Block backfilling (#12968)

* backfill service

* fix bug where origin state is never unlocked

* support mvslice states

* use renamed interface

* refactor db code to skip block cache for backfill

* lint

* add test for verifier.verify

* enable service in service init test

* cancellation cleanup

* adding nil checks to configset juggling

* assume blocks are available by default

As long as we're sure the AvailableBlocker is initialized correctly
during node startup, defaulting to assuming we aren't in a checkpoint
sync simplifies things greatly for tests.

* block saving path refactor and bugfix

* fix fillback test

* fix BackfillStatus init tests

---------

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

beacon-chain/core/helpers/weak_subjectivity.go

@@ -202,3 +202,14 @@ func ParseWeakSubjectivityInputString(wsCheckpointString string) (*v1alpha1.Chec
 		Root:  bRoot,
 	}, nil
 }
+
+// MinEpochsForBlockRequests computes the number of epochs of block history that we need to maintain,
+// relative to the current epoch, per the p2p specs. This is used to compute the slot where backfill is complete.
+// value defined:
+// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/p2p-interface.md#configuration
+// MIN_VALIDATOR_WITHDRAWABILITY_DELAY + CHURN_LIMIT_QUOTIENT // 2 (= 33024, ~5 months)
+// detailed rationale: https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/p2p-interface.md#why-are-blocksbyrange-requests-only-required-to-be-served-for-the-latest-min_epochs_for_block_requests-epochs
+func MinEpochsForBlockRequests() primitives.Epoch {
+	return params.BeaconConfig().MinValidatorWithdrawabilityDelay +
+		primitives.Epoch(params.BeaconConfig().ChurnLimitQuotient/2)
+}

beacon-chain/core/helpers/weak_subjectivity_test.go

@@ -281,3 +281,19 @@ func genState(t *testing.T, valCount, avgBalance uint64) state.BeaconState {
 
 	return beaconState
 }
+
+func TestMinEpochsForBlockRequests(t *testing.T) {
+	params.SetActiveTestCleanup(t, params.MainnetConfig())
+	var expected primitives.Epoch = 33024
+	// expected value of 33024 via spec commentary:
+	// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/p2p-interface.md#why-are-blocksbyrange-requests-only-required-to-be-served-for-the-latest-min_epochs_for_block_requests-epochs
+	//	MIN_EPOCHS_FOR_BLOCK_REQUESTS is calculated using the arithmetic from compute_weak_subjectivity_period found in the weak subjectivity guide. Specifically to find this max epoch range, we use the worst case event of a very large validator size (>= MIN_PER_EPOCH_CHURN_LIMIT * CHURN_LIMIT_QUOTIENT).
+	//
+	//	MIN_EPOCHS_FOR_BLOCK_REQUESTS = (
+	//	    MIN_VALIDATOR_WITHDRAWABILITY_DELAY
+	//	    + MAX_SAFETY_DECAY * CHURN_LIMIT_QUOTIENT // (2 * 100)
+	//	)
+	//
+	//	Where MAX_SAFETY_DECAY = 100 and thus MIN_EPOCHS_FOR_BLOCK_REQUESTS = 33024 (~5 months).
+	require.Equal(t, expected, helpers.MinEpochsForBlockRequests())
+}

beacon-chain/db/errors.go

@@ -22,9 +22,6 @@ var ErrNotFoundOriginBlockRoot = kv.ErrNotFoundOriginBlockRoot
 // ErrNotFoundBackfillBlockRoot wraps ErrNotFound for an error specific to the backfill block root.
 var ErrNotFoundBackfillBlockRoot = kv.ErrNotFoundBackfillBlockRoot
 
-// ErrNotFoundGenesisBlockRoot means no genesis block root was found, indicating the db was not initialized with genesis
-var ErrNotFoundGenesisBlockRoot = kv.ErrNotFoundGenesisBlockRoot
-
 // IsNotFound allows callers to treat errors from a flat-file database, where the file record is missing,
 // as equivalent to db.ErrNotFound.
 func IsNotFound(err error) bool {

beacon-chain/db/iface/BUILD.bazel

@@ -13,9 +13,11 @@ go_library(
         "//beacon-chain/db/filters:go_default_library",
         "//beacon-chain/slasher/types:go_default_library",
         "//beacon-chain/state:go_default_library",
+        "//consensus-types/blocks:go_default_library",
         "//consensus-types/interfaces:go_default_library",
         "//consensus-types/primitives:go_default_library",
         "//monitoring/backup:go_default_library",
+        "//proto/dbval:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",
         "@com_github_ethereum_go_ethereum//common:go_default_library",
     ],

beacon-chain/db/iface/interface.go

@@ -11,9 +11,11 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db/filters"
 	slashertypes "github.com/prysmaticlabs/prysm/v4/beacon-chain/slasher/types"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
 	"github.com/prysmaticlabs/prysm/v4/monitoring/backup"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
 	ethpb "github.com/prysmaticlabs/prysm/v4/proto/prysm/v1alpha1"
 )
 
@@ -57,7 +59,7 @@ type ReadOnlyDatabase interface {
 
 	// origin checkpoint sync support
 	OriginCheckpointBlockRoot(ctx context.Context) ([32]byte, error)
-	BackfillBlockRoot(ctx context.Context) ([32]byte, error)
+	BackfillStatus(context.Context) (*dbval.BackfillStatus, error)
 }
 
 // NoHeadAccessDatabase defines a struct without access to chain head data.
@@ -68,6 +70,7 @@ type NoHeadAccessDatabase interface {
 	DeleteBlock(ctx context.Context, root [32]byte) error
 	SaveBlock(ctx context.Context, block interfaces.ReadOnlySignedBeaconBlock) error
 	SaveBlocks(ctx context.Context, blocks []interfaces.ReadOnlySignedBeaconBlock) error
+	SaveROBlocks(ctx context.Context, blks []blocks.ROBlock, cache bool) error
 	SaveGenesisBlockRoot(ctx context.Context, blockRoot [32]byte) error
 	// State related methods.
 	SaveState(ctx context.Context, state state.ReadOnlyBeaconState, blockRoot [32]byte) error
@@ -106,9 +109,10 @@ type HeadAccessDatabase interface {
 	SaveGenesisData(ctx context.Context, state state.BeaconState) error
 	EnsureEmbeddedGenesis(ctx context.Context) error
 
-	// initialization method needed for origin checkpoint sync
+	// Support for checkpoint sync and backfill.
 	SaveOrigin(ctx context.Context, serState, serBlock []byte) error
-	SaveBackfillBlockRoot(ctx context.Context, blockRoot [32]byte) error
+	SaveBackfillStatus(context.Context, *dbval.BackfillStatus) error
+	BackfillFinalizedIndex(ctx context.Context, blocks []blocks.ROBlock, finalizedChildRoot [32]byte) error
 }
 
 // SlasherDatabase interface for persisting data related to detecting slashable offenses on Ethereum.

beacon-chain/db/kv/BUILD.bazel

@@ -4,6 +4,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "archived_point.go",
+        "backfill.go",
         "backup.go",
         "blocks.go",
         "checkpoint.go",
@@ -48,6 +49,7 @@ go_library(
         "//io/file:go_default_library",
         "//monitoring/progress:go_default_library",
         "//monitoring/tracing:go_default_library",
+        "//proto/dbval:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",
         "//runtime/version:go_default_library",
         "//time:go_default_library",
@@ -73,6 +75,7 @@ go_test(
     name = "go_default_test",
     srcs = [
         "archived_point_test.go",
+        "backfill_test.go",
         "backup_test.go",
         "blocks_test.go",
         "checkpoint_test.go",
@@ -107,6 +110,7 @@ go_test(
         "//consensus-types/interfaces:go_default_library",
         "//consensus-types/primitives:go_default_library",
         "//encoding/bytesutil:go_default_library",
+        "//proto/dbval:go_default_library",
         "//proto/engine/v1:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",
         "//proto/testing:go_default_library",

beacon-chain/db/kv/backfill.go

@@ -0,0 +1,44 @@
+package kv
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
+	bolt "go.etcd.io/bbolt"
+	"go.opencensus.io/trace"
+	"google.golang.org/protobuf/proto"
+)
+
+// SaveBackfillStatus encodes the given BackfillStatus protobuf struct and writes it to a single key in the db.
+// This value is used by the backfill service to keep track of the range of blocks that need to be synced. It is also used by the
+// code that serves blocks or regenerates states to keep track of what range of blocks are available.
+func (s *Store) SaveBackfillStatus(ctx context.Context, bf *dbval.BackfillStatus) error {
+	_, span := trace.StartSpan(ctx, "BeaconDB.SaveBackfillStatus")
+	defer span.End()
+	bfb, err := proto.Marshal(bf)
+	if err != nil {
+		return err
+	}
+	return s.db.Update(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(blocksBucket)
+		return bucket.Put(backfillStatusKey, bfb)
+	})
+}
+
+// BackfillStatus retrieves the most recently saved version of the BackfillStatus protobuf struct.
+// This is used to persist information about backfill status across restarts.
+func (s *Store) BackfillStatus(ctx context.Context) (*dbval.BackfillStatus, error) {
+	_, span := trace.StartSpan(ctx, "BeaconDB.BackfillStatus")
+	defer span.End()
+	bf := &dbval.BackfillStatus{}
+	err := s.db.View(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(blocksBucket)
+		bs := bucket.Get(backfillStatusKey)
+		if len(bs) == 0 {
+			return errors.Wrap(ErrNotFound, "BackfillStatus not found")
+		}
+		return proto.Unmarshal(bs, bf)
+	})
+	return bf, err
+}

beacon-chain/db/kv/backfill_test.go

@@ -0,0 +1,35 @@
+package kv
+
+import (
+	"context"
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+	"google.golang.org/protobuf/proto"
+)
+
+func TestBackfillRoundtrip(t *testing.T) {
+	db := setupDB(t)
+	b := &dbval.BackfillStatus{}
+	b.LowSlot = 23
+	b.LowRoot = bytesutil.PadTo([]byte("low"), 32)
+	b.LowParentRoot = bytesutil.PadTo([]byte("parent"), 32)
+	m, err := proto.Marshal(b)
+	require.NoError(t, err)
+	ub := &dbval.BackfillStatus{}
+	require.NoError(t, proto.Unmarshal(m, ub))
+	require.Equal(t, b.LowSlot, ub.LowSlot)
+	require.DeepEqual(t, b.LowRoot, ub.LowRoot)
+	require.DeepEqual(t, b.LowParentRoot, ub.LowParentRoot)
+
+	ctx := context.Background()
+	require.NoError(t, db.SaveBackfillStatus(ctx, b))
+	dbub, err := db.BackfillStatus(ctx)
+	require.NoError(t, err)
+
+	require.Equal(t, b.LowSlot, dbub.LowSlot)
+	require.DeepEqual(t, b.LowRoot, dbub.LowRoot)
+	require.DeepEqual(t, b.LowParentRoot, dbub.LowParentRoot)
+}

beacon-chain/db/kv/blocks.go

@@ -70,25 +70,6 @@ func (s *Store) OriginCheckpointBlockRoot(ctx context.Context) ([32]byte, error)
 	return root, err
 }
 
-// BackfillBlockRoot keeps track of the highest block available before the OriginCheckpointBlockRoot
-func (s *Store) BackfillBlockRoot(ctx context.Context) ([32]byte, error) {
-	_, span := trace.StartSpan(ctx, "BeaconDB.BackfillBlockRoot")
-	defer span.End()
-
-	var root [32]byte
-	err := s.db.View(func(tx *bolt.Tx) error {
-		bkt := tx.Bucket(blocksBucket)
-		rootSlice := bkt.Get(backfillBlockRootKey)
-		if len(rootSlice) == 0 {
-			return ErrNotFoundBackfillBlockRoot
-		}
-		root = bytesutil.ToBytes32(rootSlice)
-		return nil
-	})
-
-	return root, err
-}
-
 // HeadBlock returns the latest canonical block in the Ethereum Beacon Chain.
 func (s *Store) HeadBlock(ctx context.Context) (interfaces.ReadOnlySignedBeaconBlock, error) {
 	ctx, span := trace.StartSpan(ctx, "BeaconDB.HeadBlock")
@@ -292,55 +273,95 @@ func (s *Store) SaveBlocks(ctx context.Context, blks []interfaces.ReadOnlySigned
 	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveBlocks")
 	defer span.End()
 
-	// Performing marshaling, hashing, and indexing outside the bolt transaction
-	// to minimize the time we hold the DB lock.
-	blockRoots := make([][]byte, len(blks))
-	encodedBlocks := make([][]byte, len(blks))
-	indicesForBlocks := make([]map[string][]byte, len(blks))
-	for i, blk := range blks {
-		blockRoot, err := blk.Block().HashTreeRoot()
+	robs := make([]blocks.ROBlock, len(blks))
+	for i := range blks {
+		rb, err := blocks.NewROBlock(blks[i])
 		if err != nil {
-			return err
+			return errors.Wrapf(err, "failed to make an ROBlock for a block in SaveBlocks")
 		}
-		enc, err := s.marshalBlock(ctx, blk)
-		if err != nil {
-			return err
-		}
-		blockRoots[i] = blockRoot[:]
-		encodedBlocks[i] = enc
-		indicesByBucket := createBlockIndicesFromBlock(ctx, blk.Block())
-		indicesForBlocks[i] = indicesByBucket
+		robs[i] = rb
 	}
-	saveBlinded, err := s.shouldSaveBlinded(ctx)
+	return s.SaveROBlocks(ctx, robs, true)
+}
+
+type blockBatchEntry struct {
+	root    []byte
+	block   interfaces.ReadOnlySignedBeaconBlock
+	enc     []byte
+	updated bool
+	indices map[string][]byte
+}
+
+func prepareBlockBatch(blks []blocks.ROBlock, shouldBlind bool) ([]blockBatchEntry, error) {
+	batch := make([]blockBatchEntry, len(blks))
+	for i := range blks {
+		batch[i].root, batch[i].block = blks[i].RootSlice(), blks[i].ReadOnlySignedBeaconBlock
+		batch[i].indices = blockIndices(batch[i].block.Block().Slot(), batch[i].block.Block().ParentRoot())
+		if shouldBlind {
+			blinded, err := batch[i].block.ToBlinded()
+			if err != nil {
+				if !errors.Is(err, blocks.ErrUnsupportedVersion) {
+					return nil, errors.Wrapf(err, "could not convert block to blinded format for root %#x", batch[i].root)
+				}
+				// Pre-deneb blocks give ErrUnsupportedVersion; use the full block already in the batch entry.
+			} else {
+				batch[i].block = blinded
+			}
+		}
+		enc, err := encodeBlock(batch[i].block)
+		if err != nil {
+			return nil, errors.Wrapf(err, "failed to encode block for root %#x", batch[i].root)
+		}
+		batch[i].enc = enc
+	}
+	return batch, nil
+}
+
+func (s *Store) SaveROBlocks(ctx context.Context, blks []blocks.ROBlock, cache bool) error {
+	shouldBlind, err := s.shouldSaveBlinded(ctx)
 	if err != nil {
 		return err
 	}
-	return s.db.Update(func(tx *bolt.Tx) error {
+	// Precompute expensive values outside the db transaction.
+	batch, err := prepareBlockBatch(blks, shouldBlind)
+	if err != nil {
+		return errors.Wrap(err, "failed to encode all blocks in batch for saving to the db")
+	}
+	err = s.db.Update(func(tx *bolt.Tx) error {
 		bkt := tx.Bucket(blocksBucket)
-		for i, blk := range blks {
-			if existingBlock := bkt.Get(blockRoots[i]); existingBlock != nil {
+		for i := range batch {
+			if exists := bkt.Get(batch[i].root); exists != nil {
 				continue
 			}
-			if err := updateValueForIndices(ctx, indicesForBlocks[i], blockRoots[i], tx); err != nil {
-				return errors.Wrap(err, "could not update DB indices")
+			if err := bkt.Put(batch[i].root, batch[i].enc); err != nil {
+				return errors.Wrapf(err, "could write block to db with root %#x", batch[i].root)
 			}
-			if saveBlinded {
-				blindedBlock, err := blk.ToBlinded()
-				if err != nil {
-					if !errors.Is(err, blocks.ErrUnsupportedVersion) {
-						return err
-					}
-				} else {
-					blk = blindedBlock
-				}
-			}
-			s.blockCache.Set(string(blockRoots[i]), blk, int64(len(encodedBlocks[i])))
-			if err := bkt.Put(blockRoots[i], encodedBlocks[i]); err != nil {
-				return err
+			if err := updateValueForIndices(ctx, batch[i].indices, batch[i].root, tx); err != nil {
+				return errors.Wrapf(err, "could not update DB indices for root %#x", batch[i].root)
 			}
+			batch[i].updated = true
 		}
 		return nil
 	})
+	if !cache {
+		return err
+	}
+	for i := range batch {
+		if batch[i].updated {
+			s.blockCache.Set(string(batch[i].root), batch[i].block, int64(len(batch[i].enc)))
+		}
+	}
+	return err
+}
+
+// blockIndices takes in a beacon block and returns
+// a map of bolt DB index buckets corresponding to each particular key for indices for
+// data, such as (shard indices bucket -> shard 5).
+func blockIndices(slot primitives.Slot, parentRoot [32]byte) map[string][]byte {
+	return map[string][]byte{
+		string(blockSlotIndicesBucket):       bytesutil.SlotToBytesBigEndian(slot),
+		string(blockParentRootIndicesBucket): parentRoot[:],
+	}
 }
 
 // SaveHeadBlockRoot to the db.
@@ -417,17 +438,6 @@ func (s *Store) SaveOriginCheckpointBlockRoot(ctx context.Context, blockRoot [32
 	})
 }
 
-// SaveBackfillBlockRoot is used to keep track of the most recently backfilled block root when
-// the node was initialized via checkpoint sync.
-func (s *Store) SaveBackfillBlockRoot(ctx context.Context, blockRoot [32]byte) error {
-	_, span := trace.StartSpan(ctx, "BeaconDB.SaveBackfillBlockRoot")
-	defer span.End()
-	return s.db.Update(func(tx *bolt.Tx) error {
-		bucket := tx.Bucket(blocksBucket)
-		return bucket.Put(backfillBlockRootKey, blockRoot[:])
-	})
-}
-
 // HighestRootsBelowSlot returns roots from the database slot index from the highest slot below the input slot.
 // The slot value at the beginning of the return list is the slot where the roots were found. This is helpful so that
 // calling code can make decisions based on the slot without resolving the blocks to discover their slot (for instance
@@ -726,31 +736,6 @@ func blockRootsBySlot(ctx context.Context, tx *bolt.Tx, slot primitives.Slot) ([
 	return [][32]byte{}, nil
 }
 
-// createBlockIndicesFromBlock takes in a beacon block and returns
-// a map of bolt DB index buckets corresponding to each particular key for indices for
-// data, such as (shard indices bucket -> shard 5).
-func createBlockIndicesFromBlock(ctx context.Context, block interfaces.ReadOnlyBeaconBlock) map[string][]byte {
-	_, span := trace.StartSpan(ctx, "BeaconDB.createBlockIndicesFromBlock")
-	defer span.End()
-	indicesByBucket := make(map[string][]byte)
-	// Every index has a unique bucket for fast, binary-search
-	// range scans for filtering across keys.
-	buckets := [][]byte{
-		blockSlotIndicesBucket,
-	}
-	indices := [][]byte{
-		bytesutil.SlotToBytesBigEndian(block.Slot()),
-	}
-	buckets = append(buckets, blockParentRootIndicesBucket)
-	parentRoot := block.ParentRoot()
-	indices = append(indices, parentRoot[:])
-
-	for i := 0; i < len(buckets); i++ {
-		indicesByBucket[string(buckets[i])] = indices[i]
-	}
-	return indicesByBucket
-}
-
 // createBlockFiltersFromIndices takes in filter criteria and returns
 // a map with a single key-value pair: "block-parent-root-indices” -> parentRoot (array of bytes).
 //
@@ -838,74 +823,44 @@ func unmarshalBlock(_ context.Context, enc []byte) (interfaces.ReadOnlySignedBea
 	return blocks.NewSignedBeaconBlock(rawBlock)
 }
 
