web3.eth.getGasPrice sometimes returns 0 for xDai chain

[varasev]

• Parity Ethereum version: 1.11.8-stable, 2.0.8-stable
• Operating system: MacOS
• Installation: homebrew
• Fully synchronized: yes
• Network: xdai
• Restarted: yes

web3.eth.getGasPrice (web3 1.0 is used) sometimes returns 0 for xDai chain but sometimes it returns a correct value of 1 gwei.

However, for POA Sokol and POA Core it works fine: status-im/status-mobile#6388 (comment)

Seems something's wrong with eth_gasPrice JSON RPC for xDai chain which uses transactions with zero gas price for its bridge part.

I tried to launch Parity in the following manner:

parity --no-warp --jsonrpc-port 8545 --jsonrpc-apis all --chain ./spec.json --reserved-peers ./bootnodes.txt

spec.json and bootnodes.txt should be taken from here: https://github.com/poanetwork/poa-chain-spec/tree/dai

The code to reproduce:

const Web3 = require('web3');
const web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));

async function main() {
  setInterval(async function() {
    const res = await web3.eth.getGasPrice();
    console.log(res); // prints `1000000000` or `0`
  }, 5000);
}

main();

[jam10o-new]

@varasev just to make sure no recent fixes address this issue, can you try to replicate with a recent version of parity? (stable or beta?)

[varasev]

@joshua-mir The same is observed with 2.0.8-stable.

[varasev]

I've updated the description ☝️ to reproduce the bug on a local node.

[jam10o-new]

Thanks!

I have a hunch this has something to do with how we calculate the gas price to use based on previous blocks. I just checked out the block explorer for xDai and it looks like most blocks are empty, which might be the issue here.

@tomusdrw are you the right person to ask about this?

[tomusdrw]

@joshua-mir correct, gas price estimate is based on transactions from last blocks. If there is none we fallback to some default value, but if there are some transactions we will use their gas price.

Perhpas we should add a minimal bound to eth_gasPrice in case min-gas-price in CLI is set, cause afair the issue keeps returning.