mirror of https://github.com/ethereum/go-ethereum
all: nuke total difficulty (#30744)
The total difficulty is the sum of all block difficulties from genesis to a certain block. This value was used in PoW for deciding which chain is heavier, and thus which chain to select. Since PoS has a different fork selection algorithm, all blocks since the merge have a difficulty of 0, and all total difficulties are the same for the past 2 years. Whilst the TDs are mostly useless nowadays, there was never really a reason to mess around removing them since they are so tiny. This reasoning changes when we go down the path of pruned chain history. In order to reconstruct any TD, we **must** retrieve all the headers from chain head to genesis and then iterate all the difficulties to compute the TD. In a world where we completely prune past chain segments (bodies, receipts, headers), it is not possible to reconstruct the TD at all. In a world where we still keep chain headers and prune only the rest, reconstructing it possible as long as we process (or download) the chain forward from genesis, but trying to snap sync the head first and backfill later hits the same issue, the TD becomes impossible to calculate until genesis is backfilled. All in all, the TD is a messy out-of-state, out-of-consensus computed field that is overall useless nowadays, but code relying on it forces the client into certain modes of operation and prevents other modes or other optimizations. This PR completely nukes out the TD from the node. It doesn't compute it, it doesn't operate on it, it's as if it didn't even exist. Caveats: - Whenever we have APIs that return TD (devp2p handshake, tracer, etc.) we return a TD of 0. - For era files, we recompute the TD during export time (fairly quick) to retain the format content. - It is not possible to "verify" the merge point (i.e. with TD gone, TTD is useless). Since we're not verifying PoW any more, just blindly trust it, not verifying but blindly trusting the many year old merge point seems just the same trust model. - Our tests still need to be able to generate pre and post merge blocks, so they need a new way to split the merge without TTD. The PR introduces a settable ttdBlock field on the consensus object which is used by tests as the block where originally the TTD happened. This is not needed for live nodes, we never want to generate old blocks. - One merge transition consensus test was disabled. With a non-operational TD, testing how the client reacts to TTD is useless, it cannot react. Questions: - Should we also drop total terminal difficulty from the genesis json? It's a number we cannot react on any more, so maybe it would be cleaner to get rid of even more concepts. --------- Co-authored-by: Gary Rong <garyrong0905@gmail.com>pull/31084/head
Péter Szilágyi
2 days ago
committed by
GitHub
parent
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// Copyright 2023 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package beacon |
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import ( |
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"math/big" |
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"github.com/ethereum/go-ethereum/consensus" |
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"github.com/ethereum/go-ethereum/core/types" |
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) |
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// NewFaker creates a fake consensus engine for testing.
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// The fake engine simulates a merged network.
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// It can not be used to test the merge transition.
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// This type is needed since the fakeChainReader can not be used with
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// a normal beacon consensus engine.
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func NewFaker() consensus.Engine { |
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return new(faker) |
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} |
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type faker struct { |
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Beacon |
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} |
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func (f *faker) CalcDifficulty(chain consensus.ChainHeaderReader, time uint64, parent *types.Header) *big.Int { |
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return beaconDifficulty |
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} |
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