-func (s *Store) marshalBlock(
-	ctx context.Context,
-	blk interfaces.ReadOnlySignedBeaconBlock,
-) ([]byte, error) {
-	shouldBlind, err := s.shouldSaveBlinded(ctx)
+func encodeBlock(blk interfaces.ReadOnlySignedBeaconBlock) ([]byte, error) {
+	key, err := keyForBlock(blk)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err, "could not determine version encoding key for block")
 	}
-	if shouldBlind {
-		return marshalBlockBlinded(ctx, blk)
+	enc, err := blk.MarshalSSZ()
+	if err != nil {
+		return nil, errors.Wrap(err, "could not marshal block")
 	}
-	return marshalBlockFull(ctx, blk)
+	dbfmt := make([]byte, len(key)+len(enc))
+	if len(key) > 0 {
+		copy(dbfmt, key)
+	}
+	copy(dbfmt[len(key):], enc)
+	return snappy.Encode(nil, dbfmt), nil
 }
 
-// Encodes a full beacon block to the DB with its associated key.
-func marshalBlockFull(
-	_ context.Context,
-	blk interfaces.ReadOnlySignedBeaconBlock,
-) ([]byte, error) {
-	var encodedBlock []byte
-	var err error
-	encodedBlock, err = blk.MarshalSSZ()
-	if err != nil {
-		return nil, err
-	}
+func keyForBlock(blk interfaces.ReadOnlySignedBeaconBlock) ([]byte, error) {
 	switch blk.Version() {
 	case version.Deneb:
-		return snappy.Encode(nil, append(denebKey, encodedBlock...)), nil
-	case version.Capella:
-		return snappy.Encode(nil, append(capellaKey, encodedBlock...)), nil
-	case version.Bellatrix:
-		return snappy.Encode(nil, append(bellatrixKey, encodedBlock...)), nil
-	case version.Altair:
-		return snappy.Encode(nil, append(altairKey, encodedBlock...)), nil
-	case version.Phase0:
-		return snappy.Encode(nil, encodedBlock), nil
-	default:
-		return nil, errors.New("unknown block version")
-	}
-}
-
-// Encodes a blinded beacon block with its associated key.
-// If the block does not support blinding, we then encode it as a full
-// block with its associated key by calling marshalBlockFull.
-func marshalBlockBlinded(
-	ctx context.Context,
-	blk interfaces.ReadOnlySignedBeaconBlock,
-) ([]byte, error) {
-	blindedBlock, err := blk.ToBlinded()
-	if err != nil {
-		switch {
-		case errors.Is(err, blocks.ErrUnsupportedVersion):
-			return marshalBlockFull(ctx, blk)
-		default:
-			return nil, errors.Wrap(err, "could not convert block to blinded format")
+		if blk.IsBlinded() {
+			return denebBlindKey, nil
 		}
-	}
-	encodedBlock, err := blindedBlock.MarshalSSZ()
-	if err != nil {
-		return nil, errors.Wrap(err, "could not marshal blinded block")
-	}
-	switch blk.Version() {
-	case version.Deneb:
-		return snappy.Encode(nil, append(denebBlindKey, encodedBlock...)), nil
+		return denebKey, nil
 	case version.Capella:
-		return snappy.Encode(nil, append(capellaBlindKey, encodedBlock...)), nil
+		if blk.IsBlinded() {
+			return capellaBlindKey, nil
+		}
+		return capellaKey, nil
 	case version.Bellatrix:
-		return snappy.Encode(nil, append(bellatrixBlindKey, encodedBlock...)), nil
+		if blk.IsBlinded() {
+			return bellatrixBlindKey, nil
+		}
+		return bellatrixKey, nil
+	case version.Altair:
+		return altairKey, nil
+	case version.Phase0:
+		return nil, nil
 	default:
 		return nil, fmt.Errorf("unsupported block version: %v", blk.Version())
 	}

beacon-chain/db/kv/blocks_test.go

@@ -126,23 +126,6 @@ var blockTests = []struct {
 	},
 }
 
-func TestStore_SaveBackfillBlockRoot(t *testing.T) {
-	db := setupDB(t)
-	ctx := context.Background()
-
-	_, err := db.BackfillBlockRoot(ctx)
-	require.ErrorIs(t, err, ErrNotFoundBackfillBlockRoot)
-
-	var expected [32]byte
-	copy(expected[:], []byte{0x23})
-	err = db.SaveBackfillBlockRoot(ctx, expected)
-	require.NoError(t, err)
-	actual, err := db.BackfillBlockRoot(ctx)
-	require.NoError(t, err)
-	require.Equal(t, expected, actual)
-
-}
-
 func TestStore_SaveBlock_NoDuplicates(t *testing.T) {
 	BlockCacheSize = 1
 	slot := primitives.Slot(20)

beacon-chain/db/kv/error.go

@@ -21,3 +21,8 @@ var ErrNotFoundBackfillBlockRoot = errors.Wrap(ErrNotFound, "BackfillBlockRoot")
 
 // ErrNotFoundFeeRecipient is a not found error specifically for the fee recipient getter
 var ErrNotFoundFeeRecipient = errors.Wrap(ErrNotFound, "fee recipient")
+
+var errEmptyBlockSlice = errors.New("[]blocks.ROBlock is empty")
+var errIncorrectBlockParent = errors.New("unexpected missing or forked blocks in a []ROBlock")
+var errFinalizedChildNotFound = errors.New("unable to find finalized root descending from backfill batch")
+var errNotConnectedToFinalized = errors.New("unable to finalize backfill blocks, finalized parent_root does not match")

beacon-chain/db/kv/finalized_block_roots.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 
+	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db/filters"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
@@ -163,6 +164,83 @@ func (s *Store) updateFinalizedBlockRoots(ctx context.Context, tx *bolt.Tx, chec
 	return bkt.Put(previousFinalizedCheckpointKey, enc)
 }
 
+// BackfillFinalizedIndex updates the finalized index for a contiguous chain of blocks that are the ancestors of the
+// given finalized child root. This is needed to update the finalized index during backfill, because the usual
+// updateFinalizedBlockRoots has assumptions that are incompatible with backfill processing.
+func (s *Store) BackfillFinalizedIndex(ctx context.Context, blocks []blocks.ROBlock, finalizedChildRoot [32]byte) error {
+	ctx, span := trace.StartSpan(ctx, "BeaconDB.BackfillFinalizedIndex")
+	defer span.End()
+	if len(blocks) == 0 {
+		return errEmptyBlockSlice
+	}
+
+	fbrs := make([]*ethpb.FinalizedBlockRootContainer, len(blocks))
+	encs := make([][]byte, len(blocks))
+	for i := range blocks {
+		pr := blocks[i].Block().ParentRoot()
+		fbrs[i] = &ethpb.FinalizedBlockRootContainer{
+			ParentRoot: pr[:],
+			// ChildRoot: will be filled in on the next iteration when we look at the descendent block.
+		}
+		if i == 0 {
+			continue
+		}
+		if blocks[i-1].Root() != blocks[i].Block().ParentRoot() {
+			return errors.Wrapf(errIncorrectBlockParent, "previous root=%#x, slot=%d; child parent_root=%#x, root=%#x, slot=%d",
+				blocks[i-1].Root(), blocks[i-1].Block().Slot(), blocks[i].Block().ParentRoot(), blocks[i].Root(), blocks[i].Block().Slot())
+		}
+
+		// We know the previous index is the parent of this one thanks to the assertion above,
+		// so we can set the ChildRoot of the previous value to the root of the current value.
+		fbrs[i-1].ChildRoot = blocks[i].RootSlice()
+		// Now that the value for fbrs[i-1] is complete, perform encoding here to minimize time in Update,
+		// which holds the global db lock.
+		penc, err := encode(ctx, fbrs[i-1])
+		if err != nil {
+			tracing.AnnotateError(span, err)
+			return err
+		}
+		encs[i-1] = penc
+
+		// The final element is the parent of finalizedChildRoot. This is checked inside the db transaction using
+		// the parent_root value stored in the index data for finalizedChildRoot.
+		if i == len(blocks)-1 {
+			fbrs[i].ChildRoot = finalizedChildRoot[:]
+			// Final element is complete, so it is pre-encoded like the others.
+			enc, err := encode(ctx, fbrs[i])
+			if err != nil {
+				tracing.AnnotateError(span, err)
+				return err
+			}
+			encs[i] = enc
+		}
+	}
+
+	return s.db.Update(func(tx *bolt.Tx) error {
+		bkt := tx.Bucket(finalizedBlockRootsIndexBucket)
+		child := bkt.Get(finalizedChildRoot[:])
+		if len(child) == 0 {
+			return errFinalizedChildNotFound
+		}
+		fcc := &ethpb.FinalizedBlockRootContainer{}
+		if err := decode(ctx, child, fcc); err != nil {
+			return errors.Wrapf(err, "unable to decode finalized block root container for root=%#x", finalizedChildRoot)
+		}
+		// Ensure that the existing finalized chain descends from the new segment.
+		if !bytes.Equal(fcc.ParentRoot, blocks[len(blocks)-1].RootSlice()) {
+			return errors.Wrapf(errNotConnectedToFinalized, "finalized block root container for root=%#x has parent_root=%#x, not %#x",
+				finalizedChildRoot, fcc.ParentRoot, blocks[len(blocks)-1].RootSlice())
+		}
+		// Update the finalized index with entries for each block in the new segment.
+		for i := range fbrs {
+			if err := bkt.Put(blocks[i].RootSlice(), encs[i]); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
 // IsFinalizedBlock returns true if the block root is present in the finalized block root index.
 // A beacon block root contained exists in this index if it is considered finalized and canonical.
 // Note: beacon blocks from the latest finalized epoch return true, whether or not they are

beacon-chain/db/kv/finalized_block_roots_test.go

@@ -1,6 +1,7 @@
 package kv
 
 import (
+	"bytes"
 	"context"
 	"testing"
 
@@ -14,6 +15,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/testing/assert"
 	"github.com/prysmaticlabs/prysm/v4/testing/require"
 	"github.com/prysmaticlabs/prysm/v4/testing/util"
+	bolt "go.etcd.io/bbolt"
 )
 
 var genesisBlockRoot = bytesutil.ToBytes32([]byte{'G', 'E', 'N', 'E', 'S', 'I', 'S'})
@@ -234,3 +236,64 @@ func makeBlocksAltair(t *testing.T, startIdx, num uint64, previousRoot [32]byte)
 	}
 	return ifaceBlocks
 }
+
+func TestStore_BackfillFinalizedIndex(t *testing.T) {
+	db := setupDB(t)
+	ctx := context.Background()
+	require.ErrorIs(t, db.BackfillFinalizedIndex(ctx, []consensusblocks.ROBlock{}, [32]byte{}), errEmptyBlockSlice)
+	blks, err := consensusblocks.NewROBlockSlice(makeBlocks(t, 0, 66, [32]byte{}))
+	require.NoError(t, err)
+
+	// set up existing finalized block
+	ebpr := blks[64].Block().ParentRoot()
+	ebr := blks[64].Root()
+	chldr := blks[65].Root()
+	ebf := &ethpb.FinalizedBlockRootContainer{
+		ParentRoot: ebpr[:],
+		ChildRoot:  chldr[:],
+	}
+	disjoint := []consensusblocks.ROBlock{
+		blks[0],
+		blks[2],
+	}
+	enc, err := encode(ctx, ebf)
+	require.NoError(t, err)
+	err = db.db.Update(func(tx *bolt.Tx) error {
+		bkt := tx.Bucket(finalizedBlockRootsIndexBucket)
+		return bkt.Put(ebr[:], enc)
+	})
+
+	// reslice to remove the existing blocks
+	blks = blks[0:64]
+	// check the other error conditions with a descendent root that really doesn't exist
+	require.NoError(t, err)
+	require.ErrorIs(t, db.BackfillFinalizedIndex(ctx, disjoint, [32]byte{}), errIncorrectBlockParent)
+	require.NoError(t, err)
+	require.ErrorIs(t, errFinalizedChildNotFound, db.BackfillFinalizedIndex(ctx, blks, [32]byte{}))
+
+	// use the real root so that it succeeds
+	require.NoError(t, db.BackfillFinalizedIndex(ctx, blks, ebr))
+	for i := range blks {
+		require.NoError(t, db.db.View(func(tx *bolt.Tx) error {
+			bkt := tx.Bucket(finalizedBlockRootsIndexBucket)
+			encfr := bkt.Get(blks[i].RootSlice())
+			require.Equal(t, true, len(encfr) > 0)
+			fr := &ethpb.FinalizedBlockRootContainer{}
+			require.NoError(t, decode(ctx, encfr, fr))
+			require.Equal(t, 32, len(fr.ParentRoot))
+			require.Equal(t, 32, len(fr.ChildRoot))
+			pr := blks[i].Block().ParentRoot()
+			require.Equal(t, true, bytes.Equal(fr.ParentRoot, pr[:]))
+			if i > 0 {
+				require.Equal(t, true, bytes.Equal(fr.ParentRoot, blks[i-1].RootSlice()))
+			}
+			if i < len(blks)-1 {
+				require.DeepEqual(t, fr.ChildRoot, blks[i+1].RootSlice())
+			}
+			if i == len(blks)-1 {
+				require.DeepEqual(t, fr.ChildRoot, ebr[:])
+			}
+			return nil
+		}))
+	}
+}

beacon-chain/db/kv/kv_test.go

@@ -1,6 +1,7 @@
 package kv
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"testing"
@@ -116,13 +117,25 @@ func Test_setupBlockStorageType(t *testing.T) {
 		root, err = wrappedBlock.Block().HashTreeRoot()
 		require.NoError(t, err)
 		require.NoError(t, store.SaveBlock(ctx, wrappedBlock))
-		retrievedBlk, err = store.Block(ctx, root)
-		require.NoError(t, err)
-
-		require.Equal(t, true, retrievedBlk.IsBlinded())
 		wrappedBlinded, err := wrappedBlock.ToBlinded()
 		require.NoError(t, err)
-		require.DeepEqual(t, wrappedBlinded, retrievedBlk)
+
+		retrievedBlk, err = store.Block(ctx, root)
+		require.NoError(t, err)
+		require.Equal(t, true, retrievedBlk.IsBlinded())
+
+		// Compare retrieved value by root, and marshaled bytes.
+		mSrc, err := wrappedBlinded.MarshalSSZ()
+		require.NoError(t, err)
+		mTgt, err := retrievedBlk.MarshalSSZ()
+		require.NoError(t, err)
+		require.Equal(t, true, bytes.Equal(mSrc, mTgt))
+
+		rSrc, err := wrappedBlinded.Block().HashTreeRoot()
+		require.NoError(t, err)
+		rTgt, err := retrievedBlk.Block().HashTreeRoot()
+		require.NoError(t, err)
+		require.Equal(t, rSrc, rTgt)
 	})
 	t.Run("existing database with full blocks type should continue storing full blocks", func(t *testing.T) {
 		store := setupDB(t)
@@ -155,10 +168,21 @@ func Test_setupBlockStorageType(t *testing.T) {
 		root, err = wrappedBlock.Block().HashTreeRoot()
 		require.NoError(t, err)
 		require.NoError(t, store.SaveBlock(ctx, wrappedBlock))
+
 		retrievedBlk, err = store.Block(ctx, root)
 		require.NoError(t, err)
 		require.Equal(t, false, retrievedBlk.IsBlinded())
-		require.DeepEqual(t, wrappedBlock, retrievedBlk)
+
+		// Compare retrieved value by root, and marshaled bytes.
+		mSrc, err := wrappedBlock.MarshalSSZ()
+		require.NoError(t, err)
+		mTgt, err := retrievedBlk.MarshalSSZ()
+		require.NoError(t, err)
+		require.Equal(t, true, bytes.Equal(mSrc, mTgt))
+
+		rTgt, err := retrievedBlk.Block().HashTreeRoot()
+		require.NoError(t, err)
+		require.Equal(t, root, rTgt)
 	})
 	t.Run("existing database with blinded blocks type should error if user enables full blocks feature flag", func(t *testing.T) {
 		store := setupDB(t)

beacon-chain/db/kv/schema.go

@@ -61,8 +61,8 @@ var (
 
 	// block root included in the beacon state used by weak subjectivity initial sync
 	originCheckpointBlockRootKey = []byte("origin-checkpoint-block-root")
-	// block root tracking the progress of backfill, or pointing at genesis if backfill has not been initiated
-	backfillBlockRootKey = []byte("backfill-block-root")
+	// tracking data about an ongoing backfill
+	backfillStatusKey = []byte("backfill-status")
 
 	// Deprecated: This index key was migrated in PR 6461. Do not use, except for migrations.
 	lastArchivedIndexKey = []byte("last-archived")

beacon-chain/db/kv/wss.go

@@ -8,6 +8,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/config/params"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
 	"github.com/prysmaticlabs/prysm/v4/encoding/ssz/detect"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
 	ethpb "github.com/prysmaticlabs/prysm/v4/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/v4/runtime/version"
 )
@@ -17,18 +18,6 @@ import (
 // syncing, using the provided values as their point of origin. This is an alternative
 // to syncing from genesis, and should only be run on an empty database.
 func (s *Store) SaveOrigin(ctx context.Context, serState, serBlock []byte) error {
-	genesisRoot, err := s.GenesisBlockRoot(ctx)
-	if err != nil {
-		if errors.Is(err, ErrNotFoundGenesisBlockRoot) {
-			return errors.Wrap(err, "genesis block root not found: genesis must be provided for checkpoint sync")
-		}
-		return errors.Wrap(err, "genesis block root query error: checkpoint sync must verify genesis to proceed")
-	}
-	err = s.SaveBackfillBlockRoot(ctx, genesisRoot)
-	if err != nil {
-		return errors.Wrap(err, "unable to save genesis root as initial backfill starting point for checkpoint sync")
-	}
-
 	cf, err := detect.FromState(serState)
 	if err != nil {
 		return errors.Wrap(err, "could not sniff config+fork for origin state bytes")
@@ -50,11 +39,24 @@ func (s *Store) SaveOrigin(ctx context.Context, serState, serBlock []byte) error
 	}
 	blk := wblk.Block()
 
