ZGC for Minecraft Servers in 2026: Should You Use It?
If you have chased Minecraft server lag, you have run into garbage collection. The JVM periodically pauses to clean up memory, and on a busy server those pauses show up as stutters and TPS dips. ZGC is a low-latency garbage collector that promises near-zero pauses - but it is not automatically the right choice. Here is how it really compares to the classic Aikar's flags (G1GC) in 2026.
What is ZGC?
ZGC (the Z Garbage Collector) is a JVM collector designed for very low pause times that stay flat no matter how large the heap is. It does most of its work concurrently while the server keeps running, so GC pauses are typically sub-millisecond. It shines on large heaps - think 16GB and up.
What are Aikar's flags?
For years the community standard has been Aikar's flags: a finely-tuned set of G1GC arguments that aggressively keep pauses short and predictable for Minecraft's allocation pattern. They are battle-tested, well understood, and the default recommendation for most servers.
ZGC vs Aikar's G1GC: the honest comparison
| Aikar's G1GC | ZGC | |
|---|---|---|
| Pause times | Very short, occasional small spikes | Consistently near-zero |
| Best heap size | 4-12GB | 12GB+ (really shines at 16GB+) |
| Throughput | Excellent | Slightly lower (more CPU on GC) |
| Memory overhead | Lower | Higher (needs RAM headroom) |
| Tuning | Pre-tuned, proven | Simpler flags, fewer knobs |
| Best for | Most servers, modpacks | Large-heap, low-pause-critical servers |
The trade-off: ZGC buys you flatter pause times at the cost of a bit more CPU and RAM overhead. On a small 4-6GB server, Aikar's G1GC is usually the better, more efficient choice. On a large modded server with 16GB+, ZGC can deliver noticeably smoother frame-to-frame consistency.
When ZGC actually helps
Reach for ZGC if:
- Your heap is 16GB or larger (big kitchen-sink modpacks, large player counts).
- You see periodic GC pause spikes in your timings even after Aikar's flags.
- You have CPU and RAM headroom to spare for GC overhead.
Stick with Aikar's G1GC if:
- Your server is 12GB or smaller.
- You want maximum throughput and efficiency.
- You want the most proven, community-supported setup.
Running ZGC: the flags
ZGC needs Java 17+ (use a current LTS like Java 21). A minimal, sane setup:
java -Xms16G -Xmx16G \
-XX:+UseZGC \
-XX:+ZGenerational \
-XX:+AlwaysPreTouch \
-XX:+PerfDisableSharedMem \
-jar server.jar nogui
Key points:
- Set
-Xmsequal to-Xmxso the heap does not resize. -XX:+ZGenerationalenables the generational mode of ZGC, which is the version you want on modern Java - it is far more efficient for Minecraft's short-lived allocations.- Do not mix ZGC with Aikar's G1GC flags - they are different collectors. Use one or the other.
Measure, do not guess
Whatever you pick, measure it. Run a profiler like Spark and watch your MSPT (milliseconds per tick) and GC pause graph under real load. If Aikar's flags already give you flat ticks, ZGC will not magically add TPS - GC is only worth tuning when GC is actually your bottleneck.
Hardware matters more than flags
No collector fixes weak hardware. GC tuning helps at the margins; fast single-thread CPU and enough RAM do the heavy lifting. A 16GB modpack on a slow shared core will stutter no matter the collector.
Our Minecraft hosting runs on Ryzen 9 hardware with NVMe SSD and lets you set your own JVM flags, so you can run Aikar's G1GC or ZGC and give big modpacks the cores and memory they need.
Bottom line
ZGC is excellent for large 16GB+ servers that need ultra-flat pauses, while Aikar's G1GC remains the best all-round choice for most servers up to ~12GB. Use generational ZGC on Java 21 if you go that route, never mix the flag sets, and always profile before and after.
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