A game server might have a good CPU, lots of RAM and yet there will be lags, freezes, late responses, or even virtual or real world teleporting. Fault is not necessarily the hardware. Bad memory management definitely can impact server performance.
One of the most typical reasons for these lag spikes is garbage collection (GC), which is performed by the JVM.One of the most frequent causes of these lag spikes is garbage collection (GC) done by the JVM. The server might be suspended for a few seconds during the garbage collection of unused objects by Java. A 500ms delay could be noticeable in an intense multiplayer game where everything must be done in a timely manner.
Fortunately, the pauses can be lessened by tuning the garbage collection in Java. The newer collectors (g1gc, zgc) can provide better memory management and stability for the server. Administrators can minimize lag spikes and provide smoother gameplay with the proper JVM settings.
Why Garbage Collection Causes Lag Spikes in Game Servers
In a java game, objects are continuously added and deleted during the game. Temporary objects are created inside the Java heap when movements are made, when entities are updated, chunks are loaded or unloaded, inventory is accessed, or the world is triggered.
As these unused objects build up, garbage collector begins garbage collection. In some GC operations, Java kills the application threads, so as to safely manage memory.
If the game server is operating at 20 ticks per second, then there’s just 50 milliseconds for each tick. A 500ms garbage collection pause allows for the ability of missing multiple ticks at a time.
Players may notice symptoms like:
- Sudden server freezes
- Delayed player movement
- Block placement delays
- Entity movement issues
- “Server can’t keep up” warnings
- Random lag spikes during high activity
Not uncommon to have enough hardware and lack the software. Efficiently using memory or wrong JVM configuration is often the source of the problem.
Good java memory management practices for games involve minimizing the amount of unnecessary allocations, choosing the right garbage collector and observing the memory behavior rather than adding to the RAM.
Understanding Java Garbage Collectors: G1GC vs ZGC
There are many garbage collectors available in Java, two common garbage collectors used for modern game servers are G1GC and ZGC.
Both collectors have the goal of cleaning unused memory during operation without affecting the performance of the application, albeit in different ways.
G1GC: The Traditional Choice for Game Servers
Since it has a good balance between performance and garbage collection, it has been widely used for Java game servers because of that, G1GC (Garbage First Garbage Collector) is used.
G1GC doesn’t clean the whole heap, but rather breaks it up into smaller regions and cleans some regions that contain more garbage.
There are many Minecraft server admins who use optimized JVM settings, some of which are set using Aikar’s flags.
These settings change the way memory is used, the timing of garbage collection and how the heap is managed, which should improve the performance of the game.
This is the widely-used aikars flags minecraft tuning method, which is suitable for a large number of servers, particularly those that run with moderate workloads and are limited in memory.
Advantages of G1GC:
- Good overall performance
- Lower CPU overhead compared to some low-latency collectors
- Works well with medium-sized heaps
- Mature and widely tested
- Suitable for many Minecraft servers
In cases where the server’s heap is large, there are heavier workloads, or increase in the number of objects being created, however, G1GC can still cause pauses that are noticeable.
ZGC: Designed for Low Latency Gaming
To get the best of both worlds, a new garbage collector named ZGC (Z Garbage Collector) was developed for applications requiring a high-speed response rather than maximum throughput.
Unlike traditional collectors, ZGC can do most of the memory clean up work concurrently while the application is running. This will make the game server’s pause times significantly shorter.
This will make the game server’s pause times significantly shorter.
ZGC can help offer smoother performance on large servers with lots of players, huge worlds or extensive plugin usage, as it minimizes the frequency of long periods of garbage collection interruptions.
Java 21 and later have enhancements, including Generational ZGC, which is a more efficient garbage collector for short-lived objects.
Benefits of ZGC:
- Extremely low pause times
- Better consistency during heavy workloads
- Suitable for large memory servers
- Helps reduce sudden lag spikes
The zgc low latency game server flags approach is becoming popular for high-performance gaming environments where predictable response time is important.
ZGC vs G1GC Benchmark Comparison for Game Servers
The best garbage collector depends on your workload, available hardware, and performance requirements.
A simplified comparison:
| Feature | G1GC | ZGC |
| Main Goal | Balanced performance | Minimum pause time |
| Memory Usage | Lower | Slightly higher |
| CPU Usage | Usually lower | Higher due to concurrent work |
| Large Heap Performance | Good | Excellent |
| Pause Time | Moderate | Extremely low |
| Best For | Medium servers | Large low-latency servers |
When testing in practice, ZGC may have very short pause times even with bigger memory allocations, while G1GC may not have such short pause times, even with smaller memory allocations. G1GC offers a little higher raw throughput but when it comes to consistency of latency, ZGC is likely to be the better of the two options.
ZGC, for instance, may be better for a server that has a 16GB+ heap that is running a lot of plugins or complex worlds, than to save a few CPU cycles, and have large pauses.
How to Fix Java GC Lag Spikes on a Game Server
If lag is becoming a regular occurrence on your server it may not be enough to merely change the garbage collector. It is necessary to undertake a proper tuning process.
