For the task at hand we dug into the 1,024 environments we had gathered statistics from. 662 out of those had overridden the default maximum heap size by setting the -Xmx parameter. Also, 414 had felt that the permanent generation is not properly sized and had specified -XX:MaxPermSize by themselves.
We found some interesting aspects from this data:
- 70% of the heaps were sized between 512MB and 4GB
- Only 4% of the heaps were larger than this.
- Maximum heap we discovered from this dataset was 42GB
- 40% of the users specifying maximum size to the permgen set it to 256MB.
- ... but there are two guys who either are bad at maths or have done some fine-tuning and set it to 258MB
If you are interested in the whole study, then it is available in the form of a blog post.