{"id":1016,"date":"2026-09-01T09:29:54","date_gmt":"2026-09-01T09:29:54","guid":{"rendered":"https:\/\/bestdedicatedwebhostingserver.com\/blog\/?p=1016"},"modified":"2026-10-16T22:03:11","modified_gmt":"2026-10-16T22:03:11","slug":"minecraft-modpack-dedicated-server-ram-jvm-tuning","status":"publish","type":"post","link":"https:\/\/bestdedicatedwebhostingserver.com\/blog\/minecraft-modpack-dedicated-server-ram-jvm-tuning\/","title":{"rendered":"Modded Minecraft JVM Tuning: Heap Sizing and GC Flags for 20 TPS at 80 Players"},"content":{"rendered":"\n

Modded Minecraft is one of the hardest workloads a single-threaded-biased Java process can face. A pack like All the Mods 10 or GregTech: New Horizons will demand 8-14 GB of heap for the server process alone, and the garbage collector will run thousands of times per hour while the world tick loop tries to hold 20 TPS. Get the JVM flags wrong and you will see 200-400 ms GC pauses that players feel as rubber-banding, block-break lag, and mob desync. This guide covers the JVM configuration that actually matters for a bare-metal Minecraft host: heap sizing, garbage collector selection, and the flags that keep allocation young and pauses short.<\/p>\n\n\n\n

Start With Real Heap Data, Not Guesswork<\/h2>\n\n\n\n

The most common modded server mistake is over-allocating heap. A server owner with 64 GB of RAM often reflexively assigns 32 GB to the JVM. That is almost always wrong. A larger heap means longer GC pauses because the collector has more dead objects to sweep, and old-generation collections scale in duration with live set size, not free space. For most 1.20+ modpacks, the live set after warm-up sits between 3 GB and 7 GB, so a 10-12 GB heap is plenty even for 40-60 concurrent players on a pack with 300+ mods.<\/p>\n\n\n\n

Measure before you size. Run the server for a full day of normal activity, then inspect the GC log. With G1GC enabled, -Xlog:gc*:file=\/var\/log\/mc\/gc.log:time,uptime,level,tags:filecount=5,filesize=20M<\/code> gives you rotation and timestamps. Look at the post-collection live set \u2014 under G1 it appears as the “used” figure right after an “Pause Young (Mixed)” line. Set your -Xmx<\/code> to roughly 2x that live set, and set -Xms<\/code> equal to -Xmx<\/code> so the heap never resizes mid-tick.<\/p>\n\n\n\n

G1GC Remains the Right Default in 2026<\/h2>\n\n\n\n

For modded Minecraft on modern Java (17+), G1GC is the correct collector. It is generational, region-based, and lets you cap pause time explicitly. ZGC and Shenandoah offer single-digit-millisecond pauses, but they achieve that by allowing concurrent heap compaction that competes with your simulation thread for CPU \u2014 and Minecraft is already CPU-starved on the tick loop. On a dedicated box where you want the game thread to have the least scheduling noise possible, G1 with a tight pause target beats a “better” collector that steals cycles.<\/p>\n\n\n\n

A sane starting command line for a 12 GB heap on a 16-core bare-metal node looks like this: java -Xms12G -Xmx12G -XX:+UseG1GC -XX:MaxGCPauseMillis=130 -XX:G1HeapRegionSize=16M -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=45 -XX:TargetSurvivorRatio=90 -XX:G1MixedGCLiveThresholdPercent=85 -XX:+ParallelRefProcEnabled -XX:+AlwaysPreTouch -jar server.jar nogui<\/code>. The AlwaysPreTouch<\/code> flag touches every heap page at startup so the OS does not fault pages in during play, and the enlarged young generation keeps most short-lived block and entity objects from ever reaching the old generation.<\/p>\n\n\n\n

Sizing Heap to Cores and Modpack Weight<\/h2>\n\n\n\n