122 lines
5.4 KiB
Markdown
122 lines
5.4 KiB
Markdown
# Ethereum 2.0 The Merge
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**Notice**: This document is a work-in-progress for researchers and implementers.
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## Table of contents
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Introduction](#introduction)
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- [Configuration](#configuration)
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- [Fork to Merge](#fork-to-merge)
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- [Fork trigger](#fork-trigger)
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- [Upgrading the state](#upgrading-the-state)
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- [Initializing transition store](#initializing-transition-store)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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## Introduction
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This document describes the process of the Merge upgrade.
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## Configuration
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Warning: this configuration is not definitive.
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| Name | Value |
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| - | - |
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| `MERGE_FORK_VERSION` | `Version('0x02000000')` |
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| `MERGE_FORK_EPOCH` | `Epoch(18446744073709551615)` **TBD** |
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| `MIN_ANCHOR_POW_BLOCK_DIFFICULTY` | **TBD** |
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| `TARGET_SECONDS_TO_MERGE` | `uint64(7 * 86400)` = (604,800) |
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## Fork to Merge
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### Fork trigger
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TBD. Social consensus, along with state conditions such as epoch boundary, finality, deposits, active validator count, etc. may be part of the decision process to trigger the fork. For now we assume the condition will be triggered at epoch `MERGE_FORK_EPOCH`.
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Since the Merge transition process relies on `Eth1Data` in the beacon state we do want to make sure that this data is fresh. This is achieved by forcing `MERGE_FORK_EPOCH` to point to eth1 voting period boundary, i.e. `MERGE_FORK_EPOCH` should satisfy the following condition `MERGE_FORK_EPOCH % EPOCHS_PER_ETH1_VOTING_PERIOD == 0`.
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Note that for the pure Merge networks, we don't apply `upgrade_to_merge` since it starts with Merge version logic.
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### Upgrading the state
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If `state.slot % SLOTS_PER_EPOCH == 0` and `compute_epoch_at_slot(state.slot) == MERGE_FORK_EPOCH`, an irregular state change is made to upgrade to Merge.
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The upgrade occurs after the completion of the inner loop of `process_slots` that sets `state.slot` equal to `MERGE_FORK_EPOCH * SLOTS_PER_EPOCH`.
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Care must be taken when transitioning through the fork boundary as implementations will need a modified [state transition function](../phase0/beacon-chain.md#beacon-chain-state-transition-function) that deviates from the Phase 0 document.
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In particular, the outer `state_transition` function defined in the Phase 0 document will not expose the precise fork slot to execute the upgrade in the presence of skipped slots at the fork boundary. Instead the logic must be within `process_slots`.
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```python
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def upgrade_to_merge(pre: phase0.BeaconState) -> BeaconState:
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epoch = phase0.get_current_epoch(pre)
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post = BeaconState(
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# Versioning
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genesis_time=pre.genesis_time,
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genesis_validators_root=pre.genesis_validators_root,
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slot=pre.slot,
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fork=Fork(
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previous_version=pre.fork.current_version,
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current_version=MERGE_FORK_VERSION,
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epoch=epoch,
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),
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# History
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latest_block_header=pre.latest_block_header,
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block_roots=pre.block_roots,
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state_roots=pre.state_roots,
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historical_roots=pre.historical_roots,
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# Eth1
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eth1_data=pre.eth1_data,
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eth1_data_votes=pre.eth1_data_votes,
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eth1_deposit_index=pre.eth1_deposit_index,
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# Registry
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validators=pre.validators,
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balances=pre.balances,
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# Randomness
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randao_mixes=pre.randao_mixes,
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# Slashings
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slashings=pre.slashings,
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# Attestations
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previous_epoch_attestations=pre.previous_epoch_attestations,
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current_epoch_attestations=pre.current_epoch_attestations,
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# Finality
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justification_bits=pre.justification_bits,
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previous_justified_checkpoint=pre.previous_justified_checkpoint,
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current_justified_checkpoint=pre.current_justified_checkpoint,
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finalized_checkpoint=pre.finalized_checkpoint,
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# Execution-layer
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latest_execution_payload_header=ExecutionPayloadHeader(),
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)
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return post
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```
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### Initializing transition store
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If `state.slot % SLOTS_PER_EPOCH == 0` and `compute_epoch_at_slot(state.slot) == MERGE_FORK_EPOCH`, a transition store is initialized to be further utilized by the transition process of the Merge.
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Transition store initialization occurs after the state has been modified by corresponding `upgrade_to_merge` function.
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```python
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def compute_transition_total_difficulty(anchor_pow_block: PowBlock) -> uint256:
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seconds_per_voting_period = EPOCHS_PER_ETH1_VOTING_PERIOD * SLOTS_PER_EPOCH * SECONDS_PER_SLOT
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pow_blocks_per_voting_period = seconds_per_voting_period // SECONDS_PER_ETH1_BLOCK
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pow_blocks_to_merge = TARGET_SECONDS_TO_MERGE // SECONDS_PER_ETH1_BLOCK
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pow_blocks_after_anchor_block = ETH1_FOLLOW_DISTANCE + pow_blocks_per_voting_period + pow_blocks_to_merge
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anchor_difficulty = max(MIN_ANCHOR_POW_BLOCK_DIFFICULTY, anchor_pow_block.difficulty)
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return anchor_pow_block.total_difficulty + anchor_difficulty * pow_blocks_after_anchor_block
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def get_transition_store(anchor_pow_block: PowBlock) -> TransitionStore:
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transition_total_difficulty = compute_transition_total_difficulty(anchor_pow_block)
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return TransitionStore(transition_total_difficulty=transition_total_difficulty)
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def initialize_transition_store(state: BeaconState) -> TransitionStore:
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pow_block = get_pow_block(state.eth1_data.block_hash)
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return get_transition_store(pow_block)
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```
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