{"id":8157,"date":"2026-10-10T20:00:00","date_gmt":"2026-10-10T20:00:00","guid":{"rendered":"https:\/\/cybrancee.com\/blog\/?p=8157"},"modified":"2026-10-10T19:54:32","modified_gmt":"2026-10-10T19:54:32","slug":"what-is-garbage-collection-in-minecraft-servers","status":"publish","type":"post","link":"https:\/\/cybrancee.com\/blog\/what-is-garbage-collection-in-minecraft-servers\/","title":{"rendered":"What Is Garbage Collection in Minecraft Servers?"},"content":{"rendered":"\n

Your server runs fine for ten minutes. Then everyone spikes for half a second, TPS drops, and everything snaps back as if nothing happened. Most owners blame a plugin, a redstone clock, or the host. Sometimes they’re right. Most of the time, the culprit is Java’s garbage collector doing its job at a bad moment.<\/p>\n\n\n\n

Garbage collection (GC) is how the Java Virtual Machine frees memory the program no longer uses. A Minecraft server is a Java program, so every server you have ever joined depends on it. When it works, nobody notices. When it’s set up badly, it shows up as stutter that no CPU upgrade can fix.<\/p>\n\n\n\n

Here is what garbage collection actually does, which collector your server is probably running, and which flags are worth using in 2026.<\/p>\n\n\n\n

Java Garbage Collectors at a Glance<\/h2>\n\n\n\n
Collector<\/th>Pause Behavior<\/th>Status<\/th>Fit for Minecraft<\/th><\/tr><\/thead>
Serial<\/td>Single thread, pauses grow with heap size<\/td>Still ships with the JDK<\/td>Not recommended<\/td><\/tr>
Parallel<\/td>Multi-threaded, but long stop-the-world pauses<\/td>Default through Java 8<\/td>Poor fit, causes visible lag spikes<\/td><\/tr>
CMS<\/td>Mostly concurrent, shorter pauses, fragmentation over time<\/td>Deprecated in Java 9, removed in Java 14<\/td>Obsolete<\/td><\/tr>
G1<\/td>Region-based, aims for a pause target (200 ms by default)<\/td>Default since Java 9<\/td>Recommended for most servers<\/td><\/tr>
ZGC<\/td>Almost fully concurrent, sub-millisecond pauses<\/td>Production since Java 15, generational by default since Java 23<\/td>Large heaps, needs spare CPU<\/td><\/tr>
Shenandoah<\/td>Concurrent compaction, very short pauses<\/td>Production since Java 15, generational mode is a product feature in Java 25<\/td>Alternative to ZGC, less tested on Minecraft<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

What Garbage Collection Actually Does<\/h2>\n\n\n\n
\"minecraft<\/figure>\n\n\n\n

Minecraft creates objects constantly: block positions, chunk data, entities, item stacks, packets. Once nothing references an object anymore, it’s garbage. The JVM finds that garbage and reclaims the memory so it can be reused. You never free memory by hand like you would in C. The collector does it for you.<\/p>\n\n\n\n

The catch is that most collection work needs the application to stop. This is called a stop-the-world pause: the JVM freezes every thread, including the main server thread, until the collector is done. The game loop runs 20 ticks per second, which gives each tick 50 ms. A 200 ms pause swallows four ticks in one go. Players see it as a hitch, and the TPS graph dips and recovers.<\/p>\n\n\n\n

Pauses should be short and rare. Aikar, the author of the flags Paper recommends, puts a healthy rate at one young collection every 10 seconds to a few minutes. Velocity’s tuning guide reports pauses under 10 ms every few minutes with its recommended G1 flags, which is very good for a game server.<\/p>\n\n\n\n

Why Minecraft Makes So Much Garbage<\/h2>\n\n\n\n

Minecraft has an extremely high memory allocation rate. Paper’s docs put it at 800 MB per second or more on a 30-player server, and most of that is short-lived data like block positions. Almost all of it dies young.<\/p>\n\n\n\n

That is why the young generation matters so much. G1 gives it roughly 5% of the heap by default, which is far too little for this workload. When the young generation is too small, G1 runs young collections once or twice per second. TPS suffers, objects get promoted to the old generation earlier than they should, and the old generation fills up faster. Aikar’s flags exist mostly to fix this one problem.<\/p>\n\n\n\n

A Short History of Java Garbage Collectors<\/h2>\n\n\n\n
\"different<\/figure>\n\n\n\n

Java’s collectors have changed a lot, and the version of Java your server runs decides which one you get.<\/p>\n\n\n\n

Serial GC is the original single-threaded collector. It has a tiny footprint, but pauses grow with the size of the heap, so it never made sense for a game server. Parallel GC came next. It uses multiple threads to collect, which is great for batch jobs and bad for anything latency-sensitive. It was the default through Java 8, and Velocity’s docs describe its long pauses as a source of unexplainable lag spikes in Minecraft.<\/p>\n\n\n\n

CMS (Concurrent Mark-Sweep) was the low-pause option for years. It did most of its marking while the application kept running, but it didn’t compact memory, so fragmentation built up over time. It was deprecated in Java 9 and removed in Java 14. If you still see CMS flags in an old start script, that script needs rewriting.<\/p>\n\n\n\n

G1 (Garbage-First) splits the heap into regions and collects them incrementally, with a pause-time goal you can set. It became the default in Java 9 and is still the default today. ZGC and Shenandoah are the newer low-latency collectors. ZGC was experimental in Java 11 and went into production in Java 15, and Shenandoah followed in the same release. Generational ZGC arrived in Java 21, became the default ZGC mode in Java 23, and the non-generational mode was removed in Java 24. Shenandoah’s generational mode went from experimental in Java 24 to a product feature in Java 25, though you still have to turn it on yourself.<\/p>\n\n\n\n

Which Collector Is Your Server Using?<\/h2>\n\n\n\n

Probably G1. Minecraft 1.17 and later need Java 16 or newer, and G1 is the default on all of those. Minecraft 26.1, released on March 24, 2026, was the first version to require Java 25, and G1 is still the default collector there.<\/p>\n\n\n\n

Servers on the old 1.8 to 1.16 versions often ran on Java 8, which meant Parallel GC unless someone overrode it. That is a big part of why Aikar’s flags became so popular.<\/p>\n\n\n\n

The server software itself doesn’t change any of this. Vanilla, Spigot, Paper, Fabric, Forge, and NeoForge all run on whatever JVM launches them, so the collector depends on your Java version and your startup flags. Paper publishes the most complete flag documentation. Velocity’s docs recommend G1 with their own flag set. BungeeCord has no official GC guidance, so most owners borrow the same G1 settings from community advice.<\/p>\n\n\n\n

How to Tell If Garbage Collection Is Hurting Your Server<\/h2>\n\n\n\n
\"out<\/figure>\n\n\n\n

GC problems have a recognizable pattern. TPS dips at regular intervals instead of randomly. The console prints “Can’t keep up!” even though the CPU isn’t maxed out. Heap usage sits near 100% all the time, or the server crashes with an OutOfMemoryError when a lot of players explore at once.<\/p>\n\n\n\n

To confirm it, turn on GC logging. Paper’s docs give this flag for Java 11 and newer:<\/p>\n\n\n\n

Bash<\/span>