Fix "java.lang.OutOfMemoryError: Java heap space" on a Minecraft server

The first two are the usual ones. Both mean the same thing for you: the data the server keeps is bigger than its heap.

When we set up a server, the panel gives Java a heap a little below the memory of the plan. The rest of the plan's memory is for what Java needs outside the heap: its own code, threads and network buffers. The margin is 15% of the plan, at least 768 MB and at most 2 GB.

You do not set the heap yourself; the Startup card in Settings only chooses the Java version and the start file. How much RAM a Minecraft server needs explains why a heap the size of the whole plan would make the server crash without a line in the log.

1. Open the Overview tab and click Memory in the Performance card. Pick 24 hours or 7 days.
2. Look at the moments the server crashed or froze. A line that climbs to the top and stays there points at memory.
3. Open the Console tab. The Live resources card shows memory now, against the plan.
4. When the output shows an OutOfMemoryError, a strip on the Console tab says "Your server ran out of memory in the output above."

After a crash with this error, the Server health card on the Console tab can show why the server stopped last time, with the plugin or mod that was busy when memory ran out, if the log names one.

Every loaded chunk lives in the heap with its blocks, entities and block entities. More chunks are loaded when the view distance is high, when players are spread out, and when chunks are kept loaded by plugins, spawn chunks or chunk loaders in modpacks.

• Lower View distance (chunks) in Settings to 8, and Simulation distance (chunks) to 6. Save and restart.
• Pre-generate the world so exploring does not create new chunks that pass through memory.
• On modded servers, look for chunk loaders that players placed and forgot; each keeps its chunks in memory all the time.

Every mod loads its own code, recipes and data into the heap before a single player joins. A large modpack can use most of the heap at idle.

1. Start the server with nobody online and wait a few minutes.
2. Read the memory on the Live resources card.
3. If idle memory is already above two thirds of the plan, there is not enough room for players. Remove optional mods you do not use, or move to more memory.

The memory a pack needs is usually on its own page; install a modpack and the modpack pages list it for the packs we cover.

A leak is a plugin or mod that keeps data it no longer needs, such as a list of every player who ever joined, or every block a player ever broke. Memory then grows slowly until it runs out, often after a day or two of uptime.

1. On Paper and Purpur, type spark heapsummary in the console shortly after a restart, and again a few hours later.
2. Open both reports and compare. A class with a plugin or mod name that grew a lot points at the leak.
3. Update that plugin or mod. Leaks are often fixed in a newer version.
4. If there is no fix, remove it or look for an alternative.

Until it is fixed, a daily restart clears the heap before it fills up. Schedule automatic restarts shows how.

• Huge mob or item farms with thousands of entities in loaded chunks. Each entity takes memory. Find them with paper entity list on Paper.
• Large WorldEdit operations, such as copying or replacing millions of blocks at once. Work in smaller pieces, or use FastAsyncWorldEdit.
• Big maps with many item frames, such as image walls. Each map holds its own data.

If the memory sits at the top during normal play, after you lowered the view distance and checked for leaks, the server needs a larger plan. You cannot change the plan in the panel yourself. Contact support, every day from 07:00 to 23:00 Central European Time, or order a larger server on the configurator and move your world over.

More memory does not fix a leak; it only makes the server run longer before it fills up. Check for a leak first.