-	// save block
 	blockRoot, err := blk.HashTreeRoot()
 	if err != nil {
 		return errors.Wrap(err, "could not compute HashTreeRoot of checkpoint block")
 	}
+
+	pr := blk.ParentRoot()
+	bf := &dbval.BackfillStatus{
+		LowSlot:       uint64(wblk.Block().Slot()),
+		LowRoot:       blockRoot[:],
+		LowParentRoot: pr[:],
+		OriginRoot:    blockRoot[:],
+		OriginSlot:    uint64(wblk.Block().Slot()),
+	}
+
+	if err = s.SaveBackfillStatus(ctx, bf); err != nil {
+		return errors.Wrap(err, "unable to save backfill status data to db for checkpoint sync")
+	}
+
 	log.Infof("saving checkpoint block to db, w/ root=%#x", blockRoot)
 	if err := s.SaveBlock(ctx, wblk); err != nil {
 		return errors.Wrap(err, "could not save checkpoint block")

beacon-chain/node/BUILD.bazel

@@ -40,6 +40,7 @@ go_library(
         "//beacon-chain/operations/synccommittee:go_default_library",
         "//beacon-chain/operations/voluntaryexits:go_default_library",
         "//beacon-chain/p2p:go_default_library",
+        "//beacon-chain/p2p/peers:go_default_library",
         "//beacon-chain/rpc:go_default_library",
         "//beacon-chain/slasher:go_default_library",
         "//beacon-chain/startup:go_default_library",
@@ -47,6 +48,7 @@ go_library(
         "//beacon-chain/state/stategen:go_default_library",
         "//beacon-chain/sync:go_default_library",
         "//beacon-chain/sync/backfill:go_default_library",
+        "//beacon-chain/sync/backfill/coverage:go_default_library",
         "//beacon-chain/sync/checkpoint:go_default_library",
         "//beacon-chain/sync/genesis:go_default_library",
         "//beacon-chain/sync/initial-sync:go_default_library",

beacon-chain/node/node.go

@@ -42,6 +42,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/operations/synccommittee"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/operations/voluntaryexits"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p/peers"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/rpc"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/slasher"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
@@ -49,6 +50,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state/stategen"
 	regularsync "github.com/prysmaticlabs/prysm/v4/beacon-chain/sync"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill/coverage"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/checkpoint"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/genesis"
 	initialsync "github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/initial-sync"
@@ -113,6 +115,7 @@ type BeaconNode struct {
 	CheckpointInitializer   checkpoint.Initializer
 	forkChoicer             forkchoice.ForkChoicer
 	clockWaiter             startup.ClockWaiter
+	BackfillOpts            []backfill.ServiceOption
 	initialSyncComplete     chan struct{}
 	BlobStorage             *filesystem.BlobStorage
 	blobRetentionEpochs     primitives.Epoch
@@ -215,10 +218,23 @@ func New(cliCtx *cli.Context, cancel context.CancelFunc, opts ...Option) (*Beaco
 		return nil, err
 	}
 
-	bfs := backfill.NewStatus(beacon.db)
-	if err := bfs.Reload(ctx); err != nil {
+	log.Debugln("Registering P2P Service")
+	if err := beacon.registerP2P(cliCtx); err != nil {
+		return nil, err
+	}
+
+	bfs, err := backfill.NewUpdater(ctx, beacon.db)
+	if err != nil {
 		return nil, errors.Wrap(err, "backfill status initialization error")
 	}
+	pa := peers.NewAssigner(beacon.fetchP2P().Peers(), beacon.forkChoicer)
+	bf, err := backfill.NewService(ctx, bfs, beacon.clockWaiter, beacon.fetchP2P(), pa, beacon.BackfillOpts...)
+	if err != nil {
+		return nil, errors.Wrap(err, "error initializing backfill service")
+	}
+	if err := beacon.services.RegisterService(bf); err != nil {
+		return nil, errors.Wrap(err, "error registering backfill service")
+	}
 
 	log.Debugln("Starting State Gen")
 	if err := beacon.startStateGen(ctx, bfs, beacon.forkChoicer); err != nil {
@@ -233,11 +249,6 @@ func New(cliCtx *cli.Context, cancel context.CancelFunc, opts ...Option) (*Beaco
 	beacon.verifyInitWaiter = verification.NewInitializerWaiter(
 		beacon.clockWaiter, forkchoice.NewROForkChoice(beacon.forkChoicer), beacon.stateGen)
 
-	log.Debugln("Registering P2P Service")
-	if err := beacon.registerP2P(cliCtx); err != nil {
-		return nil, err
-	}
-
 	log.Debugln("Registering POW Chain Service")
 	if err := beacon.registerPOWChainService(); err != nil {
 		return nil, err
@@ -534,8 +545,8 @@ func (b *BeaconNode) startSlasherDB(cliCtx *cli.Context) error {
 	return nil
 }
 
-func (b *BeaconNode) startStateGen(ctx context.Context, bfs *backfill.Status, fc forkchoice.ForkChoicer) error {
-	opts := []stategen.Option{stategen.WithBackfillStatus(bfs)}
+func (b *BeaconNode) startStateGen(ctx context.Context, bfs coverage.AvailableBlocker, fc forkchoice.ForkChoicer) error {
+	opts := []stategen.Option{stategen.WithAvailableBlocker(bfs)}
 	sg := stategen.New(b.db, fc, opts...)
 
 	cp, err := b.db.FinalizedCheckpoint(ctx)

beacon-chain/p2p/peers/BUILD.bazel

@@ -3,6 +3,7 @@ load("@prysm//tools/go:def.bzl", "go_library", "go_test")
 go_library(
     name = "go_default_library",
     srcs = [
+        "assigner.go",
         "log.go",
         "status.go",
     ],
@@ -12,8 +13,10 @@ go_library(
         "//cmd:__subpackages__",
     ],
     deps = [
+        "//beacon-chain/forkchoice/types:go_default_library",
         "//beacon-chain/p2p/peers/peerdata:go_default_library",
         "//beacon-chain/p2p/peers/scorers:go_default_library",
+        "//cmd/beacon-chain/flags:go_default_library",
         "//config/features:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/primitives:go_default_library",
@@ -28,6 +31,7 @@ go_library(
         "@com_github_libp2p_go_libp2p//core/peer:go_default_library",
         "@com_github_multiformats_go_multiaddr//:go_default_library",
         "@com_github_multiformats_go_multiaddr//net:go_default_library",
+        "@com_github_pkg_errors//:go_default_library",
         "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
         "@com_github_sirupsen_logrus//:go_default_library",
     ],
@@ -36,6 +40,7 @@ go_library(
 go_test(
     name = "go_default_test",
     srcs = [
+        "assigner_test.go",
         "benchmark_test.go",
         "peers_test.go",
         "status_test.go",

beacon-chain/p2p/peers/assigner.go

@@ -0,0 +1,78 @@
+package peers
+
+import (
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/pkg/errors"
+	forkchoicetypes "github.com/prysmaticlabs/prysm/v4/beacon-chain/forkchoice/types"
+	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/flags"
+	"github.com/prysmaticlabs/prysm/v4/config/params"
+	"github.com/sirupsen/logrus"
+)
+
+// FinalizedCheckpointer describes the minimum capability that Assigner needs from forkchoice.
+// That is, the ability to retrieve the latest finalized checkpoint to help with peer evaluation.
+type FinalizedCheckpointer interface {
+	FinalizedCheckpoint() *forkchoicetypes.Checkpoint
+}
+
+// NewAssigner assists in the correct construction of an Assigner by code in other packages,
+// assuring all the important private member fields are given values.
+// The FinalizedCheckpointer is used to retrieve the latest finalized checkpoint each time peers are requested.
+// Peers that report an older finalized checkpoint are filtered out.
+func NewAssigner(s *Status, fc FinalizedCheckpointer) *Assigner {
+	return &Assigner{
+		ps: s,
+		fc: fc,
+	}
+}
+
+// Assigner uses the "BestFinalized" peer scoring method to pick the next-best peer to receive rpc requests.
+type Assigner struct {
+	ps *Status
+	fc FinalizedCheckpointer
+}
+
+// ErrInsufficientSuitable is a sentinel error, signaling that a peer couldn't be assigned because there are currently
+// not enough peers that match our selection criteria to serve rpc requests. It is the responsibility of the caller to
+// look for this error and continue to try calling Assign with appropriate backoff logic.
+var ErrInsufficientSuitable = errors.New("no suitable peers")
+
+func (a *Assigner) freshPeers() ([]peer.ID, error) {
+	required := params.BeaconConfig().MaxPeersToSync
+	if flags.Get().MinimumSyncPeers < required {
+		required = flags.Get().MinimumSyncPeers
+	}
+	_, peers := a.ps.BestFinalized(params.BeaconConfig().MaxPeersToSync, a.fc.FinalizedCheckpoint().Epoch)
+	if len(peers) < required {
+		log.WithFields(logrus.Fields{
+			"suitable": len(peers),
+			"required": required}).Warn("Unable to assign peer while suitable peers < required ")
+		return nil, ErrInsufficientSuitable
+	}
+	return peers, nil
+}
+
+// Assign uses the "BestFinalized" method to select the best peers that agree on a canonical block
+// for the configured finalized epoch. At most `n` peers will be returned. The `busy` param can be used
+// to filter out peers that we know we don't want to connect to, for instance if we are trying to limit
+// the number of outbound requests to each peer from a given component.
+func (a *Assigner) Assign(busy map[peer.ID]bool, n int) ([]peer.ID, error) {
+	best, err := a.freshPeers()
+	if err != nil {
+		return nil, err
+	}
+	return pickBest(busy, n, best), nil
+}
+
+func pickBest(busy map[peer.ID]bool, n int, best []peer.ID) []peer.ID {
+	ps := make([]peer.ID, 0, n)
+	for _, p := range best {
+		if len(ps) == n {
+			return ps
+		}
+		if !busy[p] {
+			ps = append(ps, p)
+		}
+	}
+	return ps
+}

beacon-chain/p2p/peers/assigner_test.go

@@ -0,0 +1,114 @@
+package peers
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+)
+
+func TestPickBest(t *testing.T) {
+	best := testPeerIds(10)
+	cases := []struct {
+		name     string
+		busy     map[peer.ID]bool
+		n        int
+		best     []peer.ID
+		expected []peer.ID
+	}{
+		{
+			name: "",
+			n:    0,
+		},
+		{
+			name:     "none busy",
+			n:        1,
+			expected: best[0:1],
+		},
+		{
+			name:     "all busy except last",
+			n:        1,
+			busy:     testBusyMap(best[0 : len(best)-1]),
+			expected: best[len(best)-1:],
+		},
+		{
+			name:     "all busy except i=5",
+			n:        1,
+			busy:     testBusyMap(append(append([]peer.ID{}, best[0:5]...), best[6:]...)),
+			expected: []peer.ID{best[5]},
+		},
+		{
+			name: "all busy - 0 results",
+			n:    1,
+			busy: testBusyMap(best),
+		},
+		{
+			name:     "first half busy",
+			n:        5,
+			busy:     testBusyMap(best[0:5]),
+			expected: best[5:],
+		},
+		{
+			name:     "back half busy",
+			n:        5,
+			busy:     testBusyMap(best[5:]),
+			expected: best[0:5],
+		},
+		{
+			name:     "pick all ",
+			n:        10,
+			expected: best,
+		},
+		{
+			name: "none available",
+			n:    10,
+			best: []peer.ID{},
+		},
+		{
+			name:     "not enough",
+			n:        10,
+			best:     best[0:1],
+			expected: best[0:1],
+		},
+		{
+			name:     "not enough, some busy",
+			n:        10,
+			best:     best[0:6],
+			busy:     testBusyMap(best[0:5]),
+			expected: best[5:6],
+		},
+	}
+	for _, c := range cases {
+		name := fmt.Sprintf("n=%d", c.n)
+		if c.name != "" {
+			name += " " + c.name
+		}
+		t.Run(name, func(t *testing.T) {
+			if c.best == nil {
+				c.best = best
+			}
+			pb := pickBest(c.busy, c.n, c.best)
+			require.Equal(t, len(c.expected), len(pb))
+			for i := range c.expected {
+				require.Equal(t, c.expected[i], pb[i])
+			}
+		})
+	}
+}
+
+func testBusyMap(b []peer.ID) map[peer.ID]bool {
+	m := make(map[peer.ID]bool)
+	for i := range b {
+		m[b[i]] = true
+	}
+	return m
+}
+
+func testPeerIds(n int) []peer.ID {
+	pids := make([]peer.ID, n)
+	for i := range pids {
+		pids[i] = peer.ID(fmt.Sprintf("%d", i))
+	}
+	return pids
+}

beacon-chain/state/interfaces.go

@@ -121,6 +121,7 @@ type ReadOnlyValidators interface {
 	ValidatorAtIndex(idx primitives.ValidatorIndex) (*ethpb.Validator, error)
 	ValidatorAtIndexReadOnly(idx primitives.ValidatorIndex) (ReadOnlyValidator, error)
 	ValidatorIndexByPubkey(key [fieldparams.BLSPubkeyLength]byte) (primitives.ValidatorIndex, bool)
+	PublicKeys() ([][fieldparams.BLSPubkeyLength]byte, error)
 	PubkeyAtIndex(idx primitives.ValidatorIndex) [fieldparams.BLSPubkeyLength]byte
 	NumValidators() int
 	ReadFromEveryValidator(f func(idx int, val ReadOnlyValidator) error) error

beacon-chain/state/state-native/getters_validator.go

@@ -181,6 +181,27 @@ func (b *BeaconState) PubkeyAtIndex(idx primitives.ValidatorIndex) [fieldparams.
 	return bytesutil.ToBytes48(v.PublicKey)
 }
 
+// PublicKeys builds a list of all validator public keys, with each key's index aligned to its validator index.
+func (b *BeaconState) PublicKeys() ([][fieldparams.BLSPubkeyLength]byte, error) {
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	l := b.validatorsLen()
+	res := make([][fieldparams.BLSPubkeyLength]byte, l)
+	for i := 0; i < l; i++ {
+		if features.Get().EnableExperimentalState {
+			val, err := b.validatorsMultiValue.At(b, uint64(i))
+			if err != nil {
+				return nil, err
+			}
+			copy(res[i][:], val.PublicKey)
+		} else {
+			copy(res[i][:], b.validators[i].PublicKey)
+		}
+	}
+	return res, nil
+}
+
 // NumValidators returns the size of the validator registry.
 func (b *BeaconState) NumValidators() int {
 	b.lock.RLock()

beacon-chain/state/stategen/BUILD.bazel

@@ -31,7 +31,7 @@ go_library(
         "//beacon-chain/db/filters:go_default_library",
         "//beacon-chain/forkchoice:go_default_library",
         "//beacon-chain/state:go_default_library",
-        "//beacon-chain/sync/backfill:go_default_library",
+        "//beacon-chain/sync/backfill/coverage:go_default_library",
         "//cache/lru:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/blocks:go_default_library",

beacon-chain/state/stategen/getter.go

@@ -332,9 +332,8 @@ func (s *State) CombinedCache() *CombinedCache {
 }
 
 func (s *State) slotAvailable(slot primitives.Slot) bool {
-	// default to assuming node was initialized from genesis - backfill only needs to be specified for checkpoint sync
-	if s.backfillStatus == nil {
+	if s.avb == nil {
 		return true
 	}
-	return s.backfillStatus.SlotCovered(slot)
+	return s.avb.AvailableBlock(slot)
 }

beacon-chain/state/stategen/service.go

@@ -13,7 +13,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/forkchoice"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
-	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill/coverage"
 	"github.com/prysmaticlabs/prysm/v4/config/params"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
 	"github.com/prysmaticlabs/prysm/v4/crypto/bls"
@@ -51,7 +51,7 @@ type State struct {
 	finalizedInfo           *finalizedInfo
 	epochBoundaryStateCache *epochBoundaryState
 	saveHotStateDB          *saveHotStateDbConfig
-	backfillStatus          *backfill.Status
+	avb                     coverage.AvailableBlocker
 	migrationLock           *sync.Mutex
 	fc                      forkchoice.ForkChoicer
 }
@@ -78,9 +78,11 @@ type finalizedInfo struct {
 // Option is a functional option for controlling the initialization of a *State value
 type Option func(*State)
 
-func WithBackfillStatus(bfs *backfill.Status) Option {
+// WithAvailableBlocker gives stategen an AvailableBlocker, which is used to determine if a given
+// block is available. This is necessary because backfill creates a hole in the block history.
+func WithAvailableBlocker(avb coverage.AvailableBlocker) Option {
 	return func(sg *State) {
-		sg.backfillStatus = bfs
+		sg.avb = avb
 	}
 }
 

beacon-chain/sync/backfill/BUILD.bazel

@@ -2,30 +2,78 @@ load("@prysm//tools/go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
-    srcs = ["status.go"],
+    srcs = [
+        "batch.go",
+        "batcher.go",
+        "metrics.go",
+        "pool.go",
+        "service.go",
+        "status.go",
+        "verify.go",
+        "worker.go",
+    ],
     importpath = "github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill",
     visibility = ["//visibility:public"],
     deps = [
+        "//beacon-chain/core/helpers:go_default_library",
+        "//beacon-chain/core/signing:go_default_library",
         "//beacon-chain/db:go_default_library",
+        "//beacon-chain/p2p:go_default_library",
+        "//beacon-chain/p2p/peers:go_default_library",
+        "//beacon-chain/startup:go_default_library",
+        "//beacon-chain/state:go_default_library",
+        "//beacon-chain/sync:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//config/params:go_default_library",
         "//consensus-types/blocks:go_default_library",
         "//consensus-types/interfaces:go_default_library",
         "//consensus-types/primitives:go_default_library",
+        "//crypto/bls:go_default_library",
+        "//encoding/bytesutil:go_default_library",
+        "//network/forks:go_default_library",
+        "//proto/dbval:go_default_library",
+        "//proto/prysm/v1alpha1:go_default_library",
+        "//runtime:go_default_library",
+        "//time/slots:go_default_library",
+        "@com_github_libp2p_go_libp2p//core/peer:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
+        "@com_github_prometheus_client_golang//prometheus:go_default_library",
+        "@com_github_prometheus_client_golang//prometheus/promauto:go_default_library",
+        "@com_github_sirupsen_logrus//:go_default_library",
     ],
 )
 
 go_test(
     name = "go_default_test",
-    srcs = ["status_test.go"],
+    srcs = [
+        "batcher_test.go",
+        "pool_test.go",
+        "service_test.go",
+        "status_test.go",
+        "verify_test.go",
+    ],
     embed = [":go_default_library"],
     deps = [
+        "//beacon-chain/core/signing:go_default_library",
+        "//beacon-chain/db:go_default_library",
+        "//beacon-chain/p2p/testing:go_default_library",
+        "//beacon-chain/startup:go_default_library",
+        "//beacon-chain/state:go_default_library",
+        "//config/fieldparams:go_default_library",
         "//config/params:go_default_library",
         "//consensus-types/blocks:go_default_library",
         "//consensus-types/blocks/testing:go_default_library",
         "//consensus-types/interfaces:go_default_library",
         "//consensus-types/primitives:go_default_library",
+        "//crypto/bls:go_default_library",
+        "//encoding/bytesutil:go_default_library",
+        "//network/forks:go_default_library",
+        "//proto/dbval:go_default_library",
+        "//runtime/interop:go_default_library",
         "//testing/require:go_default_library",
         "//testing/util:go_default_library",
+        "@com_github_ethereum_go_ethereum//common/hexutil:go_default_library",
+        "@com_github_libp2p_go_libp2p//core/peer:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
     ],
 )

