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Reading a Spark report

Install Spark, take a profile, and understand the top three lines of the result. That is where the answer usually is.

1 min readUpdated 2026-09-14Diese Anleitung auf Deutsch lesen →

Spark is a profiler: it watches what the server spends its time on and shows it as a tree.

Take a profile

  1. Install spark via the Plugins (or Mods) tab; restart.
  2. Wait for the lag to happen. In the console: spark profiler start --timeout 60. It records for 60 seconds.
  3. The console prints a link (spark.lucko.me/...). Open it.

Read it

  • Top of the page: TPS, MSPT and memory over the recording. Confirms that it lags.
  • The tree below: expand Server thread → Tick. Every line is a thing the server does per tick with a percentage. Look at the biggest percentages.
    • EntityTickList / entityTick high → too many mobs or a mob-heavy area. /spark tickmonitor shows where.
    • ChunkMap / chunk generation → players exploring. Pre-generate.
    • A plugin's package name (com.example.myplugin) → that plugin. Update, reconfigure or remove it.
    • Redstone / hopper → a machine somewhere. Paper's hopper settings help.
    • GC at the top or long Old Gen pauses in the memory graph → not enough RAM.

Shortcut

Paste the link into Kowalski: "read this spark report and tell me what causes the lag". It reads the tree and explains it in plain words, usually with the exact config change.