How to Fix Garbage Collection Lag Spikes on a Minecraft Server

Direct answer

GC may pause gameplay, but a rising memory graph alone does not prove that garbage collection is responsible. Correlate pauses and high MSPT at the same timestamps.

Identify the failing layer

Garbage collection reclaims Java heap objects; a pause can affect ticks, but heap growth can also be normal between collections.

First checks and evidence

Record heap size, Java version and container RAM limit; verify that the process is not being killed by the OS.
Collect a spark GC report or Java GC logs where available and identify actual pause durations.

Admin diagnosis and repair

Compare the pause times with player lag reports and a spark tick-time profile.
Reduce measured allocation pressure or a misbehaving plugin before changing collector flags; change one variable and retest.

Verify the fix: Compare identical player workloads before and after the change, including pause length, MSPT and memory headroom.

Important safety note

Increasing -Xmx without host headroom can trigger swapping or an OOM kill; collector flag recipes are not universal.

References

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

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