[SOLVED] minecraft server max heap size setting ignored

[jasoncollege24]

Hi,

I'm not sure this is the right place to put this, but I was at a loss of where else to ask.

I'm trying to setup a modded minecraft server, using java-17-openjdk-amd64, on kubuntu 20.04. I have all the mods installed, and the server is ready to run. Problem I'm having is that when I set the min/max heap size, the upper limit value is being completely ignored.

For my client, on single player games (Windows) I set my max heap size to 8GB. When I try to start the server on linux, I'm using the command

java -Xms1G -Xmx8G

everything else is default, but the server reports that it's only being given 3.8GB (out of about 18GB free on the machine), which sounds like a 32bit limit.

Is there possibly something I'm missing, or doing wrong? Any help would be greatly appreciated.

[GreyGeek]

You are getting the maximum Xmx size that a 32bit Java can muster, but you are using the 64bit JVM. The problem is described here.

And, as the article points out, citing Oracle,
"Generally, the benefits of being able to address larger amounts of memory come with a small performance loss in 64-bit VMs versus running the same application on a 32-bit VM.

The performance difference comparing an application running on a 64-bit platform versus a 32-bit platform on SPARC is on the order of 10-20% degradation when you move to a 64-bit VM. On AMD64 and EM64T platforms this difference ranges from 0-15% depending on the amount of pointer accessing your application performs.”

There is nothing in Java that stops prevents the Minecraft server from using more heap space, so the limit must be built into the Minecraft server itself.

[jasoncollege24]

Yup. Looks like I somehow managed to install a 32Bit minecraft server, instead of 64, without knowing it. Thanks.