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Prune pre-merge history

Node operators using Snap sync can significantly reduce disk usage by removing pre-merge Proof of Work (PoW) block data from the local database.

Besu can prune all pre-merge block bodies and associated transaction receipts, leaving only headers and the genesis block.

warning

Besu does not currently provide a way to import pre-merge block data after pruning. If you need to restore the full pre-merge history, you can revert to the former Snap sync behaviour and download all blocks from peers by setting --snapsync-synchronizer-pre-checkpoint-headers-only-enabled=false.

Besu provides multiple options to prune the historical blockchain data:

  • Offline pruning to prune data on a stopped Besu instance.
  • Online pruning to prune data on a running Besu instance.
  • Sync Besu using Snap sync, which by default prunes the historical blockchain data.

Offline pruning​

The fastest option for pruning pre-merge blocks is to perform an offline prune. It won't prune as much data as a full resync.

  1. Ensure your Besu instance has stopped, and run the following command:

    besu --data-path=/path/to/your/database storage prune-pre-merge-blocks

    The command prune-pre-merge-blocks prunes the database using the default options.

    On completion, you'll receive the Pruning pre-merge blocks and transaction receipts completed log message. It should only take a few minutes to complete but has been known to take up to two hours on occasion.

  2. Add the --history-expiry-prune option and restart Besu to apply opinionated database garbage collection options to help free up space. You can tweak underlying garbage collection options separately if necessary.

    info

    In testing, we saw the space increased by up to 200GB before the space was finally reclaimed. We suggest waiting 24-48 hours for all the space to be reclaimed.

  3. (Optional) Remove the --history-expiry-prune option and restart Besu. This will disable garbage collection which isn't necessary after pruning has reclaimed all the space.

Online pruning​

Online pruning allows you to prune the pre-merge blocks on a running Besu instance. It has the least downtime but may impact normal operations for lower spec users. Add the --history-expiry-prune option and restart your Besu node.

note

The early access option --Xpre-merge-pruning-quantity can be used to specify how many blocks to prune for each new block added to the chain. For example, --Xpre-merge-pruning-quantity=10. During testing on a 4 CPU machine, we only noticed an impact to Besu when this was tuned to 1000

The Besu logs will print the progress in the logs, and you'll see the Done pruning pre-merge blocks. message when complete.

Sync without pre-merge blocks​

This option has the most downtime but reclaims the most disk space. Delete your database and by default, syncing a Besu node using SNAP sync (--sync-mode=SNAP) will prune pre-merge blocks and only retain their headers.

If you're a solo staker, consider using RocketPool's rescue node to minimize downtime.