Set default --tx-pool-price-bump to 0 for zeroBaseFee chains

[matthew1001]

Description

See discord discussion https://discord.com/channels/905194001349627914/905205502940696607/1163795216256471042

After discussion with @fab-10 and @ajsutton there was a general consensus that for free gas chains, the price bump % ought to be set to a default value of 0%, instead of 10%. Replacement of transactions in a free gas chain where priceBump != 0 is effectively impossible and relies on unpleasant work-arounds (such as setting TX pool retention to 1 hour and waiting for it to be removed).

Acceptance Criteria

When I create a new Besu node with zeroBaseFee=0 and/or --max-gas-price=0 the value of --tx-pool-price-bump is set to a default value of 0. I can change it back to 10% or any other valid value by setting it manually.

[matthew1001]

Having raised this, I re-tested the effect of --tx-pool-price-bump=0 with non-EIP1559 transactions, and even setting it to 0 does not allow you to replace a transaction.

It would require the addition of e.g.

if (priceBump.getValue() == 0
        && existingPendingTransaction.getGasPrice().compareTo(newPendingTransaction.getGasPrice())
            == 0) {
      return true;
}

to TransactionReplacementByGasPriceRule.shouldReplace() for it to accept a new transaction as the replacement for an old one with the same gasPrice.

I would have added the above under this or another issue, but my concern is that the EIP1559 test (TransactionReplacementByFeeMarketRule.shouldReplace()) has a specific check for the new TX having 0:

// bail early if price is not strictly positive
    if (newEffPrice.equals(Wei.ZERO)) {
      return false;
}

So I'm reticent to put a change like ^^ in since anyone who switched from gasPrice to maxBaseFee/maxPriorityFee would suddenly see a breaking change in TX replacement behaviour.

[fab-10]

I think, that we just miss the specific transaction replacement rule for zero base fee chains, like we have it for the other fee market. Such rule can just accept any replacement without checking the price.

[fab-10]

@matthew1001 Following you initial investigation, I have made this PR #6079 that should make --tx-pool-price-bump=0 works as expected, could you give it a try?

[matthew1001]

Thanks @fab-10 Sorry for the delay, just back from a week off. Yes I'd be happy to give it a try, I'll pull the branch now.