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nimbus-eth2/beacon_chain/consensus_object_pools/block_quarantine.nim

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# beacon_chain
# Copyright (c) 2018-2022 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
{.push raises: [Defect].}
import
std/[tables],
stew/bitops2,
../spec/forks
export tables, forks
const
MaxMissingItems = 1024
## Arbitrary
MaxOrphans = SLOTS_PER_EPOCH * 3
## Enough for finalization in an alternative fork
MaxUnviables = 16 * 1024
## About a day of blocks - most likely not needed but it's quite cheap..
type
MissingBlock* = object
tries*: int
FetchRecord* = object
root*: Eth2Digest
Quarantine* = object
## Keeps track of unvalidated blocks coming from the network
## and that cannot yet be added to the chain
##
## This only stores blocks that cannot be linked to the
## ChainDAGRef DAG due to missing ancestor(s).
##
## Trivially invalid blocks may be dropped before reaching this stage.
orphans*: Table[(Eth2Digest, ValidatorSig), ForkedSignedBeaconBlock]
## Blocks that we don't have a parent for - when we resolve the parent, we
## can proceed to resolving the block as well - we index this by root and
## signature such that a block with invalid signature won't cause a block
## with a valid signature to be dropped
unviable*: OrderedTable[Eth2Digest, tuple[]]
## Unviable blocks are those that come from a history that does not
## include the finalized checkpoint we're currently following, and can
## therefore never be included in our canonical chain - we keep their hash
## around so that we can avoid cluttering the orphans table with their
## descendants - the ChainDAG only keeps track blocks that make up the
## valid and canonical history.
##
## Entries are evicted in FIFO order - recent entries are more likely to
## appear again in attestations and blocks - however, the unviable block
## table is not a complete directory of all unviable blocks circulating -
## only those we have observed, been able to verify as unviable and fit
## in this cache.
missing*: Table[Eth2Digest, MissingBlock]
## Roots of blocks that we would like to have (either parent_root of
## unresolved blocks or block roots of attestations)
func init*(T: type Quarantine): T =
T()
func checkMissing*(quarantine: var Quarantine): seq[FetchRecord] =
## Return a list of blocks that we should try to resolve from other client -
## to be called periodically but not too often (once per slot?)
var done: seq[Eth2Digest]
for k, v in quarantine.missing.mpairs():
if v.tries > 8:
done.add(k)
else:
inc v.tries
for k in done:
quarantine.missing.del(k)
# simple (simplistic?) exponential backoff for retries..
for k, v in quarantine.missing.pairs():
if countOnes(v.tries.uint64) == 1:
result.add(FetchRecord(root: k))
# TODO stew/sequtils2
template anyIt(s, pred: untyped): bool =
# https://github.com/nim-lang/Nim/blob/version-1-2/lib/pure/collections/sequtils.nim#L682-L704
# without the items(...)
var result = false
for it {.inject.} in s:
if pred:
result = true
break
result
func addMissing*(quarantine: var Quarantine, root: Eth2Digest) =
## Schedule the download a the given block
if quarantine.missing.len >= MaxMissingItems:
return
if root in quarantine.unviable:
# Won't get anywhere with this block
return
# It's not really missing if we're keeping it in the quarantine
if anyIt(quarantine.orphans.keys, it[0] == root):
return
# Add if it's not there, but don't update missing counter
discard quarantine.missing.hasKeyOrPut(root, MissingBlock())
func removeOrphan*(
quarantine: var Quarantine, signedBlock: ForkySignedBeaconBlock) =
quarantine.orphans.del((signedBlock.root, signedBlock.signature))
func isViableOrphan(
finalizedSlot: Slot, signedBlock: ForkedSignedBeaconBlock): bool =
# The orphan must be newer than the finalization point so that its parent
# either is the finalized block or more recent
let
slot = getForkedBlockField(signedBlock, slot)
slot > finalizedSlot
func cleanupUnviable(quarantine: var Quarantine) =
while quarantine.unviable.len() >= MaxUnviables:
var toDel: Eth2Digest
for k in quarantine.unviable.keys():
toDel = k
break # Cannot modify while for-looping
quarantine.unviable.del(toDel)
func addUnviable*(quarantine: var Quarantine, root: Eth2Digest) =
if root in quarantine.unviable:
return
quarantine.cleanupUnviable()
# Remove the tree of orphans whose ancestor is unviable - they are now also
# unviable! This helps avoiding junk in the quarantine, because we don't keep
# unviable parents in the DAG and there's no way to tell an orphan from an
# unviable block without the parent.
var
toRemove: seq[(Eth2Digest, ValidatorSig)] # Can't modify while iterating
toCheck = @[root]
while toCheck.len > 0:
let root = toCheck.pop()
for k, v in quarantine.orphans.mpairs():
if getForkedBlockField(v, parent_root) == root:
toCheck.add(k[0])
toRemove.add(k)
elif k[0] == root:
toRemove.add(k)
for k in toRemove:
quarantine.orphans.del k
quarantine.unviable.add(k[0], ())
toRemove.setLen(0)
quarantine.unviable.add(root, ())
func cleanupOrphans(quarantine: var Quarantine, finalizedSlot: Slot) =
var toDel: seq[(Eth2Digest, ValidatorSig)]
for k, v in quarantine.orphans.pairs():
if not isViableOrphan(finalizedSlot, v):
toDel.add k
for k in toDel:
quarantine.addUnviable k[0]
func clearAfterReorg*(quarantine: var Quarantine) =
## Clear missing and orphans to start with a fresh slate in case of a reorg
## Unviables remain unviable and are not cleared.
quarantine.missing.reset()
quarantine.orphans.reset()
# Typically, blocks will arrive in mostly topological order, with some
# out-of-order block pairs. Therefore, it is unhelpful to use either a
# FIFO or LIFO discpline, and since by definition each block gets used
# either 0 or 1 times it's not a cache either. Instead, stop accepting
# new blocks, and rely on syncing to cache up again if necessary.
#
# For typical use cases, this need not be large, as they're two or three
# blocks arriving out of order due to variable network delays. As blocks
# for future slots are rejected before reaching quarantine, this usually
# will be a block for the last couple of slots for which the parent is a
# likely imminent arrival.
func addOrphan*(
quarantine: var Quarantine, finalizedSlot: Slot,
signedBlock: ForkedSignedBeaconBlock): bool =
## Adds block to quarantine's `orphans` and `missing` lists.
if not isViableOrphan(finalizedSlot, signedBlock):
quarantine.addUnviable(signedBlock.root)
return false
quarantine.cleanupOrphans(finalizedSlot)
let parent_root = getForkedBlockField(signedBlock, parent_root)
if parent_root in quarantine.unviable:
quarantine.unviable.add(signedBlock.root, ())
return true
# Even if the quarantine is full, we need to schedule its parent for
# downloading or we'll never get to the bottom of things
quarantine.addMissing(parent_root)
if quarantine.orphans.lenu64 >= MaxOrphans:
return false
quarantine.orphans[(signedBlock.root, signedBlock.signature)] =
signedBlock
quarantine.missing.del(signedBlock.root)
true
iterator pop*(quarantine: var Quarantine, root: Eth2Digest):
ForkedSignedBeaconBlock =
# Pop orphans whose parent is the block identified by `root`
var toRemove: seq[(Eth2Digest, ValidatorSig)]
defer: # Run even if iterator is not carried to termination
for k in toRemove:
quarantine.orphans.del k
for k, v in quarantine.orphans.mpairs():
if getForkedBlockField(v, parent_root) == root:
toRemove.add(k)
yield v
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