beacon-chain/sync/backfill/batch.go

@@ -0,0 +1,141 @@
+package backfill
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	eth "github.com/prysmaticlabs/prysm/v4/proto/prysm/v1alpha1"
+	log "github.com/sirupsen/logrus"
+)
+
+// ErrChainBroken indicates a backfill batch can't be imported to the db because it is not known to be the ancestor
+// of the canonical chain.
+var ErrChainBroken = errors.New("batch is not the ancestor of a known finalized root")
+
+type batchState int
+
+func (s batchState) String() string {
+	switch s {
+	case batchNil:
+		return "nil"
+	case batchInit:
+		return "init"
+	case batchSequenced:
+		return "sequenced"
+	case batchErrRetryable:
+		return "error_retryable"
+	case batchImportable:
+		return "importable"
+	case batchImportComplete:
+		return "import_complete"
+	case batchEndSequence:
+		return "end_sequence"
+	default:
+		return "unknown"
+	}
+}
+
+const (
+	batchNil batchState = iota
+	batchInit
+	batchSequenced
+	batchErrRetryable
+	batchImportable
+	batchImportComplete
+	batchEndSequence
+)
+
+type batchId string
+
+type batch struct {
+	firstScheduled time.Time
+	scheduled      time.Time
+	seq            int // sequence identifier, ie how many times has the sequence() method served this batch
+	retries        int
+	begin          primitives.Slot
+	end            primitives.Slot // half-open interval, [begin, end), ie >= start, < end.
+	results        VerifiedROBlocks
+	err            error
+	state          batchState
+	pid            peer.ID
+}
+
+func (b batch) logFields() log.Fields {
+	return map[string]interface{}{
+		"batch_id":  b.id(),
+		"state":     b.state.String(),
+		"scheduled": b.scheduled.String(),
+		"seq":       b.seq,
+		"retries":   b.retries,
+		"begin":     b.begin,
+		"end":       b.end,
+		"pid":       b.pid,
+	}
+}
+
+func (b batch) replaces(r batch) bool {
+	if r.state == batchImportComplete {
+		return false
+	}
+	if b.begin != r.begin {
+		return false
+	}
+	if b.end != r.end {
+		return false
+	}
+	return b.seq >= r.seq
+}
+
+func (b batch) id() batchId {
+	return batchId(fmt.Sprintf("%d:%d", b.begin, b.end))
+}
+
+func (b batch) ensureParent(expected [32]byte) error {
+	tail := b.results[len(b.results)-1]
+	if tail.Root() != expected {
+		return errors.Wrapf(ErrChainBroken, "last parent_root=%#x, tail root=%#x", expected, tail.Root())
+	}
+	return nil
+}
+
+func (b batch) request() *eth.BeaconBlocksByRangeRequest {
+	return &eth.BeaconBlocksByRangeRequest{
+		StartSlot: b.begin,
+		Count:     uint64(b.end - b.begin),
+		Step:      1,
+	}
+}
+
+func (b batch) withState(s batchState) batch {
+	if s == batchSequenced {
+		b.scheduled = time.Now()
+		switch b.state {
+		case batchErrRetryable:
+			b.retries += 1
+			log.WithFields(b.logFields()).Info("sequencing batch for retry")
+		case batchInit, batchNil:
+			b.firstScheduled = b.scheduled
+		}
+	}
+	if s == batchImportComplete {
+		backfillBatchTimeRoundtrip.Observe(float64(time.Since(b.firstScheduled).Milliseconds()))
+		log.WithFields(b.logFields()).Debug("Backfill batch imported.")
+	}
+	b.state = s
+	b.seq += 1
+	return b
+}
+
+func (b batch) withPeer(p peer.ID) batch {
+	b.pid = p
+	backfillBatchTimeWaiting.Observe(float64(time.Since(b.scheduled).Milliseconds()))
+	return b
+}
+
+func (b batch) withRetryableError(err error) batch {
+	b.err = err
+	return b.withState(batchErrRetryable)
+}

beacon-chain/sync/backfill/batcher.go

@@ -0,0 +1,197 @@
+package backfill
+
+import (
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+)
+
+var errMaxBatches = errors.New("backfill batch requested in excess of max outstanding batches")
+var errEndSequence = errors.New("sequence has terminated, no more backfill batches will be produced")
+var errCannotDecreaseMinimum = errors.New("the minimum backfill slot can only be increased, not decreased")
+
+type batchSequencer struct {
+	batcher batcher
+	seq     []batch
+}
+
+// sequence() is meant as a verb "arrange in a particular order".
+// sequence determines the next set of batches that should be worked on based on the state of the batches
+// in its internal view. sequence relies on update() for updates to its view of the
+// batches it has previously sequenced.
+func (c *batchSequencer) sequence() ([]batch, error) {
+	s := make([]batch, 0)
+	// batch start slots are in descending order, c.seq[n].begin == c.seq[n+1].end
+	for i := range c.seq {
+		switch c.seq[i].state {
+		case batchInit, batchErrRetryable:
+			c.seq[i] = c.seq[i].withState(batchSequenced)
+			s = append(s, c.seq[i])
+		case batchNil:
+			// batchNil is the zero value of the batch type.
+			// This case means that we are initializing a batch that was created by the
+			// initial allocation of the seq slice, so batcher need to compute its bounds.
+			var b batch
+			if i == 0 {
+				// The first item in the list is a special case, subsequent items are initialized
+				// relative to the preceding batches.
+				b = c.batcher.before(c.batcher.max)
+			} else {
+				b = c.batcher.beforeBatch(c.seq[i-1])
+			}
+			c.seq[i] = b.withState(batchSequenced)
+			s = append(s, c.seq[i])
+		case batchEndSequence:
+			if len(s) == 0 {
+				s = append(s, c.seq[i])
+			}
+		default:
+			continue
+		}
+	}
+	if len(s) == 0 {
+		return nil, errMaxBatches
+	}
+
+	return s, nil
+}
+
+// update serves 2 roles.
+//   - updating batchSequencer's copy of the given batch.
+//   - removing batches that are completely imported from the sequence,
+//     so that they are not returned the next time import() is called, and populating
+//     seq with new batches that are ready to be worked on.
+func (c *batchSequencer) update(b batch) {
+	done := 0
+	for i := 0; i < len(c.seq); i++ {
+		if b.replaces(c.seq[i]) {
+			c.seq[i] = b
+		}
+		// Assumes invariant that batches complete and update is called in order.
+		// This should be true because the code using the sequencer doesn't know the expected parent
+		// for a batch until it imports the previous batch.
+		if c.seq[i].state == batchImportComplete {
+			done += 1
+			continue
+		}
+		// Move the unfinished batches to overwrite the finished ones.
+		// eg consider [a,b,c,d,e] where a,b are done
+		// when i==2, done==2 (since done was incremented for a and b)
+		// so we want to copy c to a, then on i=3, d to b, then on i=4 e to c.
+		c.seq[i-done] = c.seq[i]
+	}
+	// Overwrite the moved batches with the next ones in the sequence.
+	// Continuing the example in the comment above, len(c.seq)==5, done=2, so i=3.
+	// We want to replace index 3 with the batch that should be processed after index 2,
+	// which was previously the earliest known batch, and index 4 with the batch that should
+	// be processed after index 3, the new earliest batch.
+	for i := len(c.seq) - done; i < len(c.seq); i++ {
+		c.seq[i] = c.batcher.beforeBatch(c.seq[i-1])
+	}
+}
+
+// importable returns all batches that are ready to be imported. This means they satisfy 2 conditions:
+//   - They are in state batchImportable, which means their data has been downloaded and proposer signatures have been verified.
+//   - There are no batches that are not in state batchImportable between them and the start of the slice. This ensures that they
+//     can be connected to the canonical chain, either because the root of the last block in the batch matches the parent_root of
+//     the oldest block in the canonical chain, or because the root of the last block in the batch matches the parent_root of the
+//     new block preceding them in the slice (which must connect to the batch before it, or to the canonical chain if it is first).
+func (c *batchSequencer) importable() []batch {
+	imp := make([]batch, 0)
+	for i := range c.seq {
+		if c.seq[i].state == batchImportable {
+			imp = append(imp, c.seq[i])
+			continue
+		}
+		// as soon as we hit a batch with a different state, we return everything leading to it.
+		// If the first element isn't importable, we'll return an empty slice.
+		break
+	}
+	return imp
+}
+
+// moveMinimum enables the backfill service to change the slot where the batcher will start replying with
+// batch state batchEndSequence (signaling that no new batches will be produced). This is done in response to
+// epochs advancing, which shrinks the gap between <checkpoint slot> and <current slot>-MIN_EPOCHS_FOR_BLOCK_REQUESTS,
+// allowing the node to download a smaller number of blocks.
+func (c *batchSequencer) moveMinimum(min primitives.Slot) error {
+	if min < c.batcher.min {
+		return errCannotDecreaseMinimum
+	}
+	c.batcher.min = min
+	return nil
+}
+
+// countWithState provides a view into how many batches are in a particular state
+// to be used for logging or metrics purposes.
+func (c *batchSequencer) countWithState(s batchState) int {
+	n := 0
+	for i := 0; i < len(c.seq); i++ {
+		if c.seq[i].state == s {
+			n += 1
+		}
+	}
+	return n
+}
+
+// numTodo computes the number of remaining batches for metrics and logging purposes.
+func (c *batchSequencer) numTodo() int {
+	if len(c.seq) == 0 {
+		return 0
+	}
+	lowest := c.seq[len(c.seq)-1]
+	todo := 0
+	if lowest.state != batchEndSequence {
+		todo = c.batcher.remaining(lowest.begin)
+	}
+	for _, b := range c.seq {
+		switch b.state {
+		case batchEndSequence, batchImportComplete, batchNil:
+			continue
+		default:
+			todo += 1
+		}
+	}
+	return todo
+}
+
+func newBatchSequencer(seqLen int, min, max, size primitives.Slot) *batchSequencer {
+	b := batcher{min: min, max: max, size: size}
+	seq := make([]batch, seqLen)
+	return &batchSequencer{batcher: b, seq: seq}
+}
+
+type batcher struct {
+	min  primitives.Slot
+	max  primitives.Slot
+	size primitives.Slot
+}
+
+func (r batcher) remaining(upTo primitives.Slot) int {
+	if r.min >= upTo {
+		return 0
+	}
+	delta := upTo - r.min
+	if delta%r.size != 0 {
+		return int(delta/r.size) + 1
+	}
+	return int(delta / r.size)
+}
+
+func (r batcher) beforeBatch(upTo batch) batch {
+	return r.before(upTo.begin)
+}
+
+func (r batcher) before(upTo primitives.Slot) batch {
+	// upTo is an exclusive upper bound. Requesting a batch before the lower bound of backfill signals the end of the
+	// backfill process.
+	if upTo <= r.min {
+		return batch{begin: upTo, end: upTo, state: batchEndSequence}
+	}
+	begin := r.min
+	if upTo > r.size+r.min {
+		begin = upTo - r.size
+	}
+
+	// batch.end is exclusive, .begin is inclusive, so the prev.end = next.begin
+	return batch{begin: begin, end: upTo, state: batchInit}
+}

beacon-chain/sync/backfill/batcher_test.go

@@ -0,0 +1,208 @@
+package backfill
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+)
+
+func TestBatcherBefore(t *testing.T) {
+	cases := []struct {
+		name   string
+		b      batcher
+		upTo   []primitives.Slot
+		expect []batch
+	}{
+		{
+			name: "size 10",
+			b:    batcher{min: 0, size: 10},
+			upTo: []primitives.Slot{33, 30, 10, 6},
+			expect: []batch{
+				{begin: 23, end: 33, state: batchInit},
+				{begin: 20, end: 30, state: batchInit},
+				{begin: 0, end: 10, state: batchInit},
+				{begin: 0, end: 6, state: batchInit},
+			},
+		},
+		{
+			name: "size 4",
+			b:    batcher{min: 0, size: 4},
+			upTo: []primitives.Slot{33, 6, 4},
+			expect: []batch{
+				{begin: 29, end: 33, state: batchInit},
+				{begin: 2, end: 6, state: batchInit},
+				{begin: 0, end: 4, state: batchInit},
+			},
+		},
+		{
+			name: "trigger end",
+			b:    batcher{min: 20, size: 10},
+			upTo: []primitives.Slot{33, 30, 25, 21, 20, 19},
+			expect: []batch{
+				{begin: 23, end: 33, state: batchInit},
+				{begin: 20, end: 30, state: batchInit},
+				{begin: 20, end: 25, state: batchInit},
+				{begin: 20, end: 21, state: batchInit},
+				{begin: 20, end: 20, state: batchEndSequence},
+				{begin: 19, end: 19, state: batchEndSequence},
+			},
+		},
+	}
+	for _, c := range cases {
+		for i := range c.upTo {
+			upTo := c.upTo[i]
+			expect := c.expect[i]
+			t.Run(fmt.Sprintf("%s upTo %d", c.name, upTo), func(t *testing.T) {
+				got := c.b.before(upTo)
+				require.Equal(t, expect.begin, got.begin)
+				require.Equal(t, expect.end, got.end)
+				require.Equal(t, expect.state, got.state)
+			})
+		}
+	}
+}
+
+func TestBatchSequencer(t *testing.T) {
+	var min, max, size primitives.Slot
+	seqLen := 8
+	min = 0
+	max = 11235
+	size = 64
+	seq := newBatchSequencer(seqLen, min, max, size)
+	expected := []batch{
+		{begin: 11171, end: 11235},
+		{begin: 11107, end: 11171},
+		{begin: 11043, end: 11107},
+		{begin: 10979, end: 11043},
+		{begin: 10915, end: 10979},
+		{begin: 10851, end: 10915},
+		{begin: 10787, end: 10851},
+		{begin: 10723, end: 10787},
+	}
+	got, err := seq.sequence()
+	require.Equal(t, seqLen, len(got))
+	for i := 0; i < seqLen; i++ {
+		g := got[i]
+		exp := expected[i]
+		require.NoError(t, err)
+		require.Equal(t, exp.begin, g.begin)
+		require.Equal(t, exp.end, g.end)
+		require.Equal(t, batchSequenced, g.state)
+	}
+	// This should give us the error indicating there are too many outstanding batches.
+	_, err = seq.sequence()
+	require.ErrorIs(t, err, errMaxBatches)
+
+	// mark the last batch completed so we can call sequence again.
+	last := seq.seq[len(seq.seq)-1]
+	// With this state, the batch should get served back to us as the next batch.
+	last.state = batchErrRetryable
+	seq.update(last)
+	nextS, err := seq.sequence()
+	require.Equal(t, 1, len(nextS))
+	next := nextS[0]
+	require.NoError(t, err)
+	require.Equal(t, last.begin, next.begin)
+	require.Equal(t, last.end, next.end)
+	// sequence() should replace the batchErrRetryable state with batchSequenced.
+	require.Equal(t, batchSequenced, next.state)
+
+	// No batches have been marked importable.
+	require.Equal(t, 0, len(seq.importable()))
+
+	// Mark our batch importable and make sure it shows up in the list of importable batches.
+	next.state = batchImportable
+	seq.update(next)
+	require.Equal(t, 0, len(seq.importable()))
+	first := seq.seq[0]
+	first.state = batchImportable
+	seq.update(first)
+	require.Equal(t, 1, len(seq.importable()))
+	require.Equal(t, len(seq.seq), seqLen)
+	// change the last element back to batchInit so that the importable test stays simple
+	last = seq.seq[len(seq.seq)-1]
+	last.state = batchInit
+	seq.update(last)
+	// ensure that the number of importable elements grows as the list is marked importable
+	for i := 0; i < len(seq.seq); i++ {
+		seq.seq[i].state = batchImportable
+		require.Equal(t, i+1, len(seq.importable()))
+	}
+	// reset everything to init
+	for i := 0; i < len(seq.seq); i++ {
+		seq.seq[i].state = batchInit
+		require.Equal(t, 0, len(seq.importable()))
+	}
+	// loop backwards and make sure importable is zero until the first element is importable
+	for i := len(seq.seq) - 1; i > 0; i-- {
+		seq.seq[i].state = batchImportable
+		require.Equal(t, 0, len(seq.importable()))
+	}
+	seq.seq[0].state = batchImportable
+	require.Equal(t, len(seq.seq), len(seq.importable()))
+
+	// reset everything to init again
+	for i := 0; i < len(seq.seq); i++ {
+		seq.seq[i].state = batchInit
+		require.Equal(t, 0, len(seq.importable()))
+	}
+	// set first 3 elements to importable. we should see them in the result for importable()
+	// and be able to use update to cycle them away.
+	seq.seq[0].state, seq.seq[1].state, seq.seq[2].state = batchImportable, batchImportable, batchImportable
+	require.Equal(t, 3, len(seq.importable()))
+	a, b, c, z := seq.seq[0], seq.seq[1], seq.seq[2], seq.seq[3]
+	require.NotEqual(t, z.begin, seq.seq[2].begin)
+	require.NotEqual(t, z.begin, seq.seq[1].begin)
+	require.NotEqual(t, z.begin, seq.seq[0].begin)
+	a.state, b.state, c.state = batchImportComplete, batchImportComplete, batchImportComplete
+	seq.update(a)
+
+	// follow z as it moves down  the chain to the first spot
+	require.Equal(t, z.begin, seq.seq[2].begin)
+	require.NotEqual(t, z.begin, seq.seq[1].begin)
+	require.NotEqual(t, z.begin, seq.seq[0].begin)
+	seq.update(b)
+	require.NotEqual(t, z.begin, seq.seq[2].begin)
+	require.Equal(t, z.begin, seq.seq[1].begin)
+	require.NotEqual(t, z.begin, seq.seq[0].begin)
+	seq.update(c)
+	require.NotEqual(t, z.begin, seq.seq[2].begin)
+	require.NotEqual(t, z.begin, seq.seq[1].begin)
+	require.Equal(t, z.begin, seq.seq[0].begin)
+
+	// Check integrity of begin/end alignment across the sequence.
+	// Also update all the states to sequenced for the convenience of the next test.
+	for i := 1; i < len(seq.seq); i++ {
+		require.Equal(t, seq.seq[i].end, seq.seq[i-1].begin)
+		// won't touch the first element, which is fine because it is marked complete below.
+		seq.seq[i].state = batchSequenced
+	}
+
+	// set the min for the batcher close to the lowest slot. This will force the next batch to be partial and the batch
+	// after that to be the final batch.
+	newMin := seq.seq[len(seq.seq)-1].begin - 30
+	seq.batcher.min = newMin
+	first = seq.seq[0]
+	first.state = batchImportComplete
+	// update() with a complete state will cause the sequence to be extended with an additional batch
+	seq.update(first)
+	lastS, err := seq.sequence()
+	last = lastS[0]
+	require.NoError(t, err)
+	require.Equal(t, newMin, last.begin)
+	require.Equal(t, seq.seq[len(seq.seq)-2].begin, last.end)
+
+	// Mark first batch done again, this time check that sequence() gives errEndSequence.
+	first = seq.seq[0]
+	first.state = batchImportComplete
+	// update() with a complete state will cause the sequence to be extended with an additional batch
+	seq.update(first)
+	endExp, err := seq.sequence()
+	require.NoError(t, err)
+	require.Equal(t, 1, len(endExp))
+	end := endExp[0]
+	//require.ErrorIs(t, err, errEndSequence)
+	require.Equal(t, batchEndSequence, end.state)
+}

beacon-chain/sync/backfill/coverage/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["coverage.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill/coverage",
+    visibility = ["//visibility:public"],
+    deps = ["//consensus-types/primitives:go_default_library"],
+)

beacon-chain/sync/backfill/coverage/coverage.go

@@ -0,0 +1,9 @@
+package coverage
+
+import "github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+
+// AvailableBlocker can be used to check whether there is a finalized block in the db for the given slot.
+// This interface is typically fulfilled by backfill.Store.
+type AvailableBlocker interface {
+	AvailableBlock(primitives.Slot) bool
+}

