-Xms: Initial heap size or minimum heap size?

Question

-Xms is to specify initial heap size or minimum heap size? I see differing viewpoints. Some like second answer here , say that it is for initial heap and some others say that it is minimum heap size.

Or is it that the minimum size itself is the initial size?

Answer 1

The initial heap size is the minimum heap size. It won't get smaller than the initial heap size.

From Tuning Garbage Collection with the 5.0 Java[tm] Virtual Machine :

By default, the virtual machine grows or shrinks the heap at each collection to try to keep the proportion of free space to live objects at each collection within a specific range. This target range is set as a percentage by the parameters -XX:MinHeapFreeRatio= and -XX:MaxHeapFreeRatio=, and the total size is bounded below by -Xms and above by -Xmx .

Answer 2

From running java -X:

-Xms<size>        set initial Java heap size
-Xmx<size>        set maximum Java heap size
-Xss<size>        set java thread stack size

Note that -X options are not guaranteed to exist on all VMs or behave the same on all VMs. For example -Xms could format your hard drive depending on the VM (it would not - but strictly speaking it could :-) (typing java by itself gives the help with this line: "-X print help on non-standard options").