PulseVM

A virtual machine built for Metal Blockchain based on the XPR Network protocol, aka EOS / Leap / Spring.

Notable changes

Objective CPU calculation

EOS calculates CPU subjectively by charging the actual time it took a producer to execute a certain transaction. This is far from ideal as producers on slower hardware would charge more CPU than producers with faster hardware.

PulseVM calculates CPU objectively by charging a baseline of 50 microseconds per action. In addition, WebAssembly modules are instrumented with an instruction counter which allows it to calculate the exact amount of instructions a certain action performed.

Instant finality

PulseVM blocks have near instant finality, improving on the average of 120 seconds seen in XPR Network.

It does this by handling a mempool of transactions, every 500 milliseconds the mempool is checked for transactions.

If the mempool contains transactions then the producer will request metalgo to produce a block, the actual producer building the block might be different from the producer requesting it. This is determined by the production window metalgo enforces.

The producer that built the block will then submit the block to other producer for verification. If consensus is reached then all producers will be asked to accept the block.

This process takes around 200 milliseconds depending on various factors.

Requirements

• Supported OS
  • Ubuntu 22.04 or greater
  • Mac OSX
• zstd
  • For Mac: brew install zstd
• LLVM >= 18: used to compile and run WebAssembly contracts
  • For Mac: brew install llvm@18

If you are getting a zstd error on Mac, try:

export LIBRARY_PATH="$(brew --prefix zstd)/lib:${LIBRARY_PATH:-}"
export CPATH="$(brew --prefix zstd)/include:${CPATH:-}"

Run locally

Spin up a local cluster using metal-network-runner

metal-network-runner server \
--log-level info \
--port=":8080" \
--grpc-gateway-port=":8081"

Start a clean instance of the virtual machine

Make sure METALGO_EXEC_PATH points to a compiled metalgo binary. The --plugin-dir directive should point to a directory that has a compiled version of this virtual machine, the binary should be renamed to rXcAFxZvio99epp6TzEwYfexCfPAbJuBTMsjUUoiT7PkVykNs as that is what metalgo will be looking for.

metal-network-runner control start --log-level info \
--endpoint="0.0.0.0:8080" \
--number-of-nodes=5 \
--metalgo-path ${METALGO_EXEC_PATH} \
--plugin-dir $(pwd)/build \
--blockchain-specs '[{"vm_name": "pulsevm", "genesis": "/Users/glennmarien/Documents/MetalBlockchain/pulsevm/genesis.json"}]'