beacon-chain/sync/backfill/metrics.go

@@ -0,0 +1,67 @@
+package backfill
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	oldestBatch = promauto.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "backfill_earliest_wip_slot",
+			Help: "Earliest slot that has been assigned to a worker.",
+		},
+	)
+	batchesWaiting = promauto.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "backfill_importable_batches_waiting",
+			Help: "Number of batches that are ready to be imported once they can be connected to the existing chain.",
+		},
+	)
+	backfillRemainingBatches = promauto.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "backfill_remaining_batches",
+			Help: "Backfill remaining batches.",
+		},
+	)
+	backfillBatchesImported = promauto.NewCounter(
+		prometheus.CounterOpts{
+			Name: "backfill_batches_imported",
+			Help: "Number of backfill batches downloaded and imported.",
+		},
+	)
+	backfillBatchApproximateBytes = promauto.NewCounter(
+		prometheus.CounterOpts{
+			Name: "backfill_batch_bytes_downloaded",
+			Help: "Count of bytes downloaded from peers",
+		},
+	)
+	backfillBatchTimeRoundtrip = promauto.NewHistogram(
+		prometheus.HistogramOpts{
+			Name:    "backfill_batch_time_roundtrip",
+			Help:    "Total time to import batch, from first scheduled to imported.",
+			Buckets: []float64{400, 800, 1600, 3200, 6400, 12800},
+		},
+	)
+	backfillBatchTimeWaiting = promauto.NewHistogram(
+		prometheus.HistogramOpts{
+			Name:    "backfill_batch_time_waiting",
+			Help:    "Time batch waited for a suitable peer.",
+			Buckets: []float64{50, 100, 300, 1000, 2000},
+		},
+	)
+	backfillBatchTimeDownloading = promauto.NewHistogram(
+		prometheus.HistogramOpts{
+			Name:    "backfill_batch_time_download",
+			Help:    "Time batch spent downloading blocks from peer.",
+			Buckets: []float64{100, 300, 1000, 2000, 4000, 8000},
+		},
+	)
+	backfillBatchTimeVerifying = promauto.NewHistogram(
+		prometheus.HistogramOpts{
+			Name:    "backfill_batch_time_verify",
+			Help:    "Time batch spent downloading blocks from peer.",
+			Buckets: []float64{100, 300, 1000, 2000, 4000, 8000},
+		},
+	)
+)

beacon-chain/sync/backfill/pool.go

@@ -0,0 +1,152 @@
+package backfill
+
+import (
+	"context"
+	"math"
+	"time"
+
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p/peers"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	log "github.com/sirupsen/logrus"
+)
+
+type batchWorkerPool interface {
+	spawn(ctx context.Context, n int, clock *startup.Clock, a PeerAssigner, v *verifier)
+	todo(b batch)
+	complete() (batch, error)
+}
+
+type worker interface {
+	run(context.Context)
+}
+
+type newWorker func(id workerId, in, out chan batch, c *startup.Clock, v *verifier) worker
+
+func defaultNewWorker(p p2p.P2P) newWorker {
+	return func(id workerId, in, out chan batch, c *startup.Clock, v *verifier) worker {
+		return newP2pWorker(id, p, in, out, c, v)
+	}
+}
+
+type p2pBatchWorkerPool struct {
+	maxBatches  int
+	newWorker   newWorker
+	toWorkers   chan batch
+	fromWorkers chan batch
+	toRouter    chan batch
+	fromRouter  chan batch
+	shutdownErr chan error
+	endSeq      []batch
+	ctx         context.Context
+	cancel      func()
+}
+
+var _ batchWorkerPool = &p2pBatchWorkerPool{}
+
+func newP2PBatchWorkerPool(p p2p.P2P, maxBatches int) *p2pBatchWorkerPool {
+	nw := defaultNewWorker(p)
+	return &p2pBatchWorkerPool{
+		newWorker:   nw,
+		toRouter:    make(chan batch, maxBatches),
+		fromRouter:  make(chan batch, maxBatches),
+		toWorkers:   make(chan batch),
+		fromWorkers: make(chan batch),
+		maxBatches:  maxBatches,
+		shutdownErr: make(chan error),
+	}
+}
+
+func (p *p2pBatchWorkerPool) spawn(ctx context.Context, n int, c *startup.Clock, a PeerAssigner, v *verifier) {
+	p.ctx, p.cancel = context.WithCancel(ctx)
+	go p.batchRouter(a)
+	for i := 0; i < n; i++ {
+		go p.newWorker(workerId(i), p.toWorkers, p.fromWorkers, c, v).run(p.ctx)
+	}
+}
+
+func (p *p2pBatchWorkerPool) todo(b batch) {
+	// Intercept batchEndSequence batches so workers can remain unaware of this state.
+	// Workers don't know what to do with batchEndSequence batches. They are a signal to the pool that the batcher
+	// has stopped producing things for the workers to do and the pool is close to winding down. See complete()
+	// to understand how the pool manages the state where all workers are idle
+	// and all incoming batches signal end of sequence.
+	if b.state == batchEndSequence {
+		p.endSeq = append(p.endSeq, b)
+		return
+	}
+	p.toRouter <- b
+}
+
+func (p *p2pBatchWorkerPool) complete() (batch, error) {
+	if len(p.endSeq) == p.maxBatches {
+		return p.endSeq[0], errEndSequence
+	}
+
+	select {
+	case b := <-p.fromRouter:
+		return b, nil
+	case err := <-p.shutdownErr:
+		return batch{}, errors.Wrap(err, "fatal error from backfill worker pool")
+	case <-p.ctx.Done():
+		log.WithError(p.ctx.Err()).Info("p2pBatchWorkerPool context canceled, shutting down")
+		return batch{}, p.ctx.Err()
+	}
+}
+
+func (p *p2pBatchWorkerPool) batchRouter(pa PeerAssigner) {
+	busy := make(map[peer.ID]bool)
+	todo := make([]batch, 0)
+	rt := time.NewTicker(time.Second)
+	earliest := primitives.Slot(math.MaxUint64)
+	for {
+		select {
+		case b := <-p.toRouter:
+			todo = append(todo, b)
+		case <-rt.C:
+			// Worker assignments can fail if assignBatch can't find a suitable peer.
+			// This ticker exists to periodically break out of the channel select
+			// to retry failed assignments.
+		case b := <-p.fromWorkers:
+			pid := b.pid
+			busy[pid] = false
+			p.fromRouter <- b
+		case <-p.ctx.Done():
+			log.WithError(p.ctx.Err()).Info("p2pBatchWorkerPool context canceled, shutting down")
+			p.shutdown(p.ctx.Err())
+			return
+		}
+		if len(todo) == 0 {
+			continue
+		}
+		// Try to assign as many outstanding batches as possible to peers and feed the assigned batches to workers.
+		assigned, err := pa.Assign(busy, len(todo))
+		if err != nil {
+			if errors.Is(err, peers.ErrInsufficientSuitable) {
+				// Transient error resulting from insufficient number of connected peers. Leave batches in
+				// queue and get to them whenever the peer situation is resolved.
+				continue
+			}
+			p.shutdown(err)
+			return
+		}
+		for _, pid := range assigned {
+			busy[pid] = true
+			todo[0].pid = pid
+			p.toWorkers <- todo[0].withPeer(pid)
+			if todo[0].begin < earliest {
+				earliest = todo[0].begin
+				oldestBatch.Set(float64(earliest))
+			}
+			todo = todo[1:]
+		}
+	}
+}
+
+func (p *p2pBatchWorkerPool) shutdown(err error) {
+	p.cancel()
+	p.shutdownErr <- err
+}

beacon-chain/sync/backfill/pool_test.go

@@ -0,0 +1,78 @@
+package backfill
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/libp2p/go-libp2p/core/peer"
+	p2ptest "github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p/testing"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+	"github.com/prysmaticlabs/prysm/v4/testing/util"
+)
+
+type mockAssigner struct {
+	err    error
+	assign []peer.ID
+}
+
+// Assign satisfies the PeerAssigner interface so that mockAssigner can be used in tests
+// in place of the concrete p2p implementation of PeerAssigner.
+func (m mockAssigner) Assign(busy map[peer.ID]bool, n int) ([]peer.ID, error) {
+	if m.err != nil {
+		return nil, m.err
+	}
+	return m.assign, nil
+}
+
+var _ PeerAssigner = &mockAssigner{}
+
+func TestPoolDetectAllEnded(t *testing.T) {
+	nw := 5
+	p2p := p2ptest.NewTestP2P(t)
+	ctx := context.Background()
+	ma := &mockAssigner{}
+	pool := newP2PBatchWorkerPool(p2p, nw)
+	st, err := util.NewBeaconState()
+	require.NoError(t, err)
+	keys, err := st.PublicKeys()
+	require.NoError(t, err)
+	v, err := newBackfillVerifier(st.GenesisValidatorsRoot(), keys)
+	require.NoError(t, err)
+	pool.spawn(ctx, nw, startup.NewClock(time.Now(), [32]byte{}), ma, v)
+	br := batcher{min: 10, size: 10}
+	endSeq := br.before(0)
+	require.Equal(t, batchEndSequence, endSeq.state)
+	for i := 0; i < nw; i++ {
+		pool.todo(endSeq)
+	}
+	b, err := pool.complete()
+	require.ErrorIs(t, err, errEndSequence)
+	require.Equal(t, b.end, endSeq.end)
+}
+
+type mockPool struct {
+	spawnCalled  []int
+	finishedChan chan batch
+	finishedErr  chan error
+	todoChan     chan batch
+}
+
+func (m *mockPool) spawn(_ context.Context, _ int, _ *startup.Clock, _ PeerAssigner, _ *verifier) {
+}
+
+func (m *mockPool) todo(b batch) {
+	m.todoChan <- b
+}
+
+func (m *mockPool) complete() (batch, error) {
+	select {
+	case b := <-m.finishedChan:
+		return b, nil
+	case err := <-m.finishedErr:
+		return batch{}, err
+	}
+}
+
+var _ batchWorkerPool = &mockPool{}

beacon-chain/sync/backfill/service.go

@@ -0,0 +1,300 @@
+package backfill
+
+import (
+	"context"
+
+	"github.com/libp2p/go-libp2p/core/peer"
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
+	"github.com/prysmaticlabs/prysm/v4/runtime"
+	"github.com/prysmaticlabs/prysm/v4/time/slots"
+	log "github.com/sirupsen/logrus"
+)
+
+type Service struct {
+	ctx           context.Context
+	store         *Store
+	ms            minimumSlotter
+	cw            startup.ClockWaiter
+	enabled       bool // service is disabled by default while feature is experimental
+	nWorkers      int
+	batchSeq      *batchSequencer
+	batchSize     uint64
+	pool          batchWorkerPool
+	verifier      *verifier
+	p2p           p2p.P2P
+	pa            PeerAssigner
+	batchImporter batchImporter
+}
+
+var _ runtime.Service = (*Service)(nil)
+
+type ServiceOption func(*Service) error
+
+func WithEnableBackfill(enabled bool) ServiceOption {
+	return func(s *Service) error {
+		s.enabled = enabled
+		return nil
+	}
+}
+
+func WithWorkerCount(n int) ServiceOption {
+	return func(s *Service) error {
+		s.nWorkers = n
+		return nil
+	}
+}
+
+func WithBatchSize(n uint64) ServiceOption {
+	return func(s *Service) error {
+		s.batchSize = n
+		return nil
+	}
+}
+
+type minimumSlotter interface {
+	minimumSlot() primitives.Slot
+	setClock(*startup.Clock)
+}
+
+type defaultMinimumSlotter struct {
+	clock *startup.Clock
+	cw    startup.ClockWaiter
+	ctx   context.Context
+}
+
+func (d defaultMinimumSlotter) minimumSlot() primitives.Slot {
+	if d.clock == nil {
+		var err error
+		d.clock, err = d.cw.WaitForClock(d.ctx)
+		if err != nil {
+			log.WithError(err).Fatal("failed to obtain system/genesis clock, unable to start backfill service")
+		}
+	}
+	return minimumBackfillSlot(d.clock.CurrentSlot())
+}
+
+func (d defaultMinimumSlotter) setClock(c *startup.Clock) {
+	//nolint:all
+	d.clock = c
+}
+
+var _ minimumSlotter = &defaultMinimumSlotter{}
+
+type batchImporter func(ctx context.Context, b batch, su *Store) (*dbval.BackfillStatus, error)
+
+func defaultBatchImporter(ctx context.Context, b batch, su *Store) (*dbval.BackfillStatus, error) {
+	status := su.status()
+	if err := b.ensureParent(bytesutil.ToBytes32(status.LowParentRoot)); err != nil {
+		return status, err
+	}
+	// Import blocks to db and update db state to reflect the newly imported blocks.
+	// Other parts of the beacon node may use the same StatusUpdater instance
+	// via the coverage.AvailableBlocker interface to safely determine if a given slot has been backfilled.
+	status, err := su.fillBack(ctx, b.results)
+	if err != nil {
+		log.WithError(err).Fatal("Non-recoverable db error in backfill service, quitting.")
+	}
+	return status, nil
+}
+
+// PeerAssigner describes a type that provides an Assign method, which can assign the best peer
+// to service an RPC request. The Assign method takes a map of peers that should be excluded,
+// allowing the caller to avoid making multiple concurrent requests to the same peer.
+type PeerAssigner interface {
+	Assign(busy map[peer.ID]bool, n int) ([]peer.ID, error)
+}
+
+// NewService initializes the backfill Service. Like all implementations of the Service interface,
+// the service won't begin its runloop until Start() is called.
+func NewService(ctx context.Context, su *Store, cw startup.ClockWaiter, p p2p.P2P, pa PeerAssigner, opts ...ServiceOption) (*Service, error) {
+	s := &Service{
+		ctx:           ctx,
+		store:         su,
+		cw:            cw,
+		ms:            &defaultMinimumSlotter{cw: cw, ctx: ctx},
+		p2p:           p,
+		pa:            pa,
+		batchImporter: defaultBatchImporter,
+	}
+	for _, o := range opts {
+		if err := o(s); err != nil {
+			return nil, err
+		}
+	}
+	s.pool = newP2PBatchWorkerPool(p, s.nWorkers)
+
+	return s, nil
+}
+
+func (s *Service) initVerifier(ctx context.Context) (*verifier, error) {
+	cps, err := s.store.originState(ctx)
+	if err != nil {
+		return nil, err
+	}
+	keys, err := cps.PublicKeys()
+	if err != nil {
+		return nil, errors.Wrap(err, "Unable to retrieve public keys for all validators in the origin state")
+	}
+	return newBackfillVerifier(cps.GenesisValidatorsRoot(), keys)
+}
+
+func (s *Service) updateComplete() bool {
+	b, err := s.pool.complete()
+	if err != nil {
+		if errors.Is(err, errEndSequence) {
+			log.WithField("backfill_slot", b.begin).Info("Backfill is complete")
+			return true
+		}
+		log.WithError(err).Fatal("Non-recoverable error in backfill service, quitting.")
+	}
+	s.batchSeq.update(b)
+	return false
+}
+
+func (s *Service) importBatches(ctx context.Context) {
+	importable := s.batchSeq.importable()
+	imported := 0
+	defer func() {
+		if imported == 0 {
+			return
+		}
+		backfillBatchesImported.Add(float64(imported))
+	}()
+	for i := range importable {
+		ib := importable[i]
+		if len(ib.results) == 0 {
+			log.WithFields(ib.logFields()).Error("Batch with no results, skipping importer.")
+		}
+		_, err := s.batchImporter(ctx, ib, s.store)
+		if err != nil {
+			log.WithError(err).WithFields(ib.logFields()).Debug("Backfill batch failed to import.")
+			s.downscore(ib)
+			s.batchSeq.update(ib.withState(batchErrRetryable))
+			// If a batch fails, the subsequent batches are no longer considered importable.
+			break
+		}
+		s.batchSeq.update(ib.withState(batchImportComplete))
+		imported += 1
+		// Calling update with state=batchImportComplete will advance the batch list.
+	}
+
+	nt := s.batchSeq.numTodo()
+	log.WithField("imported", imported).WithField("importable", len(importable)).
+		WithField("batches_remaining", nt).
+		Info("Backfill batches processed.")
+
+	backfillRemainingBatches.Set(float64(nt))
+}
+
+func (s *Service) scheduleTodos() {
+	batches, err := s.batchSeq.sequence()
+	if err != nil {
+		// This typically means we have several importable batches, but they are stuck behind a batch that needs
+		// to complete first so that we can chain parent roots across batches.
+		// ie backfilling [[90..100), [80..90), [70..80)], if we complete [70..80) and [80..90) but not [90..100),
+		// we can't move forward until [90..100) completes, because we need to confirm 99 connects to 100,
+		// and then we'll have the parent_root expected by 90 to ensure it matches the root for 89,
+		// at which point we know we can process [80..90).
+		if errors.Is(err, errMaxBatches) {
+			log.Debug("Backfill batches waiting for descendent batch to complete.")
+			return
+		}
+	}
+	for _, b := range batches {
+		s.pool.todo(b)
+	}
+}
+
+// Start begins the runloop of backfill.Service in the current goroutine.
+func (s *Service) Start() {
+	if !s.enabled {
+		log.Info("Exiting backfill service; not enabled.")
+		return
+	}
+	ctx, cancel := context.WithCancel(s.ctx)
+	defer func() {
+		cancel()
+	}()
+	clock, err := s.cw.WaitForClock(ctx)
+	if err != nil {
+		log.WithError(err).Fatal("Backfill service failed to start while waiting for genesis data.")
+	}
+	s.ms.setClock(clock)
+
+	status := s.store.status()
+	// Exit early if there aren't going to be any batches to backfill.
+	if primitives.Slot(status.LowSlot) <= s.ms.minimumSlot() {
+		log.WithField("minimum_required_slot", s.ms.minimumSlot()).
+			WithField("backfill_lowest_slot", status.LowSlot).
+			Info("Exiting backfill service; minimum block retention slot > lowest backfilled block.")
+		return
+	}
+	s.verifier, err = s.initVerifier(ctx)
+	if err != nil {
+		log.WithError(err).Fatal("Unable to initialize backfill verifier, quitting.")
+	}
+	s.pool.spawn(ctx, s.nWorkers, clock, s.pa, s.verifier)
+
+	s.batchSeq = newBatchSequencer(s.nWorkers, s.ms.minimumSlot(), primitives.Slot(status.LowSlot), primitives.Slot(s.batchSize))
+	if err = s.initBatches(); err != nil {
+		log.WithError(err).Fatal("Non-recoverable error in backfill service, quitting.")
+	}
+
+	for {
+		if ctx.Err() != nil {
+			return
+		}
+		if allComplete := s.updateComplete(); allComplete {
+			return
+		}
+		s.importBatches(ctx)
+		batchesWaiting.Set(float64(s.batchSeq.countWithState(batchImportable)))
+		if err := s.batchSeq.moveMinimum(s.ms.minimumSlot()); err != nil {
+			log.WithError(err).Fatal("Non-recoverable error in backfill service, quitting.")
+		}
+		s.scheduleTodos()
+	}
+}
+
+func (s *Service) initBatches() error {
+	batches, err := s.batchSeq.sequence()
+	if err != nil {
+		return err
+	}
+	for _, b := range batches {
+		s.pool.todo(b)
+	}
+	return nil
+}
+
+func (s *Service) downscore(b batch) {
+	s.p2p.Peers().Scorers().BadResponsesScorer().Increment(b.pid)
+}
+
+func (s *Service) Stop() error {
+	return nil
+}
+
+func (s *Service) Status() error {
+	return nil
+}
+
+// minimumBackfillSlot determines the lowest slot that backfill needs to download based on looking back
+// MIN_EPOCHS_FOR_BLOCK_REQUESTS from the current slot.
+func minimumBackfillSlot(current primitives.Slot) primitives.Slot {
+	oe := helpers.MinEpochsForBlockRequests()
+	if oe > slots.MaxSafeEpoch() {
+		oe = slots.MaxSafeEpoch()
+	}
+	offset := slots.UnsafeEpochStart(oe)
+	if offset > current {
+		return 0
+	}
+	return current - offset
+}

