eth: use the last announced finalized block as the sync ancient limit

eth/catalyst/api.go

@@ -237,15 +237,27 @@ func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payl
 			log.Warn("Forkchoice requested unknown head", "hash", update.HeadBlockHash)
 			return engine.STATUS_SYNCING, nil
 		}
+		// If the finalized hash is known, we can direct the downloader to move
+		// potentially more data to the freezer from the get go.
+		finalized := api.remoteBlocks.get(update.FinalizedBlockHash)
+
 		// Header advertised via a past newPayload request. Start syncing to it.
 		// Before we do however, make sure any legacy sync in switched off so we
 		// don't accidentally have 2 cycles running.
 		if merger := api.eth.Merger(); !merger.TDDReached() {
 			merger.ReachTTD()
 			api.eth.Downloader().Cancel()
 		}
-		log.Info("Forkchoice requested sync to new head", "number", header.Number, "hash", header.Hash())
-		if err := api.eth.Downloader().BeaconSync(api.eth.SyncMode(), header); err != nil {
+		context := []interface{}{"number", header.Number, "hash", header.Hash()}
+		if update.FinalizedBlockHash != (common.Hash{}) {
+			if finalized == nil {
+				context = append(context, []interface{}{"finalized", "unknown"}...)
+			} else {
+				context = append(context, []interface{}{"finalized", finalized.Number}...)
+			}
+		}
+		log.Info("Forkchoice requested sync to new head", context...)
+		if err := api.eth.Downloader().BeaconSync(api.eth.SyncMode(), header, finalized); err != nil {
 			return engine.STATUS_SYNCING, err
 		}
 		return engine.STATUS_SYNCING, nil

eth/catalyst/queue.go

@@ -31,9 +31,12 @@ import (
 const maxTrackedPayloads = 10
 
 // maxTrackedHeaders is the maximum number of executed payloads the execution
-// engine tracks before evicting old ones. Ideally we should only ever track the
-// latest one; but have a slight wiggle room for non-ideal conditions.
-const maxTrackedHeaders = 10
+// engine tracks before evicting old ones. These are tracked outside the chain
+// during initial sync to allow ForkchoiceUpdate to reference past blocks via
+// hashes only. For the sync target it would be enough to track only the latest
+// header, but snap sync also needs the latest finalized height for the ancient
+// limit.
+const maxTrackedHeaders = 96
 
 // payloadQueueItem represents an id->payload tuple to store until it's retrieved
 // or evicted.

eth/catalyst/tester.go

@@ -75,7 +75,7 @@ func (tester *FullSyncTester) Start() error {
 				}
 				// Trigger beacon sync with the provided block header as
 				// trusted chain head.
-				err := tester.api.eth.Downloader().BeaconSync(downloader.FullSync, tester.block.Header())
+				err := tester.api.eth.Downloader().BeaconSync(downloader.FullSync, tester.block.Header(), nil)
 				if err != nil {
 					log.Info("Failed to beacon sync", "err", err)
 				}

eth/downloader/beaconsync.go

@@ -151,8 +151,8 @@ func (d *Downloader) SetBadBlockCallback(onBadBlock badBlockFn) {
 //
 // Internally backfilling and state sync is done the same way, but the header
 // retrieval and scheduling is replaced.
-func (d *Downloader) BeaconSync(mode SyncMode, head *types.Header) error {
-	return d.beaconSync(mode, head, true)
+func (d *Downloader) BeaconSync(mode SyncMode, head *types.Header, final *types.Header) error {
+	return d.beaconSync(mode, head, final, true)
 }
 
 // BeaconExtend is an optimistic version of BeaconSync, where an attempt is made
@@ -162,7 +162,7 @@ func (d *Downloader) BeaconSync(mode SyncMode, head *types.Header) error {
 // This is useful if a beacon client is feeding us large chunks of payloads to run,
 // but is not setting the head after each.
 func (d *Downloader) BeaconExtend(mode SyncMode, head *types.Header) error {
-	return d.beaconSync(mode, head, false)
+	return d.beaconSync(mode, head, nil, false)
 }
 
