Add epochs since finalization check

Remove adhoc participation check
ethereum · Nov 28, 2022 · 64c7231 · 64c7231
1 parent 1c8cc82
commit 64c7231
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Showing 2 changed files with 22 additions and 28 deletions.
diff --git a/specs/bellatrix/fork-choice.md b/specs/bellatrix/fork-choice.md
@@ -108,26 +108,32 @@ def should_override_forkchoice_update(
     parent_root = head_block.parent_root
     parent_block = store.blocks[parent_root]
     current_slot = get_current_slot(store)
+    proposal_slot = head_block.slot + 1
 
     # Only re-org the head_block block if it arrived later than the attestation deadline.
     head_late = store.block_timeliness.get(head_root) is False
 
     # Only suppress the fork choice update if we are confident that we will propose the next block.
     parent_state_advanced = store.block_states[parent_root]
-    process_slots(parent_state_advanced, head_block.slot + 1)
+    process_slots(parent_state_advanced, proposal_slot)
     proposer_index = get_beacon_proposer_index(parent_state_advanced)
     proposing_reorg_slot = validator_is_connected(proposer_index)
 
+    # Do not re-org if the chain is not finalizing with acceptable frequency.
+    proposal_epoch = compute_epoch_at_slot(proposal_slot)
+    epochs_since_finalization = proposal_epoch - store.finalized_checkpoint.epoch
+    finalization_ok = epochs_since_finalization <= REORG_MAX_EPOCHS_SINCE_FINALIZATION
+
     # Single slot re-org.
     parent_slot_ok = parent_block.slot + 1 == head_block.slot
     time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
     current_time_ok = (head_block.slot == current_slot or
-                       (head_block.slot + 1 == current_slot and
+                       (proposal_slot == current_slot and
                         time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT))
     single_slot_reorg = parent_slot_ok and current_time_ok
 
     # Shuffling stable.
-    shuffling_stable = (head_block.slot + 1) % SLOTS_PER_EPOCH != 0
+    shuffling_stable = proposal_slot % SLOTS_PER_EPOCH != 0
 
     # FFG information of the new head_block will be competitive with the current head.
     # FIXME: needs more justification/finalization information in the store
@@ -138,14 +144,6 @@ def should_override_forkchoice_update(
     #        store.realized_finalization[head_root]
     ffg_competitive = True
 
-    # Ensure that total participation meets a minimum threshold.
-    # The participation multiplier is set to the number of slots for which the parent_block block has
-    # been known.
-    participation_multiplier = current_slot - parent_block.slot
-    parent_weight = get_latest_attesting_balance(store, parent_root)
-    participation_threshold = calculate_committee_fraction(justified_state, PARTICIPATION_THRESHOLD)
-    participation_ok = parent_weight >= participation_multiplier * participation_threshold
-
     # Check the head weight only if the attestations from the head slot have already been applied.
     # Implementations may want to do this in different ways, e.g. by advancing
     # `store.time` early, or by counting queued attestations during the head block's slot.
@@ -157,8 +155,8 @@ def should_override_forkchoice_update(
     else:
         head_weak = True
 
-    return all([head_late, proposing_reorg_slot, single_slot_reorg, shuffling_stable,
-                ffg_competitive, participation_ok, head_weak])
+    return all([head_late, proposing_reorg_slot, finalization_ok, single_slot_reorg,
+                shuffling_stable, ffg_competitive, head_weak])
 ```
 
 > Note that the ordering of conditions is a suggestion only. Implementations are free to

diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
@@ -76,13 +76,13 @@ Any of the above handlers that trigger an unhandled exception (e.g. a failed ass
 
 ### Configuration
 
-| Name                            | Value        |
-| ------------------------------- | ------------ |
-| `PROPOSER_SCORE_BOOST`          | `uint64(40)` |
-| `REORG_WEIGHT_THRESHOLD`        | `uint64(20)` |
-| `PARTICIPATION_THRESHOLD`       | `uint64(70)` |
+| Name                                  | Value        |
+| ------------------------------------- | ------------ |
+| `PROPOSER_SCORE_BOOST`                | `uint64(40)` |
+| `REORG_WEIGHT_THRESHOLD`              | `uint64(20)` |
+| `REORG_MAX_EPOCHS_SINCE_FINALIZATION` | `Epoch(2)`   |
 
-- The proposer score boost, re-org weight threshold and participation threshold are percentage
+- The proposer score boost and re-org weight threshold are percentage
   values that are measured with respect to the weight of a single committee. See
   `calculate_committee_fraction`.
 
@@ -301,6 +301,10 @@ def get_proposer_head(store: Store, head_root: Root, slot: Slot) -> Root:
     # Only re-org the head block if it arrived later than the attestation deadline.
     head_late = store.block_timeliness.get(head_root) is False
 
+    # Do not re-org if the chain is not finalizing with acceptable frequency.
+    epochs_since_finalization = compute_epoch_at_slot(slot) - store.finalized_checkpoint.epoch
+    finalization_ok = epochs_since_finalization <= REORG_MAX_EPOCHS_SINCE_FINALIZATION
+
     # Only re-org a single slot at most.
     single_slot_reorg = parent_block.slot + 1 == head_block.slot and head_block.slot + 1 == slot
 
@@ -316,21 +320,13 @@ def get_proposer_head(store: Store, head_root: Root, slot: Slot) -> Root:
     #        store.realized_finalization[head_root]
     ffg_competitive = True
 
-    # Ensure that total participation meets a minimum threshold. The factor of 2 accounts for votes
-    # from the head slot which should flow to the parent either via the head block or votes for
-    # emptiness.
-    participation_multiplier = 2
-    parent_weight = get_latest_attesting_balance(store, parent_root)
-    participation_threshold = calculate_committee_fraction(justified_state, PARTICIPATION_THRESHOLD)
-    participation_ok = parent_weight >= participation_multiplier * participation_threshold
-
     # Check that the head has few enough votes to be overpowered by our proposer boost.
     assert store.proposer_boost_root == Root()
     head_weight = get_latest_attesting_balance(store, head_root)
     reorg_threshold = calculate_committee_fraction(justified_state, REORG_WEIGHT_THRESHOLD)
     head_weak = head_weight < reorg_threshold
 
-    if all([head_late, single_slot_reorg, shuffling_stable, ffg_competitive, participation_ok,
+    if all([head_late, finalization_ok, single_slot_reorg, shuffling_stable, ffg_competitive,
             head_weak]):
         # We can re-org the current head by building upon its parent block.
         return parent_root