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sync-chunk-writes

To turn on synchronous chunk writes, go to server.properties and change the line to:

sync-chunk-writes=true

Or, to turn it off:

sync-chunk-writes=false

Default value: true

Section titled “Recommended starting value”
sync-chunk-writes=false

ONLY do this if you take frequent backups of your server! Data corruption is possible with this setting set to false.

What is sync-chunk-writes?

Section titled “What is sync-chunk-writes?”

When a chunk’s data is modified, the server needs to save that data to disk so that it can load it back again later. We’ll refer to that as a “chunk write”.

We have two options for when we can perform chunk writes:

  • Synchronous chunk writes: the server will pause and wait for the chunk write to finish before continuing with other tasks.
  • Asynchronous (non-sync) chunk writes: the server will continue with other tasks while the chunk write happens in the background.

The benefits of asynchronous chunk writes

Section titled “The benefits of asynchronous chunk writes”

Async chunk writes (i.e. sync-chunk-writes=false) have the benefit of not pausing the server while waiting for chunk writes to finish.

When the server auto-saves or loads/unloads chunks, this option is great for performance, because it lets the server continue what it’s doing and write the chunk to the disk in the background.

This helps avoid lag spikes when chunks are loaded/unloaded or during saves.

Short answer: sync-chunk-writes=false is generally better for performance.

The benefits of synchronous chunk writes

Section titled “The benefits of synchronous chunk writes”

Sync chunk writes (sync-chunk-writes=true) are much safer.

With the option set to false, if the server crashes or is force stopped while chunk writes are happening in the background, those chunk writes may not finish properly. This can lead to world corruption, missing blocks, and other issues.

If you set it to true, though, the server will always wait for chunk writes to finish before the server can do anything else. This reduces the risk of world corruption.

So in short, sync-chunk-writes=true is generally safer.

Which should you choose?

Section titled “Which should you choose?”

If you take frequent backups of your server:

  • You can safely set sync-chunk-writes=false for better performance, just restore a backup in the rare case that something goes wrong.

If you don’t take frequent backups of your server:

  • It’s safer to set sync-chunk-writes=true to reduce the risk of world corruption. The performance impact is usually minimal unless you have a very slow disk.