 // beaconSync is the post-merge version of the chain synchronization, where the
@@ -171,7 +171,7 @@ func (d *Downloader) BeaconExtend(mode SyncMode, head *types.Header) error {
 //
 // Internally backfilling and state sync is done the same way, but the header
 // retrieval and scheduling is replaced.
-func (d *Downloader) beaconSync(mode SyncMode, head *types.Header, force bool) error {
+func (d *Downloader) beaconSync(mode SyncMode, head *types.Header, final *types.Header, force bool) error {
 	// When the downloader starts a sync cycle, it needs to be aware of the sync
 	// mode to use (full, snap). To keep the skeleton chain oblivious, inject the
 	// mode into the backfiller directly.
@@ -181,7 +181,7 @@ func (d *Downloader) beaconSync(mode SyncMode, head *types.Header, force bool) e
 	d.skeleton.filler.(*beaconBackfiller).setMode(mode)
 
 	// Signal the skeleton sync to switch to a new head, however it wants
-	if err := d.skeleton.Sync(head, force); err != nil {
+	if err := d.skeleton.Sync(head, final, force); err != nil {
 		return err
 	}
 	return nil
@@ -207,7 +207,7 @@ func (d *Downloader) findBeaconAncestor() (uint64, error) {
 	number := chainHead.Number.Uint64()
 
 	// Retrieve the skeleton bounds and ensure they are linked to the local chain
-	beaconHead, beaconTail, err := d.skeleton.Bounds()
+	beaconHead, beaconTail, _, err := d.skeleton.Bounds()
 	if err != nil {
 		// This is a programming error. The chain backfiller was called with an
 		// invalid beacon sync state. Ideally we would panic here, but erroring
@@ -272,7 +272,7 @@ func (d *Downloader) findBeaconAncestor() (uint64, error) {
 // until sync errors or is finished.
 func (d *Downloader) fetchBeaconHeaders(from uint64) error {
 	var head *types.Header
-	_, tail, err := d.skeleton.Bounds()
+	_, tail, _, err := d.skeleton.Bounds()
 	if err != nil {
 		return err
 	}
@@ -292,7 +292,7 @@ func (d *Downloader) fetchBeaconHeaders(from uint64) error {
 	for {
 		// Some beacon headers might have appeared since the last cycle, make
 		// sure we're always syncing to all available ones
-		head, _, err = d.skeleton.Bounds()
+		head, _, _, err = d.skeleton.Bounds()
 		if err != nil {
 			return err
 		}

eth/downloader/downloader.go

@@ -480,7 +480,7 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td, ttd *
 	}(time.Now())
 