1. Check Your Current Memory Usage
Before changing JVM flags, monitor:
- Heap usage
- GC frequency
- Pause duration
- CPU consumption
- Player activity during lag events
You can use some tools such as Java Flight Recorder (JFR), Spark profiler and garbage collection logs to determine if the issue is related to garbage collection.
When configuration of JVM becomes a guess, it’s because there was no measurement done.
2. Use Proper Heap Size Settings
The provision of unlimited memory to Java is not all good.
Almost all server memory being allocated to Java is a common error. Memory is also needed by the operating system, plugins and other services
Leave a sufficient amount of memory outside the Java heap.
For example:
- Small server: 4GB-8GB RAM
- Medium server: 8GB-16GB RAM
- Large multiplayer server: 16GB+ RAM
The proper heap size will minimize unnecessary garbage collections and avoid memory pressure.
3. Choose G1GC or ZGC Based on Workload
There is no single configuration that works for every server.
Use G1GC when:
- Your server has limited RAM
- CPU resources are restricted
- Player count is moderate
- You need balanced performance
Use ZGC when:
- Your server has plenty of RAM
- You run large worlds or modpacks
- Players require stable latency
- GC pauses are causing visible lag
A small VPS with limited CPU resources may not benefit from ZGC because the collector needs additional CPU capacity for background memory management.
Recommended JVM Tuning Approach
Do not copy arbitrary JVM parameters from the web, fine-tune for your server’s operation.
Aikar-style configurations are typically used with G1GC configurations to make GC work as desired with Minecraft workloads
Simpler configuration may be more desirable for ZGC users since many of the memory operations are handled efficiently by ZGC.
Example considerations:
- Keep Xms and Xmx values the same
- Use modern Java versions
- Avoid unnecessary JVM flags
- Monitor before and after changes
- Test changes during realistic player loads
The goal is not maximum benchmark numbers. The goal is stable gameplay.
Hardware Also Plays an Important Role
The best software tuning that can be done will not correct bad infrastructure.
A game server requires constant CPU performance, quick storage and adequate resources. When other users are using resources that are shared, it can cause unpredictable performance.
For demanding gaming workloads, choosing a server dedicated low cost solution can provide better control over CPU, RAM, and storage performance. Dedicated resources help maintain stable tick rates, reduce performance fluctuations, and provide a more predictable environment for servers running heavy Java workloads.
Common Mistakes During Java GC Tuning
Here are some common issues that administrators will encounter, due to using old or wrong settings.
It’s easy to make these errors, such as:
Using Too Many JVM Flags
Highlighted flags don’t necessarily mean good performance. Wrong-associations will lead to unusual behavior.
Increasing RAM Without Optimization
As the amount of memory increases, the lag will not automatically get less. Even if the applications are well configured they still can generate too much garbage.
Using ZGC on Low Resource Servers
The performance of ZGC is optimum when ample CPU and memory resources are available.
Ignoring Plugins and Game Logic
Garbage collection is not the only aspect of performance. Lags can also be caused by poorly optimized plugins, scripts or game mechanics.
Best Practices for Smooth Java Game Server Performance
To maintain stable performance:
- Keep Java updated
- Monitor GC logs regularly
- Select the collector based on workload
- Optimize plugins and server settings
- Avoid unnecessary object creation
- Use fast storage solutions
- Maintain sufficient CPU resources
Optimising a server involves software optimisation and a reliable system.
FAQs About Fixing Java Garbage Collection Lag in Game Servers
Q: What causes Java garbage collection lag spikes on game servers?
If the JVM pauses its server in order to remove unused memory objects, this is the reason for java GC lag spikes. These pauses can be extended due to heavy workloads, plugins and improper memory settings.
Q: Is G1GC or ZGC better for Minecraft and Java game servers?
G1GC is better for all servers except for large servers that can’t afford any major latency issues and smooth play.
Q: How can I fix Java GC lag spikes on my game server?
Look at GC activity and optimize JVM, manage memory properly and plan to remove high-performance consuming plugins; to decrease garbage collection delays.
Q: Are Aikar’s flags still useful for Minecraft server tuning?
Aikar’s flags remain popular to optimize Minecraft on with G1GC. They can be used to increase memory management but must be applied as per your server’s workload.
Q: Does adding more RAM solve Java garbage collection problems?
This can be ameliorated by having more RAM, but is not a solution for all problems. Appropriate Java tuning, optimized software and hardware are also needed.
Wrapping Up
In multiplayer game servers, Java garbage collection is an important factor in helping to ensure a smooth operation. Although GC pauses are a standard part of Java memory management, they can cause lag spikes and impact the player experience if they are not configured correctly.
If you are using a server for any type of workload, choosing between G1GC and ZGC depends on your requirements. For most Minecraft and Java servers, G1GC is a reliable option, while larger servers where latency and response times are more critical can benefit from ZGC.
Before applying advanced JVM tuning, having a properly configured Minecraft server environment is equally important. You can learn more about setting up and optimizing a Minecraft server in this Minecraft Server Hosting Guide.
There is more to Java garbage collection tuning than simply changing JVM flags. Regular monitoring, proper memory allocation, optimized settings, and reliable server resources all contribute to better performance.