beacon-chain/sync/backfill/service_test.go

@@ -0,0 +1,89 @@
+package backfill
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	p2ptest "github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p/testing"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+	"github.com/prysmaticlabs/prysm/v4/testing/util"
+)
+
+type mockMinimumSlotter struct {
+	min primitives.Slot
+}
+
+var _ minimumSlotter = &mockMinimumSlotter{}
+
+func (m mockMinimumSlotter) minimumSlot() primitives.Slot {
+	return m.min
+}
+
+func (m mockMinimumSlotter) setClock(*startup.Clock) {
+}
+
+func TestServiceInit(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*300)
+	defer cancel()
+	db := &mockBackfillDB{}
+	su, err := NewUpdater(ctx, db)
+	require.NoError(t, err)
+	nWorkers := 5
+	var batchSize uint64 = 100
+	nBatches := nWorkers * 2
+	var high uint64 = 11235
+	originRoot := [32]byte{}
+	origin, err := util.NewBeaconState()
+	require.NoError(t, err)
+	db.states = map[[32]byte]state.BeaconState{originRoot: origin}
+	su.bs = &dbval.BackfillStatus{
+		LowSlot:    high,
+		OriginRoot: originRoot[:],
+	}
+	remaining := nBatches
+	cw := startup.NewClockSynchronizer()
+	require.NoError(t, cw.SetClock(startup.NewClock(time.Now(), [32]byte{})))
+	pool := &mockPool{todoChan: make(chan batch, nWorkers), finishedChan: make(chan batch, nWorkers)}
+	p2pt := p2ptest.NewTestP2P(t)
+	srv, err := NewService(ctx, su, cw, p2pt, &mockAssigner{}, WithBatchSize(batchSize), WithWorkerCount(nWorkers), WithEnableBackfill(true))
+	require.NoError(t, err)
+	srv.ms = mockMinimumSlotter{min: primitives.Slot(high - batchSize*uint64(nBatches))}
+	srv.pool = pool
+	srv.batchImporter = func(context.Context, batch, *Store) (*dbval.BackfillStatus, error) {
+		return &dbval.BackfillStatus{}, nil
+	}
+	go srv.Start()
+	todo := make([]batch, 0)
+	todo = testReadN(t, ctx, pool.todoChan, nWorkers, todo)
+	require.Equal(t, nWorkers, len(todo))
+	for i := 0; i < remaining; i++ {
+		b := todo[i]
+		if b.state == batchSequenced {
+			b.state = batchImportable
+		}
+		pool.finishedChan <- b
+		todo = testReadN(t, ctx, pool.todoChan, 1, todo)
+	}
+	require.Equal(t, remaining+nWorkers, len(todo))
+	for i := remaining; i < remaining+nWorkers; i++ {
+		require.Equal(t, batchEndSequence, todo[i].state)
+	}
+}
+
+func testReadN(t *testing.T, ctx context.Context, c chan batch, n int, into []batch) []batch {
+	for i := 0; i < n; i++ {
+		select {
+		case b := <-c:
+			into = append(into, b)
+		case <-ctx.Done():
+			// this means we hit the timeout, so something went wrong.
+			require.Equal(t, true, false)
+		}
+	}
+	return into
+}

beacon-chain/sync/backfill/status.go

@@ -2,121 +2,167 @@ package backfill
 
 import (
 	"context"
+	"sync"
 
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
 )
 
-// NewStatus correctly initializes a Status value with the required database value.
-func NewStatus(store DB) *Status {
-	return &Status{
+var errBatchDisconnected = errors.New("Highest block root in backfill batch doesn't match next parent_root")
+
+// NewUpdater correctly initializes a StatusUpdater value with the required database value.
+func NewUpdater(ctx context.Context, store BeaconDB) (*Store, error) {
+	s := &Store{
 		store: store,
 	}
+	status, err := s.store.BackfillStatus(ctx)
+	if err != nil {
+		if errors.Is(err, db.ErrNotFound) {
+			return s, s.recoverLegacy(ctx)
+		}
+		return nil, errors.Wrap(err, "db error while reading status of previous backfill")
+	}
+	s.swapStatus(status)
+	return s, nil
 }
 
-// Status provides a way to update and query the status of a backfill process that may be necessary to track when
+// Store provides a way to update and query the status of a backfill process that may be necessary to track when
 // a node was initialized via checkpoint sync. With checkpoint sync, there will be a gap in node history from genesis
-// until the checkpoint sync origin block. Status provides the means to update the value keeping track of the lower
-// end of the missing block range via the Advance() method, to check whether a Slot is missing from the database
-// via the SlotCovered() method, and to see the current StartGap() and EndGap().
-type Status struct {
-	start       primitives.Slot
-	end         primitives.Slot
-	store       DB
+// until the checkpoint sync origin block. Store provides the means to update the value keeping track of the lower
+// end of the missing block range via the FillFwd() method, to check whether a Slot is missing from the database
+// via the AvailableBlock() method, and to see the current StartGap() and EndGap().
+type Store struct {
+	sync.RWMutex
+	store       BeaconDB
 	genesisSync bool
+	bs          *dbval.BackfillStatus
 }
 
-// SlotCovered uses StartGap() and EndGap() to determine if the given slot is covered by the current chain history.
-// If the slot is <= StartGap(), or >= EndGap(), the result is true.
-// If the slot is between StartGap() and EndGap(), the result is false.
-func (s *Status) SlotCovered(sl primitives.Slot) bool {
+// AvailableBlock determines if the given slot is covered by the current chain history.
+// If the slot is <= backfill low slot, or >= backfill high slot, the result is true.
+// If the slot is between the backfill low and high slots, the result is false.
+func (s *Store) AvailableBlock(sl primitives.Slot) bool {
+	s.RLock()
+	defer s.RUnlock()
 	// short circuit if the node was synced from genesis
-	if s.genesisSync {
+	if s.genesisSync || sl == 0 || s.bs.LowSlot <= uint64(sl) {
 		return true
 	}
-	if s.StartGap() < sl && sl < s.EndGap() {
-		return false
-	}
-	return true
+	return false
 }
 
-// StartGap returns the slot at the beginning of the range that needs to be backfilled.
-func (s *Status) StartGap() primitives.Slot {
-	return s.start
+// Status is a threadsafe method to access a copy of the BackfillStatus value.
+func (s *Store) status() *dbval.BackfillStatus {
+	s.RLock()
+	defer s.RUnlock()
+	return &dbval.BackfillStatus{
+		LowSlot:       s.bs.LowSlot,
+		LowRoot:       s.bs.LowRoot,
+		LowParentRoot: s.bs.LowParentRoot,
+		OriginSlot:    s.bs.OriginSlot,
+		OriginRoot:    s.bs.OriginRoot,
+	}
 }
 
-// EndGap returns the slot at the end of the range that needs to be backfilled.
-func (s *Status) EndGap() primitives.Slot {
-	return s.end
+// fillBack saves the slice of blocks and updates the BackfillStatus LowSlot/Root/ParentRoot tracker to the values
+// from the first block in the slice. This method assumes that the block slice has been fully validated and
+// sorted in slot order by the calling function.
+func (s *Store) fillBack(ctx context.Context, blocks []blocks.ROBlock) (*dbval.BackfillStatus, error) {
+	status := s.status()
+	if len(blocks) == 0 {
+		return status, nil
+	}
+
+	highest := blocks[len(blocks)-1]
+	// The root of the highest block needs to match the parent root of the previous status. The backfill service will do
+	// the same check, but this is an extra defensive layer in front of the db index.
+	if highest.Root() != bytesutil.ToBytes32(status.LowParentRoot) {
+		return nil, errors.Wrapf(errBatchDisconnected, "prev parent_root=%#x, root=%#x, prev slot=%d, slot=%d",
+			status.LowParentRoot, highest.Root(), status.LowSlot, highest.Block().Slot())
+	}
+
+	if err := s.store.SaveROBlocks(ctx, blocks, false); err != nil {
+		return nil, errors.Wrapf(err, "error saving backfill blocks")
+	}
+
+	// Update finalized block index.
+	if err := s.store.BackfillFinalizedIndex(ctx, blocks, bytesutil.ToBytes32(status.LowRoot)); err != nil {
+		return nil, errors.Wrapf(err, "failed to update finalized index for batch, connecting root %#x to previously finalized block %#x",
+			highest.Root(), status.LowRoot)
+	}
+
+	// Update backfill status based on the block with the lowest slot in the batch.
+	lowest := blocks[0]
+	pr := lowest.Block().ParentRoot()
+	status.LowSlot = uint64(lowest.Block().Slot())
+	status.LowRoot = lowest.RootSlice()
+	status.LowParentRoot = pr[:]
+	return status, s.saveStatus(ctx, status)
 }
 
-var ErrAdvancePastOrigin = errors.New("cannot advance backfill Status beyond the origin checkpoint slot")
-
-// Advance advances the backfill position to the given slot & root.
-// It updates the backfill block root entry in the database,
-// and also updates the Status value's copy of the backfill position slot.
-func (s *Status) Advance(ctx context.Context, upTo primitives.Slot, root [32]byte) error {
-	if upTo > s.end {
-		return errors.Wrapf(ErrAdvancePastOrigin, "advance slot=%d, origin slot=%d", upTo, s.end)
+// recoverLegacy will check to see if the db is from a legacy checkpoint sync, and either build a new BackfillStatus
+// or label the node as synced from genesis.
+func (s *Store) recoverLegacy(ctx context.Context) error {
+	cpr, err := s.store.OriginCheckpointBlockRoot(ctx)
+	if errors.Is(err, db.ErrNotFoundOriginBlockRoot) {
+		s.genesisSync = true
+		return nil
 	}
-	s.start = upTo
-	return s.store.SaveBackfillBlockRoot(ctx, root)
+
+	cpb, err := s.store.Block(ctx, cpr)
+	if err != nil {
+		return errors.Wrapf(err, "error retrieving block for origin checkpoint root=%#x", cpr)
+	}
+	if err := blocks.BeaconBlockIsNil(cpb); err != nil {
+		return errors.Wrapf(err, "nil block found for origin checkpoint root=%#x", cpr)
+	}
+	os := uint64(cpb.Block().Slot())
+	lpr := cpb.Block().ParentRoot()
+	bs := &dbval.BackfillStatus{
+		LowSlot:       os,
+		LowRoot:       cpr[:],
+		LowParentRoot: lpr[:],
+		OriginSlot:    os,
+		OriginRoot:    cpr[:],
+	}
+	return s.saveStatus(ctx, bs)
 }
 
-// Reload queries the database for backfill status, initializing the internal data and validating the database state.
-func (s *Status) Reload(ctx context.Context) error {
-	cpRoot, err := s.store.OriginCheckpointBlockRoot(ctx)
-	if err != nil {
-		// mark genesis sync and short circuit further lookups
-		if errors.Is(err, db.ErrNotFoundOriginBlockRoot) {
-			s.genesisSync = true
-			return nil
-		}
-		return err
-	}
-	cpBlock, err := s.store.Block(ctx, cpRoot)
-	if err != nil {
-		return errors.Wrapf(err, "error retrieving block for origin checkpoint root=%#x", cpRoot)
-	}
-	if err := blocks.BeaconBlockIsNil(cpBlock); err != nil {
-		return err
-	}
-	s.end = cpBlock.Block().Slot()
-
-	_, err = s.store.GenesisBlockRoot(ctx)
-	if err != nil {
-		if errors.Is(err, db.ErrNotFoundGenesisBlockRoot) {
-			return errors.Wrap(err, "genesis block root required for checkpoint sync")
-		}
+func (s *Store) saveStatus(ctx context.Context, bs *dbval.BackfillStatus) error {
+	if err := s.store.SaveBackfillStatus(ctx, bs); err != nil {
 		return err
 	}
 
-	bfRoot, err := s.store.BackfillBlockRoot(ctx)
-	if err != nil {
-		if errors.Is(err, db.ErrNotFoundBackfillBlockRoot) {
-			return errors.Wrap(err, "found origin checkpoint block root, but no backfill block root")
-		}
-		return err
-	}
-	bfBlock, err := s.store.Block(ctx, bfRoot)
-	if err != nil {
-		return errors.Wrapf(err, "error retrieving block for backfill root=%#x", bfRoot)
-	}
-	if err := blocks.BeaconBlockIsNil(bfBlock); err != nil {
-		return err
-	}
-	s.start = bfBlock.Block().Slot()
+	s.swapStatus(bs)
 	return nil
 }
 
-// DB describes the set of DB methods that the Status type needs to function.
-type DB interface {
-	SaveBackfillBlockRoot(ctx context.Context, blockRoot [32]byte) error
-	GenesisBlockRoot(ctx context.Context) ([32]byte, error)
-	OriginCheckpointBlockRoot(ctx context.Context) ([32]byte, error)
-	BackfillBlockRoot(ctx context.Context) ([32]byte, error)
-	Block(ctx context.Context, blockRoot [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error)
+func (s *Store) swapStatus(bs *dbval.BackfillStatus) {
+	s.Lock()
+	defer s.Unlock()
+	s.bs = bs
+}
+
+// originState looks up the state for the checkpoint sync origin. This is a hack, because StatusUpdater is the only
+// thing that needs db access and it has the origin root handy, so it's convenient to look it up here. The state is
+// needed by the verifier.
+func (s *Store) originState(ctx context.Context) (state.BeaconState, error) {
+	return s.store.StateOrError(ctx, bytesutil.ToBytes32(s.status().OriginRoot))
+}
+
+// BeaconDB describes the set of DB methods that the StatusUpdater type needs to function.
+type BeaconDB interface {
+	SaveBackfillStatus(context.Context, *dbval.BackfillStatus) error
+	BackfillStatus(context.Context) (*dbval.BackfillStatus, error)
+	BackfillFinalizedIndex(ctx context.Context, blocks []blocks.ROBlock, finalizedChildRoot [32]byte) error
+	OriginCheckpointBlockRoot(context.Context) ([32]byte, error)
+	Block(context.Context, [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error)
+	SaveROBlocks(ctx context.Context, blks []blocks.ROBlock, cache bool) error
+	StateOrError(ctx context.Context, blockRoot [32]byte) (state.BeaconState, error)
 }

beacon-chain/sync/backfill/status_test.go

@@ -1,15 +1,18 @@
 package backfill
 
 import (
+	"bytes"
 	"context"
 	"testing"
 
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/db"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
 	blocktest "github.com/prysmaticlabs/prysm/v4/consensus-types/blocks/testing"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
+	"github.com/prysmaticlabs/prysm/v4/proto/dbval"
 
 	"github.com/pkg/errors"
-	"github.com/prysmaticlabs/prysm/v4/config/params"
 	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
 	"github.com/prysmaticlabs/prysm/v4/testing/require"
 	"github.com/prysmaticlabs/prysm/v4/testing/util"
@@ -19,121 +22,125 @@ var errEmptyMockDBMethod = errors.New("uninitialized mock db method called")
 
 type mockBackfillDB struct {
 	saveBackfillBlockRoot     func(ctx context.Context, blockRoot [32]byte) error
-	genesisBlockRoot          func(ctx context.Context) ([32]byte, error)
 	originCheckpointBlockRoot func(ctx context.Context) ([32]byte, error)
-	backfillBlockRoot         func(ctx context.Context) ([32]byte, error)
 	block                     func(ctx context.Context, blockRoot [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error)
+	saveBackfillStatus        func(ctx context.Context, status *dbval.BackfillStatus) error
+	backfillStatus            func(context.Context) (*dbval.BackfillStatus, error)
+	status                    *dbval.BackfillStatus
+	err                       error
+	states                    map[[32]byte]state.BeaconState
+	blocks                    map[[32]byte]blocks.ROBlock
 }
 
-var _ DB = &mockBackfillDB{}
+var _ BeaconDB = &mockBackfillDB{}
 
-func (db *mockBackfillDB) SaveBackfillBlockRoot(ctx context.Context, blockRoot [32]byte) error {
-	if db.saveBackfillBlockRoot != nil {
-		return db.saveBackfillBlockRoot(ctx, blockRoot)
+func (d *mockBackfillDB) StateOrError(_ context.Context, blockRoot [32]byte) (state.BeaconState, error) {
+	st, ok := d.states[blockRoot]
+	if !ok {
+		return nil, db.ErrNotFoundState
 	}
-	return errEmptyMockDBMethod
+	return st, nil
 }
 
-func (db *mockBackfillDB) GenesisBlockRoot(ctx context.Context) ([32]byte, error) {
-	if db.genesisBlockRoot != nil {
-		return db.genesisBlockRoot(ctx)
+func (d *mockBackfillDB) SaveBackfillStatus(ctx context.Context, status *dbval.BackfillStatus) error {
+	if d.saveBackfillStatus != nil {
+		return d.saveBackfillStatus(ctx, status)
+	}
+	d.status = status
+	return nil
+}
+
+func (d *mockBackfillDB) BackfillStatus(ctx context.Context) (*dbval.BackfillStatus, error) {
+	if d.backfillStatus != nil {
+		return d.backfillStatus(ctx)
+	}
+	return d.status, nil
+}
+
+func (d *mockBackfillDB) OriginCheckpointBlockRoot(ctx context.Context) ([32]byte, error) {
+	if d.originCheckpointBlockRoot != nil {
+		return d.originCheckpointBlockRoot(ctx)
 	}
 	return [32]byte{}, errEmptyMockDBMethod
 }
 
-func (db *mockBackfillDB) OriginCheckpointBlockRoot(ctx context.Context) ([32]byte, error) {
-	if db.originCheckpointBlockRoot != nil {
-		return db.originCheckpointBlockRoot(ctx)
+func (d *mockBackfillDB) Block(ctx context.Context, blockRoot [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
+	if d.block != nil {
+		return d.block(ctx, blockRoot)
 	}
-	return [32]byte{}, errEmptyMockDBMethod
+	b, ok := d.blocks[blockRoot]
+	if !ok {
+		return nil, db.ErrNotFound
+	}
+	return b, nil
 }
 
-func (db *mockBackfillDB) BackfillBlockRoot(ctx context.Context) ([32]byte, error) {
-	if db.backfillBlockRoot != nil {
-		return db.backfillBlockRoot(ctx)
+func (d *mockBackfillDB) SaveROBlocks(ctx context.Context, blks []blocks.ROBlock, cache bool) error {
+	if d.blocks == nil {
+		d.blocks = make(map[[32]byte]blocks.ROBlock)
 	}
-	return [32]byte{}, errEmptyMockDBMethod
+	for i := range blks {
+		d.blocks[blks[i].Root()] = blks[i]
+	}
+	return nil
 }
 