 	// Look up the sync boundaries: the common ancestor and the target block
-	var latest, pivot *types.Header
+	var latest, pivot, final *types.Header
 	if !beaconMode {
 		// In legacy mode, use the master peer to retrieve the headers from
 		latest, pivot, err = d.fetchHead(p)
@@ -489,7 +489,7 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td, ttd *
 		}
 	} else {
 		// In beacon mode, use the skeleton chain to retrieve the headers from
-		latest, _, err = d.skeleton.Bounds()
+		latest, _, final, err = d.skeleton.Bounds()
 		if err != nil {
 			return err
 		}
@@ -499,7 +499,7 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td, ttd *
 			// Retrieve the pivot header from the skeleton chain segment but
 			// fallback to local chain if it's not found in skeleton space.
 			if pivot = d.skeleton.Header(number); pivot == nil {
-				_, oldest, _ := d.skeleton.Bounds() // error is already checked
+				_, oldest, _, _ := d.skeleton.Bounds() // error is already checked
 				if number < oldest.Number.Uint64() {
 					count := int(oldest.Number.Uint64() - number) // it's capped by fsMinFullBlocks
 					headers := d.readHeaderRange(oldest, count)
@@ -567,26 +567,41 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td, ttd *
 		d.committed = 0
 	}
 	if mode == SnapSync {
-		// Set the ancient data limitation.
-		// If we are running snap sync, all block data older than ancientLimit will be
-		// written to the ancient store. More recent data will be written to the active
-		// database and will wait for the freezer to migrate.
+		// Set the ancient data limitation. If we are running snap sync, all block
+		// data older than ancientLimit will be written to the ancient store. More
+		// recent data will be written to the active database and will wait for the
+		// freezer to migrate.
 		//
-		// If there is a checkpoint available, then calculate the ancientLimit through
-		// that. Otherwise calculate the ancient limit through the advertised height
-		// of the remote peer.
+		// If the network is post-merge, use either the last announced finalized
+		// block as the ancient limit, or if we haven't yet received one, the head-
+		// a max fork ancestry limit. One quirky case if we've already passed the
+		// finalized block, in which case the skeleton.Bounds will return nil and
+		// we'll revert to head - 90K. That's fine, we're finishing sync anyway.
 		//
-		// The reason for picking checkpoint first is that a malicious peer can give us
-		// a fake (very high) height, forcing the ancient limit to also be very high.
-		// The peer would start to feed us valid blocks until head, resulting in all of
-		// the blocks might be written into the ancient store. A following mini-reorg
-		// could cause issues.
-		if d.checkpoint != 0 && d.checkpoint > fullMaxForkAncestry+1 {
-			d.ancientLimit = d.checkpoint
-		} else if height > fullMaxForkAncestry+1 {
-			d.ancientLimit = height - fullMaxForkAncestry - 1
+		// For non-merged networks, if there is a checkpoint available, then calculate
+		// the ancientLimit through that. Otherwise calculate the ancient limit through
+		// the advertised height of the remote peer. This most is mostly a fallback for
+		// legacy networks, but should eventually be droppped. TODO(karalabe).
+		if beaconMode {
+			// Beacon sync, use the latest finalized block as the ancient limit
+			// or a reasonable height if no finalized block is yet announced.
+			if final != nil {
+				d.ancientLimit = final.Number.Uint64()
+			} else if height > fullMaxForkAncestry+1 {
+				d.ancientLimit = height - fullMaxForkAncestry - 1
+			} else {
+				d.ancientLimit = 0
+			}
 		} else {
-			d.ancientLimit = 0
+			// Legacy sync, use any hardcoded checkpoints or the best announcement
+			// we have from the remote peer. TODO(karalabe): Drop this pathway.
+			if d.checkpoint != 0 && d.checkpoint > fullMaxForkAncestry+1 {
+				d.ancientLimit = d.checkpoint
+			} else if height > fullMaxForkAncestry+1 {
+				d.ancientLimit = height - fullMaxForkAncestry - 1
+			} else {
+				d.ancientLimit = 0
+			}
 		}
 		frozen, _ := d.stateDB.Ancients() // Ignore the error here since light client can also hit here.
 
@@ -1566,7 +1581,7 @@ func (d *Downloader) importBlockResults(results []*fetchResult) error {
 
 			// In post-merge, notify the engine API of encountered bad chains
 			if d.badBlock != nil {
-				head, _, err := d.skeleton.Bounds()
+				head, _, _, err := d.skeleton.Bounds()
 				if err != nil {
 					log.Error("Failed to retrieve beacon bounds for bad block reporting", "err", err)
 				} else {
@@ -1860,7 +1875,7 @@ func (d *Downloader) reportSnapSyncProgress(force bool) {
 		return
 	}
 	// Retrieve the current chain head and calculate the ETA
-	latest, _, err := d.skeleton.Bounds()
+	latest, _, _, err := d.skeleton.Bounds()
 	if err != nil {
 		// We're going to cheat for non-merged networks, but that's fine
 		latest = d.pivotHeader

eth/downloader/downloader_test.go

@@ -1478,7 +1478,7 @@ func testBeaconSync(t *testing.T, protocol uint, mode SyncMode) {
 			if c.local > 0 {
 				tester.chain.InsertChain(chain.blocks[1 : c.local+1])
 			}
-			if err := tester.downloader.BeaconSync(mode, chain.blocks[len(chain.blocks)-1].Header()); err != nil {
+			if err := tester.downloader.BeaconSync(mode, chain.blocks[len(chain.blocks)-1].Header(), nil); err != nil {
 				t.Fatalf("Failed to beacon sync chain %v %v", c.name, err)
 			}
 			select {

eth/downloader/skeleton.go

@@ -102,13 +102,15 @@ type subchain struct {
 // suspended skeleton sync without prior knowledge of all prior suspension points.
 type skeletonProgress struct {
 	Subchains []*subchain // Disjoint subchains downloaded until now
+	Finalized *uint64     // Last known finalized block number
 }
 
