JVM Memory Defaults

Question

What is the default Xms and Xmx settings for the Sun JVM (v 1.4*) if those values are not specified at startup?

Answer 1

From Sun's tooldocs:

-Xmsn Specify the initial size, in bytes, of the memory allocation pool. This value must be a multiple of 1024 greater than 1MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is 2MB. Examples:

           -Xms6291456
           -Xms6144k
           -Xms6m

-Xmxn Specify the maximum size, in bytes, of the memory allocation pool. This value must a multiple of 1024 greater than 2MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is 64MB. Examples:

           -Xmx83886080
           -Xmx81920k
           -Xmx80m

So 2MB and 64MB.

(The link above is for the 1.5 docs, but you can download the 1.4 docs, and they say the same thing.)

Answer 2

As documented:

• Xmx: default 64M
• Xms: default 2M

That's for Linux, but I've checked and the values are the same for Windows and Solaris too. Don't rely on that being the case for other versions or options though. In particular, the choice of server or client VM depends on operating system, at least in later versions.