-func (db *mockBackfillDB) Block(ctx context.Context, blockRoot [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-	if db.block != nil {
-		return db.block(ctx, blockRoot)
-	}
-	return nil, errEmptyMockDBMethod
+func (d *mockBackfillDB) BackfillFinalizedIndex(ctx context.Context, blocks []blocks.ROBlock, finalizedChildRoot [32]byte) error {
+	return nil
 }
 
 func TestSlotCovered(t *testing.T) {
 	cases := []struct {
 		name   string
 		slot   primitives.Slot
-		status *Status
+		status *Store
 		result bool
 	}{
 		{
-			name:   "below start true",
-			status: &Status{start: 1},
+			name:   "genesis true",
+			status: &Store{bs: &dbval.BackfillStatus{LowSlot: 10}},
 			slot:   0,
 			result: true,
 		},
 		{
 			name:   "above end true",
-			status: &Status{end: 1},
+			status: &Store{bs: &dbval.BackfillStatus{LowSlot: 1}},
 			slot:   2,
 			result: true,
 		},
 		{
 			name:   "equal end true",
-			status: &Status{end: 1},
+			status: &Store{bs: &dbval.BackfillStatus{LowSlot: 1}},
 			slot:   1,
 			result: true,
 		},
-		{
-			name:   "equal start true",
-			status: &Status{start: 2},
-			slot:   2,
-			result: true,
-		},
-		{
-			name:   "between false",
-			status: &Status{start: 1, end: 3},
-			slot:   2,
-			result: false,
-		},
 		{
 			name:   "genesisSync always true",
-			status: &Status{genesisSync: true},
+			status: &Store{genesisSync: true},
 			slot:   100,
 			result: true,
 		},
 	}
 	for _, c := range cases {
-		result := c.status.SlotCovered(c.slot)
-		require.Equal(t, c.result, result)
+		t.Run(c.name, func(t *testing.T) {
+			result := c.status.AvailableBlock(c.slot)
+			require.Equal(t, c.result, result)
+		})
 	}
 }
 
-func TestAdvance(t *testing.T) {
+func TestStatusUpdater_FillBack(t *testing.T) {
 	ctx := context.Background()
-	saveBackfillBuf := make([][32]byte, 0)
-	mdb := &mockBackfillDB{
-		saveBackfillBlockRoot: func(ctx context.Context, root [32]byte) error {
-			saveBackfillBuf = append(saveBackfillBuf, root)
-			return nil
-		},
-	}
-	s := &Status{end: 100, store: mdb}
-	var root [32]byte
-	copy(root[:], []byte{0x23, 0x23})
-	require.NoError(t, s.Advance(ctx, 90, root))
-	require.Equal(t, root, saveBackfillBuf[0])
-	not := s.SlotCovered(95)
-	require.Equal(t, false, not)
-
-	// this should still be len 1 after failing to advance
-	require.Equal(t, 1, len(saveBackfillBuf))
-	require.ErrorIs(t, s.Advance(ctx, s.end+1, root), ErrAdvancePastOrigin)
-	// this has an element in it from the previous test, there shouldn't be an additional one
-	require.Equal(t, 1, len(saveBackfillBuf))
+	mdb := &mockBackfillDB{}
+	b, err := setupTestBlock(90)
+	require.NoError(t, err)
+	rob, err := blocks.NewROBlock(b)
+	require.NoError(t, err)
+	s := &Store{bs: &dbval.BackfillStatus{LowSlot: 100, LowParentRoot: rob.RootSlice()}, store: mdb}
+	require.Equal(t, false, s.AvailableBlock(95))
+	_, err = s.fillBack(ctx, []blocks.ROBlock{rob})
+	require.NoError(t, err)
+	require.Equal(t, true, s.AvailableBlock(95))
 }
 
 func goodBlockRoot(root [32]byte) func(ctx context.Context) ([32]byte, error) {
@@ -151,9 +158,8 @@ func setupTestBlock(slot primitives.Slot) (interfaces.ReadOnlySignedBeaconBlock,
 	return blocktest.SetBlockSlot(b, slot)
 }
 
-func TestReload(t *testing.T) {
+func TestNewUpdater(t *testing.T) {
 	ctx := context.Background()
-	derp := errors.New("derp")
 
 	originSlot := primitives.Slot(100)
 	var originRoot [32]byte
@@ -163,164 +169,39 @@ func TestReload(t *testing.T) {
 
 	backfillSlot := primitives.Slot(50)
 	var backfillRoot [32]byte
-	copy(originRoot[:], []byte{0x02})
+	copy(backfillRoot[:], []byte{0x02})
 	backfillBlock, err := setupTestBlock(backfillSlot)
 	require.NoError(t, err)
-
+	var parentRoot [32]byte
+	copy(parentRoot[:], []byte{0x03})
+	var rootSlice = func(r [32]byte) []byte { return r[:] }
+	typicalBackfillStatus := &dbval.BackfillStatus{
+		LowSlot:       23,
+		LowRoot:       backfillRoot[:],
+		LowParentRoot: parentRoot[:],
+		OriginSlot:    1123,
+		OriginRoot:    originRoot[:],
+	}
 	cases := []struct {
 		name     string
-		db       DB
+		db       BeaconDB
 		err      error
-		expected *Status
+		expected *Store
 	}{
-		/*{
+		{
 			name: "origin not found, implying genesis sync ",
 			db: &mockBackfillDB{
-				genesisBlockRoot: goodBlockRoot(params.BeaconConfig().ZeroHash),
+				backfillStatus: func(context.Context) (*dbval.BackfillStatus, error) {
+					return nil, db.ErrNotFound
+				},
 				originCheckpointBlockRoot: func(ctx context.Context) ([32]byte, error) {
 					return [32]byte{}, db.ErrNotFoundOriginBlockRoot
 				}},
-			expected: &Status{genesisSync: true},
+			expected: &Store{genesisSync: true},
 		},
 		{
-			name: "genesis not found error",
-			err:  db.ErrNotFoundGenesisBlockRoot,
+			name: "legacy recovery",
 			db: &mockBackfillDB{
-				genesisBlockRoot: func(ctx context.Context) ([32]byte, error) {
-					return [32]byte{}, db.ErrNotFoundGenesisBlockRoot
-				},
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					switch root {
-					case originRoot:
-						return originBlock, nil
-					}
-					return nil, nil
-				},
-			},
-		},
-		{
-			name: "other genesis error",
-			err:  derp,
-			db: &mockBackfillDB{
-				genesisBlockRoot: func(ctx context.Context) ([32]byte, error) {
-					return [32]byte{}, derp
-				},
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					switch root {
-					case originRoot:
-						return originBlock, nil
-					}
-					return nil, nil
-				},
-			},
-		},
-		{
-			name: "origin other error",
-			db: &mockBackfillDB{
-				genesisBlockRoot: goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: func(ctx context.Context) ([32]byte, error) {
-					return [32]byte{}, derp
-				}},
-			err: derp,
-		},
-		{
-			name: "origin root found, block missing",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					return nil, nil
-				},
-			},
-			err: blocks.ErrNilSignedBeaconBlock,
-		},
-		{
-			name: "origin root found, block error",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					return nil, derp
-				},
-			},
-			err: derp,
-		},
-		{
-			name: "origin root found, block found, backfill root not found",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					return originBlock, nil
-				},
-				backfillBlockRoot: func(ctx context.Context) ([32]byte, error) {
-					return [32]byte{}, db.ErrNotFoundBackfillBlockRoot
-				},
-			},
-			err: db.ErrNotFoundBackfillBlockRoot,
-		},
-		{
-			name: "origin root found, block found, random backfill root err",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					switch root {
-					case originRoot:
-						return originBlock, nil
-					case backfillRoot:
-						return nil, nil
-					}
-					return nil, derp
-				},
-				backfillBlockRoot: func(ctx context.Context) ([32]byte, error) {
-					return [32]byte{}, derp
-				},
-			},
-			err: derp,
-		},
-		{
-			name: "origin root found, block found, backfill root found, backfill block not found",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					switch root {
-					case originRoot:
-						return originBlock, nil
-					case backfillRoot:
-						return nil, nil
-					}
-					return nil, derp
-				},
-				backfillBlockRoot: goodBlockRoot(backfillRoot),
-			},
-			err: blocks.ErrNilSignedBeaconBlock,
-		},
-		{
-			name: "origin root found, block found, backfill root found, backfill block random err",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
-				originCheckpointBlockRoot: goodBlockRoot(originRoot),
-				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
-					switch root {
-					case originRoot:
-						return originBlock, nil
-					case backfillRoot:
-						return nil, derp
-					}
-					return nil, errors.New("not derp")
-				},
-				backfillBlockRoot: goodBlockRoot(backfillRoot),
-			},
-			err: derp,
-		},*/
-		{
-			name: "complete happy path",
-			db: &mockBackfillDB{
-				genesisBlockRoot:          goodBlockRoot(params.BeaconConfig().ZeroHash),
 				originCheckpointBlockRoot: goodBlockRoot(originRoot),
 				block: func(ctx context.Context, root [32]byte) (interfaces.ReadOnlySignedBeaconBlock, error) {
 					switch root {
@@ -331,28 +212,44 @@ func TestReload(t *testing.T) {
 					}
 					return nil, errors.New("not derp")
 				},
-				backfillBlockRoot: goodBlockRoot(backfillRoot),
+				backfillStatus: func(context.Context) (*dbval.BackfillStatus, error) { return nil, db.ErrNotFound },
 			},
-			err:      derp,
-			expected: &Status{genesisSync: false, start: backfillSlot, end: originSlot},
+			expected: &Store{bs: &dbval.BackfillStatus{
+				LowSlot: uint64(originSlot), OriginSlot: uint64(originSlot),
+				LowRoot: originRoot[:], OriginRoot: originRoot[:], LowParentRoot: rootSlice(originBlock.Block().ParentRoot()),
+			}},
+		},
+		{
+			name: "backfill found",
+			db: &mockBackfillDB{backfillStatus: func(ctx context.Context) (*dbval.BackfillStatus, error) {
+				return typicalBackfillStatus, nil
+			}},
+			expected: &Store{bs: typicalBackfillStatus},
 		},
 	}
 
 	for _, c := range cases {
-		s := &Status{
-			store: c.db,
-		}
-		err := s.Reload(ctx)
-		if err != nil {
-			require.ErrorIs(t, err, c.err)
-			continue
-		}
-		require.NoError(t, err)
-		if c.expected == nil {
-			continue
-		}
-		require.Equal(t, c.expected.genesisSync, s.genesisSync)
-		require.Equal(t, c.expected.start, s.start)
-		require.Equal(t, c.expected.end, s.end)
+		t.Run(c.name, func(t *testing.T) {
+			s, err := NewUpdater(ctx, c.db)
+			if c.err != nil {
+				require.ErrorIs(t, err, c.err)
+				return
+			}
+			require.NoError(t, err)
+			if c.expected == nil {
+				return
+			}
+			require.Equal(t, c.expected.genesisSync, s.genesisSync)
+			if c.expected.genesisSync {
+				require.IsNil(t, s.bs)
+				return
+			}
+			require.Equal(t, c.expected.bs.LowSlot, s.bs.LowSlot)
+			require.Equal(t, c.expected.bs.OriginSlot, s.bs.OriginSlot)
+			require.Equal(t, true, bytes.Equal(c.expected.bs.OriginRoot, s.bs.OriginRoot))
+			require.Equal(t, true, bytes.Equal(c.expected.bs.LowRoot, s.bs.LowRoot))
+			require.Equal(t, true, bytes.Equal(c.expected.bs.LowParentRoot, s.bs.LowParentRoot))
+		})
 	}
+
 }

beacon-chain/sync/backfill/verify.go

@@ -0,0 +1,125 @@
+package backfill
+
+import (
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/core/signing"
+	fieldparams "github.com/prysmaticlabs/prysm/v4/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/v4/config/params"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/crypto/bls"
+	"github.com/prysmaticlabs/prysm/v4/network/forks"
+	"github.com/prysmaticlabs/prysm/v4/time/slots"
+)
+
+var errInvalidBatchChain = errors.New("parent_root of block does not match the previous block's root")
+var errProposerIndexTooHigh = errors.New("proposer index not present in origin state")
+var errUnknownDomain = errors.New("runtime error looking up signing domain for fork")
+
+// VerifiedROBlocks represents a slice of blocks that have passed signature verification.
+type VerifiedROBlocks []blocks.ROBlock
+
+type verifier struct {
+	keys   [][fieldparams.BLSPubkeyLength]byte
+	maxVal primitives.ValidatorIndex
+	domain *domainCache
+}
+
+// TODO: rewrite this to use ROBlock.
+func (vr verifier) verify(blks []interfaces.ReadOnlySignedBeaconBlock) (VerifiedROBlocks, error) {
+	var err error
+	result := make([]blocks.ROBlock, len(blks))
+	sigSet := bls.NewSet()
+	for i := range blks {
+		result[i], err = blocks.NewROBlock(blks[i])
+		if err != nil {
+			return nil, err
+		}
+		if i > 0 && result[i-1].Root() != result[i].Block().ParentRoot() {
+			p, b := result[i-1], result[i]
+			return nil, errors.Wrapf(errInvalidBatchChain,
+				"slot %d parent_root=%#x, slot %d root=%#x",
+				b.Block().Slot(), b.Block().ParentRoot(),
+				p.Block().Slot(), p.Root())
+		}
+		set, err := vr.blockSignatureBatch(result[i])
+		if err != nil {
+			return nil, err
+		}
+		sigSet.Join(set)
+	}
+	v, err := sigSet.Verify()
+	if err != nil {
+		return nil, errors.Wrap(err, "block signature verification error")
+	}
+	if !v {
+		return nil, errors.New("batch block signature verification failed")
+	}
+	return result, nil
+}
+
+func (vr verifier) blockSignatureBatch(b blocks.ROBlock) (*bls.SignatureBatch, error) {
+	pidx := b.Block().ProposerIndex()
+	if pidx > vr.maxVal {
+		return nil, errProposerIndexTooHigh
+	}
+	dom, err := vr.domain.forEpoch(slots.ToEpoch(b.Block().Slot()))
+	if err != nil {
+		return nil, err
+	}
+	sig := b.Signature()
+	pk := vr.keys[pidx][:]
+	root := b.Root()
+	rootF := func() ([32]byte, error) { return root, nil }
+	return signing.BlockSignatureBatch(pk, sig[:], dom, rootF)
+}
+
+func newBackfillVerifier(vr []byte, keys [][fieldparams.BLSPubkeyLength]byte) (*verifier, error) {
+	dc, err := newDomainCache(vr, params.BeaconConfig().DomainBeaconProposer,
+		forks.NewOrderedSchedule(params.BeaconConfig()))
+	if err != nil {
+		return nil, err
+	}
+	v := &verifier{
+		keys:   keys,
+		domain: dc,
+	}
+	v.maxVal = primitives.ValidatorIndex(len(v.keys) - 1)
+	return v, nil
+}
+
+// domainCache provides a fast signing domain lookup by epoch.
+type domainCache struct {
+	fsched      forks.OrderedSchedule
+	forkDomains map[[4]byte][]byte
+	dType       [bls.DomainByteLength]byte
+}
+
+func newDomainCache(vRoot []byte, dType [bls.DomainByteLength]byte, fsched forks.OrderedSchedule) (*domainCache, error) {
+	dc := &domainCache{
+		fsched:      fsched,
+		forkDomains: make(map[[4]byte][]byte),
+		dType:       dType,
+	}
+	for _, entry := range fsched {
+		d, err := signing.ComputeDomain(dc.dType, entry.Version[:], vRoot)
+		if err != nil {
+			return nil, errors.Wrapf(err, "failed to pre-compute signing domain for fork version=%#x", entry.Version)
+		}
+		dc.forkDomains[entry.Version] = d
+	}
+	return dc, nil
+}
+
+func (dc *domainCache) forEpoch(e primitives.Epoch) ([]byte, error) {
+	fork, err := dc.fsched.VersionForEpoch(e)
+	if err != nil {
+		return nil, err
+	}
+	d, ok := dc.forkDomains[fork]
+	if !ok {
+		return nil, errors.Wrapf(errUnknownDomain, "fork version=%#x, epoch=%d", fork, e)
+	}
+	return d, nil
+}

beacon-chain/sync/backfill/verify_test.go

@@ -0,0 +1,75 @@
+package backfill
+
+import (
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/core/signing"
+	fieldparams "github.com/prysmaticlabs/prysm/v4/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/v4/config/params"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/blocks"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/interfaces"
+	"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
+	"github.com/prysmaticlabs/prysm/v4/crypto/bls"
+	"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/v4/network/forks"
+	"github.com/prysmaticlabs/prysm/v4/runtime/interop"
+	"github.com/prysmaticlabs/prysm/v4/testing/require"
+	"github.com/prysmaticlabs/prysm/v4/testing/util"
+)
+
+func TestDomainCache(t *testing.T) {
+	cfg := params.MainnetConfig()
+	vRoot, err := hexutil.Decode("0x0011223344556677889900112233445566778899001122334455667788990011")
+	dType := cfg.DomainBeaconProposer
+	require.NoError(t, err)
+	require.Equal(t, 32, len(vRoot))
+	fsched := forks.NewOrderedSchedule(cfg)
+	dc, err := newDomainCache(vRoot,
+		dType, fsched)
+	require.NoError(t, err)
+	require.Equal(t, len(fsched), len(dc.forkDomains))
+	for i := range fsched {
+		e := fsched[i].Epoch
+		ad, err := dc.forEpoch(e)
+		require.NoError(t, err)
+		ed, err := signing.ComputeDomain(dType, fsched[i].Version[:], vRoot)
+		require.NoError(t, err)
+		require.DeepEqual(t, ed, ad)
+	}
+}
+
+func testBlocksWithKeys(t *testing.T, nBlocks uint64, nBlobs int, vr []byte) ([]blocks.ROBlock, [][]blocks.ROBlob, []bls.SecretKey, []bls.PublicKey) {
+	blks := make([]blocks.ROBlock, nBlocks)
+	blbs := make([][]blocks.ROBlob, nBlocks)
+	sks, pks, err := interop.DeterministicallyGenerateKeys(0, nBlocks)
+	require.NoError(t, err)
+	prevRoot := [32]byte{}
+	for i := uint64(0); i < nBlocks; i++ {
+		block, blobs := util.GenerateTestDenebBlockWithSidecar(t, prevRoot, primitives.Slot(i), nBlobs, util.WithProposerSigning(primitives.ValidatorIndex(i), sks[i], vr))
+		prevRoot = block.Root()
+		blks[i] = block
+		blbs[i] = blobs
+	}
+	return blks, blbs, sks, pks
+}
+
+func TestVerify(t *testing.T) {
+	vr := make([]byte, 32)
+	copy(vr, []byte("yooooo"))
+	blks, _, _, pks := testBlocksWithKeys(t, 2, 0, vr)
+	pubkeys := make([][fieldparams.BLSPubkeyLength]byte, len(pks))
+	for i := range pks {
+		pubkeys[i] = bytesutil.ToBytes48(pks[i].Marshal())
+	}
+	v, err := newBackfillVerifier(vr, pubkeys)
+	require.NoError(t, err)
+	notrob := make([]interfaces.ReadOnlySignedBeaconBlock, len(blks))
+	// We have to unwrap the ROBlocks for this code because that's what it expects (for now).
+	for i := range blks {
+		notrob[i] = blks[i].ReadOnlySignedBeaconBlock
+	}
+	vbs, err := v.verify(notrob)
+	require.NoError(t, err)
+	require.Equal(t, len(blks), len(vbs))
+}