 // headUpdate is a notification that the beacon sync should switch to a new target.
 // The update might request whether to forcefully change the target, or only try to
 // extend it and fail if it's not possible.
 type headUpdate struct {
 	header *types.Header // Header to update the sync target to
+	final  *types.Header // Finalized header to use as thresholds
 	force  bool          // Whether to force the update or only extend if possible
 	errc   chan error    // Channel to signal acceptance of the new head
 }
@@ -321,12 +323,12 @@ func (s *skeleton) Terminate() error {
 //
 // This method does not block, rather it just waits until the syncer receives the
 // fed header. What the syncer does with it is the syncer's problem.
-func (s *skeleton) Sync(head *types.Header, force bool) error {
+func (s *skeleton) Sync(head *types.Header, final *types.Header, force bool) error {
 	log.Trace("New skeleton head announced", "number", head.Number, "hash", head.Hash(), "force", force)
 	errc := make(chan error)
 
 	select {
-	case s.headEvents <- &headUpdate{header: head, force: force, errc: errc}:
+	case s.headEvents <- &headUpdate{header: head, final: final, force: force, errc: errc}:
 		return <-errc
 	case <-s.terminated:
 		return errTerminated
@@ -437,7 +439,7 @@ func (s *skeleton) sync(head *types.Header) (*types.Header, error) {
 			// we don't seamlessly integrate reorgs to keep things simple. If the
 			// network starts doing many mini reorgs, it might be worthwhile handling
 			// a limited depth without an error.
-			if reorged := s.processNewHead(event.header, event.force); reorged {
+			if reorged := s.processNewHead(event.header, event.final, event.force); reorged {
 				// If a reorg is needed, and we're forcing the new head, signal
 				// the syncer to tear down and start over. Otherwise, drop the
 				// non-force reorg.
@@ -590,7 +592,17 @@ func (s *skeleton) saveSyncStatus(db ethdb.KeyValueWriter) {
 // accepts and integrates it into the skeleton or requests a reorg. Upon reorg,
 // the syncer will tear itself down and restart with a fresh head. It is simpler
 // to reconstruct the sync state than to mutate it and hope for the best.
-func (s *skeleton) processNewHead(head *types.Header, force bool) bool {
+func (s *skeleton) processNewHead(head *types.Header, final *types.Header, force bool) bool {
+	// If a new finalized block was announced, update the sync process independent
+	// of what happens with the sync head below
+	if final != nil {
+		if number := final.Number.Uint64(); s.progress.Finalized == nil || *s.progress.Finalized != number {
+			s.progress.Finalized = new(uint64)
+			*s.progress.Finalized = final.Number.Uint64()
+
+			s.saveSyncStatus(s.db)
+		}
+	}
 	// If the header cannot be inserted without interruption, return an error for
 	// the outer loop to tear down the skeleton sync and restart it
 	number := head.Number.Uint64()
@@ -1150,38 +1162,45 @@ func (s *skeleton) cleanStales(filled *types.Header) error {
 	return nil
 }
 
