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Opti sync: how to apply latestValidHash when payload is INVALID #2954

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Aug 3, 2022
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Opti sync: how to apply latestValidHash when payload is INVALID #2954

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4893f9e
Handling `latestValidHash` in opti-sync
mkalinin Jul 27, 2022
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Add ToC
hwwhww Jul 27, 2022
a60d0a5
Merge pull request #2956 from ethereum/opti-sync-toc
hwwhww Jul 28, 2022
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djrtwo Aug 1, 2022
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53 changes: 51 additions & 2 deletions sync/optimistic.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,37 @@
# Optimistic Sync

## Table of contents
<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->

- [Introduction](#introduction)
- [Constants](#constants)
- [Helpers](#helpers)
- [Mechanisms](#mechanisms)
- [When to optimistically import blocks](#when-to-optimistically-import-blocks)
- [How to optimistically import blocks](#how-to-optimistically-import-blocks)
- [How to apply `latestValidHash` when payload status is `INVALID`](#how-to-apply-latestvalidhash-when-payload-status-is-invalid)
- [Execution Engine Errors](#execution-engine-errors)
- [Assumptions about Execution Engine Behaviour](#assumptions-about-execution-engine-behaviour)
- [Re-Orgs](#re-orgs)
- [Fork Choice](#fork-choice)
- [Fork Choice Poisoning](#fork-choice-poisoning)
- [Checkpoint Sync (Weak Subjectivity Sync)](#checkpoint-sync-weak-subjectivity-sync)
- [Validator assignments](#validator-assignments)
- [Block Production](#block-production)
- [Attesting](#attesting)
- [Participating in Sync Committees](#participating-in-sync-committees)
- [Ethereum Beacon APIs](#ethereum-beacon-apis)
- [Design Decision Rationale](#design-decision-rationale)
- [Why `SAFE_SLOTS_TO_IMPORT_OPTIMISTICALLY`?](#why-safe_slots_to_import_optimistically)
- [Transitioning from VALID -> INVALIDATED or INVALIDATED -> VALID](#transitioning-from-valid---invalidated-or-invalidated---valid)
- [What about Light Clients?](#what-about-light-clients)
- [What if `TERMINAL_BLOCK_HASH` is used?](#what-if-terminal_block_hash-is-used)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->

## Introduction

In order to provide a syncing execution engine with a partial view of the head
Expand Down Expand Up @@ -163,6 +195,23 @@ the merge block MUST be treated the same as
an `INVALIDATED` block (i.e., it and all its descendants are invalidated and
removed from the block tree).

### How to apply `latestValidHash` when payload status is `INVALID`

Processing an `INVALID` payload status depends on the `latestValidHash` parameter.
The general approach is as follows:
1. Consensus engine MUST identify `invalidBlock` as per definition in the table below.
2. `invalidBlock` and all of its descendants MUST be transitioned from `NOT_VALIDATED` to `INVALIDATED`.

| `latestValidHash` | `invalidBlock` |
|:- |:- |
| Execution block hash | The *child* of a block with `body.execution_payload.block_hash == latestValidHash` in the chain containing the block with payload in question |
| `0x00..00` (all zeroes) | The first block with `body.execution_payload != ExecutionPayload()` in the chain containing a block with payload in question |
| `null` | Block with payload in question |

When `latestValidHash` is a meaningful execution block hash but consensus engine
cannot find a block satisfying `body.execution_payload.block_hash == latestValidHash`,
consensus engine SHOULD behave the same as if `latestValidHash` was `null`.

### Execution Engine Errors

When an execution engine returns an error or fails to respond to a payload
Expand Down Expand Up @@ -328,7 +377,7 @@ specification since it's only possible with a faulty EE.

Such a scenario requires manual intervention.

## What about Light Clients?
### What about Light Clients?

An alternative to optimistic sync is to run a light client inside/alongside
beacon nodes that mitigates the need for optimistic sync by providing
Expand All @@ -340,7 +389,7 @@ A notable thing about optimistic sync is that it's *optional*. Should an
implementation decide to go the light-client route, then they can just ignore
optimistic sync all together.

## What if `TERMINAL_BLOCK_HASH` is used?
### What if `TERMINAL_BLOCK_HASH` is used?

If the terminal block hash override is used (i.e., `TERMINAL_BLOCK_HASH !=
Hash32()`), the [`validate_merge_block`](../specs/bellatrix/fork-choice.md#validate_merge_block)
Expand Down