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feat(sync): use an explicit peer for backfilling

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Youngjoon Lee 2025-04-10 17:33:24 +09:00
parent 2c5c3860f0
commit 7afed1952c
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GPG Key ID: D94003D91DE12141
1 changed files with 37 additions and 37 deletions
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74
cryptarchia/sync.py
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@ -1,3 +1,5 @@
from __future__ import annotations
from collections import defaultdict
from typing import Generator
@ -23,7 +25,7 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
# If the backfilling fails, it means that the checkpoint chain is invalid,
# and the sync process should be cancelled.
if checkpoint:
backfill_fork(local, checkpoint.block, block_fetcher)
backfill_fork(local, checkpoint.block, None, block_fetcher)
# Repeat the sync process until no peer has a tip ahead of the local tip,
# because peers' tips may advance during the sync process.
@ -33,9 +35,9 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
# Gather orphaned blocks, which are blocks from forks that are absent in the local block tree.
start_slot = local.tip().slot
orphans: set[BlockHeader] = set()
orphans: dict[BlockHeader, BlockFetcher.PeerId] = dict()
num_blocks = 0
for block in block_fetcher.fetch_blocks_from(start_slot):
for block, peer_id in block_fetcher.fetch_blocks_from(start_slot):
num_blocks += 1
# Reject blocks that have been rejected in the past
# or whose parent has been rejected.
@ -45,9 +47,9 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
try:
local.on_block(block)
orphans.discard(block)
orphans.pop(block, None)
except ParentNotFound:
orphans.add(block)
orphans[block] = peer_id
except Exception:
rejected_blocks.add(block.id())
@ -59,7 +61,7 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
# Backfill the orphan forks starting from the orphan blocks with applying fork choice rule.
#
# Sort the orphan blocks by slot in descending order to minimize the number of backfillings.
for orphan in sorted(orphans, key=lambda b: b.slot, reverse=True):
for orphan, peer_id in sorted(orphans.items(), key=lambda item: item[0].slot, reverse=True):
# Skip the orphan block if it has been processed during the previous backfillings
# (i.e. if it has been already added to the local block tree).
# Or, skip if it has been rejected during the previous backfillings.
@ -68,7 +70,7 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
and orphan.id() not in rejected_blocks
):
try:
backfill_fork(local, orphan, block_fetcher)
backfill_fork(local, orphan, peer_id, block_fetcher)
except InvalidBlockFromBackfillFork as e:
rejected_blocks.update(block.id() for block in e.invalid_suffix)
@ -76,14 +78,15 @@ def sync(local: Follower, peers: list[Follower], checkpoint: LedgerState | None
def backfill_fork(
local: Follower,
fork_tip: BlockHeader,
block_fetcher: "BlockFetcher",
fork_peer_id: BlockFetcher.PeerId | None,
block_fetcher: BlockFetcher,
):
# Backfills a fork, which is absent in the local block tree, by fetching blocks from the peers.
# During backfilling, the fork choice rule is continuously applied.
suffix = find_missing_part(
local,
block_fetcher.fetch_chain_backward(fork_tip.id(), local),
block_fetcher.fetch_chain_backward(fork_tip.id(), fork_peer_id),
)
# Add blocks in the fork suffix with applying fork choice rule.
@ -116,39 +119,43 @@ class BlockFetcher:
# NOTE: This class is a mock, which uses a naive approach to fetch blocks from multiple peers.
# In real implementation, any optimized way can be used, such as parallel fetching.
def __init__(self, peers: list[Follower]):
self.peers = peers
PeerId = int
def fetch_blocks_from(self, start_slot: Slot) -> Generator[BlockHeader, None, None]:
def __init__(self, peers: list[Follower]):
self.peers = dict()
for peer_id, peer in enumerate(peers):
self.peers[peer_id] = peer
def fetch_blocks_from(self, start_slot: Slot) -> Generator[tuple[BlockHeader, PeerId], None, None]:
# Filter peers that have a tip ahead of the local tip
# and group peers by their tip to minimize the number of fetches.
groups = self.filter_and_group_peers_by_tip(start_slot)
for group in groups.values():
for block in BlockFetcher.fetch_blocks_by_slot(group, start_slot):
yield block
for block, peer_id in BlockFetcher.fetch_blocks_by_slot(group, start_slot):
yield block, peer_id
def filter_and_group_peers_by_tip(
self, start_slot: Slot
) -> dict[BlockHeader, list[Follower]]:
) -> dict[BlockHeader, dict[PeerId, Follower]]:
# Group peers by their tip.
# Filter only the peers whose tip is ahead of the start_slot.
groups: dict[BlockHeader, list[Follower]] = defaultdict(list)
for peer in self.peers:
groups = defaultdict(dict)
for peer_id, peer in self.peers.items():
if peer.tip().slot.absolute_slot > start_slot.absolute_slot:
groups[peer.tip()].append(peer)
groups[peer.tip()][peer_id] = peer
return groups
@staticmethod
def fetch_blocks_by_slot(
peers: list[Follower], start_slot: Slot
) -> Generator[BlockHeader, None, None]:
peers: dict[PeerId, Follower], start_slot: Slot
) -> Generator[tuple[BlockHeader, PeerId], None, None]:
# Fetch blocks in the given range of slots from one of the peers.
# Blocks should be returned in order of slot.
# If a peer fails, try the next peer.
for peer in peers:
for peer_id, peer in peers.items():
try:
for block in peer.blocks_by_slot(start_slot):
yield block
yield block, peer_id
# Update start_slot for the potential try with the next peer.
start_slot = block.slot
# The peer successfully returned all blocks. No need to try the next peer.
@ -157,25 +164,18 @@ class BlockFetcher:
continue
def fetch_chain_backward(
self, tip: Hash, local: Follower
self, tip: Hash, peer_id: PeerId | None,
) -> Generator[BlockHeader, None, None]:
# Fetches a chain of blocks from the peers, starting from the given tip to the genesis.
# Attempts to extend the chain as much as possible by querying multiple peers,
# considering that not all peers may have the full chain (from the genesis).
# Fetches a chain of blocks from a peer, starting from the given tip to the genesis.
# If peer_id is not set, fetch the chain by querying multiple peers.
id = tip
# First, try to iterate the chain from the local block tree.
for block in iter_chain_blocks(id, local.ledger_state):
yield block
if block.id() == local.genesis_state.block.id():
return
id = block.parent
# Try to continue by fetching the remaining blocks from the peers
for peer in self.peers:
peers = [self.peers[peer_id]] if peer_id is not None else list(self.peers.values())
for peer in peers:
for block in iter_chain_blocks(id, peer.ledger_state):
yield block
if block.id() == local.genesis_state.block.id():
if block.id() == peer.genesis_state.block.id():
# Received the entire chain from the peer.
# No need to continue with the next peer.
return
id = block.parent