How to run Bitcoin Core 31.1-lean with relay block size policy.
Bitcoin Lean is a fork of Bitcoin Core v31.1 with two relay policy changes:
Lean Blocks (-relayblocksize): Blocks exceeding the configured total size limit are validated and stored but not relayed or served to peers.
Lean Data (-datacarriersize): MAX_OP_RETURN_RELAY is set to 83 bytes (the pre-v30.0 default) instead of 100,000 bytes.
The node validates all blocks against all consensus rules. It stores all blocks on disk. It does not propagate blocks that exceed the size limit.
Build from source:
git clone https://gitworkshop.dev/npub1c9gyxxxf2l2g26ga0menv2lueh870w744s729u0cp3pm5y3fkv3sw4wghc/relay.ngit.dev/Bitcoin-Core-.git
cd Bitcoin-Core-
git checkout lean/v31.1
cmake -B build
cmake --build build -j$(sysctl -n hw.ncpu)
Run with lean policy:
bitcoind -relayblocksize=1600000 -datacarriersize=83
Or in bitcoin.conf:
relayblocksize=1600000
datacarriersize=83
-relayblocksize accepts an integer in bytes. 1,600,000 = 1.6MB. Set to 0 or omit to disable.
When the node receives a block:
1. Block is validated against all consensus rules. If invalid, it is rejected.
2. Block is stored on disk. Full data including witness.
3. If total size (L0 + L1) exceeds -relayblocksize:
the block is not announced to peers and not served on getdata requests.
Peers that need the block fetch it from a node that does not enforce the limit.
1,600,000 (1.6MB) → 35% of recent blocks comply
1,400,000 (1.4MB) → 11% comply
1,200,000 (1.2MB) → ~5% comply
1,000,000 (1.0MB) → ~2% comply
Lower limits filter more blocks. The limit can be changed by restarting bitcoind with a different value.
Log entries when blocks are filtered:
relayblocksize: skipping announcement for oversized block <hash>
relayblocksize: not serving oversized block <hash> to peer=<id>
Bitcoin Lean nodes validate the same consensus rules as standard Bitcoin Core nodes. They store the same chain data. They participate in the same network.
The only difference: lean nodes do not relay or serve blocks that exceed the configured size limit. Standard nodes relay all blocks.
Both types of nodes can run on the same network. Lean nodes and standard nodes connect to each other normally.
When a node enforces a total block size limit at the relay layer:
Propagation: Blocks exceeding the limit propagate through fewer nodes. Blocks within the limit propagate through all nodes.
Fees: Transactions in blocks that exceed the limit reach fewer nodes before the next block is mined. Transactions in compliant blocks reach all nodes.
Block templates: Miners who want their blocks relayed by lean nodes must fit within the limit. Miners who do not care about lean relay can produce larger blocks.
Adoption: The more nodes that enforce the limit, the more blocks must comply to propagate fully.