). I can't find a plugin called "JBehave" or "Behave" though. Are you sure it is called like this? – sola Sep 02 '14 at 20:45
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Goto Home Folder then Navigate to .IntelliJIdea13\config\options
Edit the file "project.default.xml" Change the VM_PARAMETERS Xmx and Xms as follows
It decreased the CPU usage to 50%

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