-// Bounds retrieves the current head and tail tracked by the skeleton syncer.
-// This method is used by the backfiller, whose life cycle is controlled by the
-// skeleton syncer.
+// Bounds retrieves the current head and tail tracked by the skeleton syncer
+// and optionally the last known finalized header if any was announced and if
+// it is still in the sync range. This method is used by the backfiller, whose
+// life cycle is controlled by the skeleton syncer.
 //
 // Note, the method will not use the internal state of the skeleton, but will
 // rather blindly pull stuff from the database. This is fine, because the back-
 // filler will only run when the skeleton chain is fully downloaded and stable.
 // There might be new heads appended, but those are atomic from the perspective
 // of this method. Any head reorg will first tear down the backfiller and only
 // then make the modification.
-func (s *skeleton) Bounds() (head *types.Header, tail *types.Header, err error) {
+func (s *skeleton) Bounds() (head *types.Header, tail *types.Header, final *types.Header, err error) {
 	// Read the current sync progress from disk and figure out the current head.
 	// Although there's a lot of error handling here, these are mostly as sanity
 	// checks to avoid crashing if a programming error happens. These should not
 	// happen in live code.
 	status := rawdb.ReadSkeletonSyncStatus(s.db)
 	if len(status) == 0 {
-		return nil, nil, errors.New("beacon sync not yet started")
+		return nil, nil, nil, errors.New("beacon sync not yet started")
 	}
 	progress := new(skeletonProgress)
 	if err := json.Unmarshal(status, progress); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	head = rawdb.ReadSkeletonHeader(s.db, progress.Subchains[0].Head)
 	if head == nil {
-		return nil, nil, fmt.Errorf("head skeleton header %d is missing", progress.Subchains[0].Head)
+		return nil, nil, nil, fmt.Errorf("head skeleton header %d is missing", progress.Subchains[0].Head)
 	}
 	tail = rawdb.ReadSkeletonHeader(s.db, progress.Subchains[0].Tail)
 	if tail == nil {
-		return nil, nil, fmt.Errorf("tail skeleton header %d is missing", progress.Subchains[0].Tail)
+		return nil, nil, nil, fmt.Errorf("tail skeleton header %d is missing", progress.Subchains[0].Tail)
+	}
+	if progress.Finalized != nil && tail.Number.Uint64() <= *progress.Finalized && *progress.Finalized <= head.Number.Uint64() {
+		final = rawdb.ReadSkeletonHeader(s.db, *progress.Finalized)
+		if final == nil {
+			return nil, nil, nil, fmt.Errorf("finalized skeleton header %d is missing", *progress.Finalized)
+		}
 	}
-	return head, tail, nil
+	return head, tail, final, nil
 }
 
 // Header retrieves a specific header tracked by the skeleton syncer. This method

eth/downloader/skeleton_test.go

@@ -370,7 +370,7 @@ func TestSkeletonSyncInit(t *testing.T) {
 
 		skeleton := newSkeleton(db, newPeerSet(), nil, newHookedBackfiller())
 		skeleton.syncStarting = func() { close(wait) }
-		skeleton.Sync(tt.head, true)
+		skeleton.Sync(tt.head, nil, true)
 
 		<-wait
 		skeleton.Terminate()
@@ -484,10 +484,10 @@ func TestSkeletonSyncExtend(t *testing.T) {
 
 		skeleton := newSkeleton(db, newPeerSet(), nil, newHookedBackfiller())
 		skeleton.syncStarting = func() { close(wait) }
-		skeleton.Sync(tt.head, true)
+		skeleton.Sync(tt.head, nil, true)
 
 		<-wait
-		if err := skeleton.Sync(tt.extend, false); err != tt.err {
+		if err := skeleton.Sync(tt.extend, nil, false); err != tt.err {
 			t.Errorf("test %d: extension failure mismatch: have %v, want %v", i, err, tt.err)
 		}
 		skeleton.Terminate()
@@ -859,7 +859,7 @@ func TestSkeletonSyncRetrievals(t *testing.T) {
 		}
 		// Create a skeleton sync and run a cycle
 		skeleton := newSkeleton(db, peerset, drop, filler)
-		skeleton.Sync(tt.head, true)
+		skeleton.Sync(tt.head, nil, true)
 
 		var progress skeletonProgress
 		// Wait a bit (bleah) for the initial sync loop to go to idle. This might
@@ -910,7 +910,7 @@ func TestSkeletonSyncRetrievals(t *testing.T) {
 		}
 		// Apply the post-init events if there's any
 		if tt.newHead != nil {
-			skeleton.Sync(tt.newHead, true)
+			skeleton.Sync(tt.newHead, nil, true)
 		}
 		if tt.newPeer != nil {
 			if err := peerset.Register(newPeerConnection(tt.newPeer.id, eth.ETH66, tt.newPeer, log.New("id", tt.newPeer.id))); err != nil {