IntelliJ and Garbage Collection

I recently read the article about garbage collection (here) and decided to tweak my IntelliJ settings.

I am using IntelliJ 6.0.2 and JDK 1.5.0_08.

I ended up with the following settings:

-Xms256m
-Xmx512m
-XX:MaxPermSize=200m
-XX:MaxGCPauseMillis=10
–XX:MaxHeapFreeRatio=70
-XX:+UseConcMarkSweepGC
–XX:+CMSIncrementalPacing

Let’s explain them:

Heap size

-Xms256m
-Xmx512m

The more the better…

Perm size

IntelliJ likes a lot of memory for caching references and class meta information. That is why we need to make sure that cache is not purged. Cache is stored in “Old Generation” space which size is determined by the following option

-XX:MaxPermSize=200m

200m is good for the size of project I am using. General rule is to observe memory indicator after using find symbol option with include non project files selected. If it doesn’t move you have chosen enough memory.

Maximum Pause

-XX:MaxGCPauseMillis=10

We ask GC to pause the application for no more then 10 milliseconds.

Proportion of free space

-XX:MaxHeapFreeRatio=70

We ask GC to kick off when more than 30% of memory is occupied, so when we start compilation GC will not interfere because it will be enough memory free.

Concurrent Mark-Sweep (CMS) Collector

-XX:+UseConcMarkSweepGC

We want GC to run in parallel with other threads without freezing the application. This option doesn’t stop GC from freezing the application but it reduces it significantly.

Incremental Mode

–XX:+CMSIncrementalPacing

We don’t wont to freeze the application so we do GC incrementally with breaks so the application can take a breath. We use Pacing so GC can learn how to use CPU based on application CPU usage.