Many server owners have encountered issues with high memory (RAM) usage, even when there are no players online. Many have also noticed that their server’s memory usage sits right below the memory limit, even when the server is sitting idle. This can be confusing, because it can make it look like there is something wrong with the server. However, this is actually how the Java Virtual machine handles memory.
An example
If you’ve been managing a Minecraft server for some time, you’ve likely observed that even when no one is online, the memory use seems to stay high. This could be concerning, particularly if you just upped the RAM on your server in the hopes that it would fix the issue. You’re not alone, and there’s a solid reason why, so don’t worry.
JVM & GraalVM Explained
Here is an example one of our users faced: after upgrading from 16 GB to 20 GB of RAM on a server, I noticed that the memory usage didn’t go down like I expected. In fact, it just filled up more. Even when no one was playing, the server used almost all of that 20 GB. It turns out that this is actually normal for Minecraft servers, especially when they use something called the Java Virtual Machine (JVM), specifically GraalVM.
GraalVM is designed to take as much memory as it can. It doesn’t mean the server actually needs all that memory, but it holds onto it “just in case.” It’s like setting aside a lot of space, even if you’re only using part of it right now. So, it looks like your server is using all the RAM, but it’s mostly reserving it for potential future use.
The reason GraalVM does this is to avoid the extra work of constantly adjusting memory. If your server had to keep adding and releasing memory every time players join or leave, it would slow things down. By keeping a big chunk of memory at the ready, the server can run more smoothly when there’s a spike in activity. So, it’s actually a good thing, even though it might look a bit strange if you’re watching your memory usage closely.
Using Spark
If you want to see what’s actually going on, there’s a tool called Spark that can help. Spark gives you detailed reports on how much memory and CPU your server is really using at any moment. It’s a great way to check whether mods or plugins are using up more memory than they should or if everything is running as expected.
You can find more about Spark and how to use it by checking out their documentation.
Conclusion
If your server seems like it’s always using up all your RAM, don’t stress—it’s just how JVM, and specifically GraalVM, works. Your server is most likely holding onto memory just to make sure it’s ready if things get busy. Most of the time, it doesn’t actually need all the memory it’s grabbing.
If you want to keep a closer eye on things, tools like Spark are your best bet.