beacon-chain/sync/backfill/worker.go

@@ -0,0 +1,72 @@
+package backfill
+
+import (
+	"context"
+	"time"
+
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/p2p"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/startup"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync"
+	log "github.com/sirupsen/logrus"
+)
+
+type workerId int
+
+type p2pWorker struct {
+	id   workerId
+	todo chan batch
+	done chan batch
+	p2p  p2p.P2P
+	v    *verifier
+	c    *startup.Clock
+}
+
+func (w *p2pWorker) run(ctx context.Context) {
+	for {
+		select {
+		case b := <-w.todo:
+			log.WithFields(b.logFields()).WithField("backfill_worker", w.id).Debug("Backfill worker received batch.")
+			w.done <- w.handle(ctx, b)
+		case <-ctx.Done():
+			log.WithField("backfill_worker", w.id).Info("Backfill worker exiting after context canceled.")
+			return
+		}
+	}
+}
+
+func (w *p2pWorker) handle(ctx context.Context, b batch) batch {
+	start := time.Now()
+	results, err := sync.SendBeaconBlocksByRangeRequest(ctx, w.c, w.p2p, b.pid, b.request(), nil)
+	dlt := time.Now()
+	backfillBatchTimeDownloading.Observe(float64(dlt.Sub(start).Milliseconds()))
+	if err != nil {
+		return b.withRetryableError(err)
+	}
+	vb, err := w.v.verify(results)
+	backfillBatchTimeVerifying.Observe(float64(time.Since(dlt).Milliseconds()))
+	if err != nil {
+		return b.withRetryableError(err)
+	}
+	// This is a hack to get the rough size of the batch. This helps us approximate the amount of memory needed
+	// to hold batches and relative sizes between batches, but will be inaccurate when it comes to measuring actual
+	// bytes downloaded from peers, mainly because the p2p messages are snappy compressed.
+	bdl := 0
+	for i := range vb {
+		bdl += vb[i].SizeSSZ()
+	}
+	backfillBatchApproximateBytes.Add(float64(bdl))
+	log.WithField("dlbytes", bdl).Debug("backfill batch bytes downloaded")
+	b.results = vb
+	return b.withState(batchImportable)
+}
+
+func newP2pWorker(id workerId, p p2p.P2P, todo, done chan batch, c *startup.Clock, v *verifier) *p2pWorker {
+	return &p2pWorker{
+		id:   id,
+		todo: todo,
+		done: done,
+		p2p:  p,
+		v:    v,
+		c:    c,
+	}
+}

beacon-chain/verification/cache_test.go

@@ -18,7 +18,7 @@ import (
 func testSignedBlockBlobKeys(t *testing.T, valRoot []byte, slot primitives.Slot, nblobs int) (blocks.ROBlock, []blocks.ROBlob, bls.SecretKey, bls.PublicKey) {
 	sks, pks, err := interop.DeterministicallyGenerateKeys(0, 1)
 	require.NoError(t, err)
-	block, blobs := util.GenerateTestDenebBlockWithSidecar(t, [32]byte{}, slot, nblobs, util.WithProposerSigning(0, sks[0], pks[0], valRoot))
+	block, blobs := util.GenerateTestDenebBlockWithSidecar(t, [32]byte{}, slot, nblobs, util.WithProposerSigning(0, sks[0], valRoot))
 	return block, blobs, sks[0], pks[0]
 }
 

cmd/beacon-chain/BUILD.bazel

@@ -21,6 +21,7 @@ go_library(
         "//cmd/beacon-chain/flags:go_default_library",
         "//cmd/beacon-chain/jwt:go_default_library",
         "//cmd/beacon-chain/storage:go_default_library",
+        "//cmd/beacon-chain/sync/backfill:go_default_library",
         "//cmd/beacon-chain/sync/checkpoint:go_default_library",
         "//cmd/beacon-chain/sync/genesis:go_default_library",
         "//config/features:go_default_library",

cmd/beacon-chain/main.go

@@ -20,6 +20,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/flags"
 	jwtcommands "github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/jwt"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/storage"
+	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/backfill"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/checkpoint"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/genesis"
 	"github.com/prysmaticlabs/prysm/v4/config/features"
@@ -138,6 +139,9 @@ var appFlags = []cli.Flag{
 	flags.JwtId,
 	storage.BlobStoragePathFlag,
 	storage.BlobRetentionEpochFlag,
+	backfill.EnableExperimentalBackfill,
+	backfill.BackfillBatchSize,
+	backfill.BackfillWorkerCount,
 }
 
 func init() {
@@ -287,6 +291,7 @@ func startNode(ctx *cli.Context, cancel context.CancelFunc) error {
 		genesis.BeaconNodeOptions,
 		checkpoint.BeaconNodeOptions,
 		storage.BeaconNodeOptions,
+		backfill.BeaconNodeOptions,
 	}
 	for _, of := range optFuncs {
 		ofo, err := of(ctx)

cmd/beacon-chain/sync/backfill/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["options.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/backfill",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//beacon-chain/node:go_default_library",
+        "//beacon-chain/sync/backfill:go_default_library",
+        "@com_github_urfave_cli_v2//:go_default_library",
+    ],
+)

cmd/beacon-chain/sync/backfill/options.go

@@ -0,0 +1,53 @@
+package backfill
+
+import (
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/node"
+	"github.com/prysmaticlabs/prysm/v4/beacon-chain/sync/backfill"
+	"github.com/urfave/cli/v2"
+)
+
+var (
+	backfillBatchSizeName   = "backfill-batch-size"
+	backfillWorkerCountName = "backfill-worker-count"
+	// EnableExperimentalBackfill enables backfill for checkpoint synced nodes.
+	// This flag will be removed onced backfill is enabled by default.
+	EnableExperimentalBackfill = &cli.BoolFlag{
+		Name: "enable-experimental-backfill",
+		Usage: "Backfill is still experimental at this time." +
+			"It will only be enabled if this flag is specified and the node was started using checkpoint sync.",
+	}
+	// BackfillBatchSize allows users to tune block backfill request sizes to maximize network utilization
+	// at the cost of higher memory.
+	BackfillBatchSize = &cli.Uint64Flag{
+		Name: backfillBatchSizeName,
+		Usage: "Number of blocks per backfill batch. " +
+			"A larger number will request more blocks at once from peers, but also consume more system memory to " +
+			"hold batches in memory during processing. This has a multiplicative effect with " + backfillWorkerCountName,
+		Value: 64,
+	}
+	// BackfillWorkerCount allows users to tune the number of concurrent backfill batches to download, to maximize
+	// network utilization at the cost of higher memory.
+	BackfillWorkerCount = &cli.IntFlag{
+		Name: backfillWorkerCountName,
+		Usage: "Number of concurrent backfill batch requests. " +
+			"A larger number will better utilize network resources, up to a system-dependent limit, but will also " +
+			"consume more system memory to hold batches in memory during processing. Multiply by backfill-batch-size and " +
+			"average block size (~2MB before deneb) to find the right number for your system. " +
+			"This has a multiplicatice effect with " + backfillBatchSizeName,
+		Value: 2,
+	}
+)
+
+// BeaconNodeOptions sets the appropriate functional opts on the *node.BeaconNode value, to decouple options
+// from flag parsing.
+func BeaconNodeOptions(c *cli.Context) ([]node.Option, error) {
+	opt := func(node *node.BeaconNode) (err error) {
+		node.BackfillOpts = []backfill.ServiceOption{
+			backfill.WithBatchSize(c.Uint64(BackfillBatchSize.Name)),
+			backfill.WithWorkerCount(c.Int(BackfillWorkerCount.Name)),
+			backfill.WithEnableBackfill(c.Bool(EnableExperimentalBackfill.Name)),
+		}
+		return nil
+	}
+	return []node.Option{opt}, nil
+}

cmd/beacon-chain/usage.go

@@ -8,6 +8,7 @@ import (
 	"github.com/prysmaticlabs/prysm/v4/cmd"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/flags"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/storage"
+	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/backfill"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/checkpoint"
 	"github.com/prysmaticlabs/prysm/v4/cmd/beacon-chain/sync/genesis"
 	"github.com/prysmaticlabs/prysm/v4/config/features"
@@ -136,6 +137,9 @@ var appHelpFlagGroups = []flagGroup{
 			genesis.BeaconAPIURL,
 			storage.BlobStoragePathFlag,
 			storage.BlobRetentionEpochFlag,
+			backfill.EnableExperimentalBackfill,
+			backfill.BackfillWorkerCount,
+			backfill.BackfillBatchSize,
 		},
 	},
 	{

config/params/configset.go

@@ -114,6 +114,9 @@ func (r *configset) replace(cfg *BeaconChainConfig) error {
 func (r *configset) replaceWithUndo(cfg *BeaconChainConfig) (func() error, error) {
 	name := cfg.ConfigName
 	prev := r.nameToConfig[name]
+	if prev != nil {
+		prev = prev.Copy()
+	}
 	if err := r.replace(cfg); err != nil {
 		return nil, err
 	}
@@ -142,7 +145,11 @@ func (r *configset) setActive(c *BeaconChainConfig) error {
 }
 
 func (r *configset) setActiveWithUndo(c *BeaconChainConfig) (func() error, error) {
-	active := r.active
+	if r.active == nil {
+		return nil, errors.Wrap(errCannotNullifyActive,
+			"active config is currently nil, refusing to construct undo method that will leave it nil again")
+	}
+	active := r.active.Copy()
 	r.active = c
 	undo, err := r.replaceWithUndo(c)
 	if err != nil {

config/params/testutils.go

@@ -11,15 +11,30 @@ func SetupTestConfigCleanup(t testing.TB) {
 	temp := configs.getActive().Copy()
 	undo, err := SetActiveWithUndo(temp)
 	if err != nil {
-		t.Error(err)
+		t.Fatal(err)
 	}
 	prevNetworkCfg := networkConfig.Copy()
 	t.Cleanup(func() {
 		mainnetBeaconConfig = prevDefaultBeaconConfig
 		err = undo()
 		if err != nil {
-			t.Error(err)
+			t.Fatal(err)
 		}
 		networkConfig = prevNetworkCfg
 	})
 }
+
+// SetActiveTestCleanup sets an active config,
+// and adds a test cleanup hook to revert to the default config after the test completes.
+func SetActiveTestCleanup(t *testing.T, cfg *BeaconChainConfig) {
+	undo, err := SetActiveWithUndo(cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		err = undo()
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+}

consensus-types/blocks/roblock.go

@@ -20,6 +20,14 @@ func (b ROBlock) Root() [32]byte {
 	return b.root
 }
 
+// RootSlice returns a slice of the value returned by Root(). This is convenient because slicing the result of a func
+// is not allowed, so only offering a fixed-length array version results in boilerplate code to
+func (b ROBlock) RootSlice() []byte {
+	r := make([]byte, 32)
+	copy(r, b.root[:])
+	return r
+}
+
 // NewROBlockWithRoot creates an ROBlock embedding the given block with its root. It accepts the root as parameter rather than
 // computing it internally, because in some cases a block is retrieved by its root and recomputing it is a waste.
 func NewROBlockWithRoot(b interfaces.ReadOnlySignedBeaconBlock, root [32]byte) (ROBlock, error) {
@@ -42,6 +50,20 @@ func NewROBlock(b interfaces.ReadOnlySignedBeaconBlock) (ROBlock, error) {
 	return ROBlock{ReadOnlySignedBeaconBlock: b, root: root}, nil
 }
 
+// NewROBlockSlice is a helper method for converting a slice of the ReadOnlySignedBeaconBlock interface
+// to a slice of ROBlock.
+func NewROBlockSlice(blks []interfaces.ReadOnlySignedBeaconBlock) ([]ROBlock, error) {
+	robs := make([]ROBlock, len(blks))
+	var err error
+	for i := range blks {
+		robs[i], err = NewROBlock(blks[i])
+		if err != nil {
+			return nil, err
+		}
+	}
+	return robs, nil
+}
+
 // ROBlockSlice implements sort.Interface so that slices of ROBlocks can be easily sorted.
 // A slice of ROBlock is sorted first by slot, with ties broken by cached block roots.
 type ROBlockSlice []ROBlock

hack/update-go-pbs.sh

@@ -18,8 +18,8 @@ searchstring="prysmaticlabs/prysm/v4/"
 for ((i = 0; i < arraylength; i++)); do
     color "34" "$destination"
     destination=${file_list[i]#*$searchstring}
-    chmod 755 "$destination"
     cp -R -L "${file_list[i]}" "$destination"
+    chmod 755 "$destination"
 done
 
 # Run goimports on newly generated protos

proto/dbval/BUILD.bazel

@@ -0,0 +1,23 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+load("@rules_proto//proto:defs.bzl", "proto_library")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+proto_library(
+    name = "dbval_proto",
+    srcs = ["dbval.proto"],
+    visibility = ["//visibility:public"],
+)
+
+go_proto_library(
+    name = "dbval_go_proto",
+    importpath = "github.com/prysmaticlabs/prysm/v4/proto/dbval",
+    proto = ":dbval_proto",
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "go_default_library",
+    embed = [":dbval_go_proto"],
+    importpath = "github.com/prysmaticlabs/prysm/v4/proto/dbval",
+    visibility = ["//visibility:public"],
+)

proto/dbval/dbval.pb.go

@@ -0,0 +1,187 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.30.0
+// 	protoc        v4.23.3
+// source: proto/dbval/dbval.proto
+
+package dbval
+
+import (
+	reflect "reflect"
+	sync "sync"
+
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type BackfillStatus struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	LowSlot       uint64 `protobuf:"varint,1,opt,name=low_slot,json=lowSlot,proto3" json:"low_slot,omitempty"`
+	LowRoot       []byte `protobuf:"bytes,2,opt,name=low_root,json=lowRoot,proto3" json:"low_root,omitempty"`
+	LowParentRoot []byte `protobuf:"bytes,3,opt,name=low_parent_root,json=lowParentRoot,proto3" json:"low_parent_root,omitempty"`
+	OriginSlot    uint64 `protobuf:"varint,4,opt,name=origin_slot,json=originSlot,proto3" json:"origin_slot,omitempty"`
+	OriginRoot    []byte `protobuf:"bytes,6,opt,name=origin_root,json=originRoot,proto3" json:"origin_root,omitempty"`
+}
+
+func (x *BackfillStatus) Reset() {
+	*x = BackfillStatus{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_proto_dbval_dbval_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *BackfillStatus) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*BackfillStatus) ProtoMessage() {}
+
+func (x *BackfillStatus) ProtoReflect() protoreflect.Message {
+	mi := &file_proto_dbval_dbval_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use BackfillStatus.ProtoReflect.Descriptor instead.
+func (*BackfillStatus) Descriptor() ([]byte, []int) {
+	return file_proto_dbval_dbval_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *BackfillStatus) GetLowSlot() uint64 {
+	if x != nil {
+		return x.LowSlot
+	}
+	return 0
+}
+
+func (x *BackfillStatus) GetLowRoot() []byte {
+	if x != nil {
+		return x.LowRoot
+	}
+	return nil
+}
+
+func (x *BackfillStatus) GetLowParentRoot() []byte {
+	if x != nil {
+		return x.LowParentRoot
+	}
+	return nil
+}
+
+func (x *BackfillStatus) GetOriginSlot() uint64 {
+	if x != nil {
+		return x.OriginSlot
+	}
+	return 0
+}
+
+func (x *BackfillStatus) GetOriginRoot() []byte {
+	if x != nil {
+		return x.OriginRoot
+	}
+	return nil
+}
+
+var File_proto_dbval_dbval_proto protoreflect.FileDescriptor
+
+var file_proto_dbval_dbval_proto_rawDesc = []byte{
+	0x0a, 0x17, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x2f, 0x64, 0x62, 0x76, 0x61, 0x6c, 0x2f, 0x64, 0x62,
+	0x76, 0x61, 0x6c, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x12, 0x65, 0x74, 0x68, 0x65, 0x72,
+	0x65, 0x75, 0x6d, 0x2e, 0x65, 0x74, 0x68, 0x2e, 0x64, 0x62, 0x76, 0x61, 0x6c, 0x22, 0xb0, 0x01,
+	0x0a, 0x0e, 0x42, 0x61, 0x63, 0x6b, 0x66, 0x69, 0x6c, 0x6c, 0x53, 0x74, 0x61, 0x74, 0x75, 0x73,
+	0x12, 0x19, 0x0a, 0x08, 0x6c, 0x6f, 0x77, 0x5f, 0x73, 0x6c, 0x6f, 0x74, 0x18, 0x01, 0x20, 0x01,
+	0x28, 0x04, 0x52, 0x07, 0x6c, 0x6f, 0x77, 0x53, 0x6c, 0x6f, 0x74, 0x12, 0x19, 0x0a, 0x08, 0x6c,
+	0x6f, 0x77, 0x5f, 0x72, 0x6f, 0x6f, 0x74, 0x18, 0x02, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x07, 0x6c,
+	0x6f, 0x77, 0x52, 0x6f, 0x6f, 0x74, 0x12, 0x26, 0x0a, 0x0f, 0x6c, 0x6f, 0x77, 0x5f, 0x70, 0x61,
+	0x72, 0x65, 0x6e, 0x74, 0x5f, 0x72, 0x6f, 0x6f, 0x74, 0x18, 0x03, 0x20, 0x01, 0x28, 0x0c, 0x52,
+	0x0d, 0x6c, 0x6f, 0x77, 0x50, 0x61, 0x72, 0x65, 0x6e, 0x74, 0x52, 0x6f, 0x6f, 0x74, 0x12, 0x1f,
+	0x0a, 0x0b, 0x6f, 0x72, 0x69, 0x67, 0x69, 0x6e, 0x5f, 0x73, 0x6c, 0x6f, 0x74, 0x18, 0x04, 0x20,
+	0x01, 0x28, 0x04, 0x52, 0x0a, 0x6f, 0x72, 0x69, 0x67, 0x69, 0x6e, 0x53, 0x6c, 0x6f, 0x74, 0x12,
+	0x1f, 0x0a, 0x0b, 0x6f, 0x72, 0x69, 0x67, 0x69, 0x6e, 0x5f, 0x72, 0x6f, 0x6f, 0x74, 0x18, 0x06,
+	0x20, 0x01, 0x28, 0x0c, 0x52, 0x0a, 0x6f, 0x72, 0x69, 0x67, 0x69, 0x6e, 0x52, 0x6f, 0x6f, 0x74,
+	0x42, 0x35, 0x5a, 0x33, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x70,
+	0x72, 0x79, 0x73, 0x6d, 0x61, 0x74, 0x69, 0x63, 0x6c, 0x61, 0x62, 0x73, 0x2f, 0x70, 0x72, 0x79,
+	0x73, 0x6d, 0x2f, 0x76, 0x34, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x2f, 0x64, 0x62, 0x76, 0x61,
+	0x6c, 0x3b, 0x64, 0x62, 0x76, 0x61, 0x6c, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_proto_dbval_dbval_proto_rawDescOnce sync.Once
+	file_proto_dbval_dbval_proto_rawDescData = file_proto_dbval_dbval_proto_rawDesc
+)
+
+func file_proto_dbval_dbval_proto_rawDescGZIP() []byte {
+	file_proto_dbval_dbval_proto_rawDescOnce.Do(func() {
+		file_proto_dbval_dbval_proto_rawDescData = protoimpl.X.CompressGZIP(file_proto_dbval_dbval_proto_rawDescData)
+	})
+	return file_proto_dbval_dbval_proto_rawDescData
+}
+
+var file_proto_dbval_dbval_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_proto_dbval_dbval_proto_goTypes = []interface{}{
+	(*BackfillStatus)(nil), // 0: ethereum.eth.dbval.BackfillStatus
+}
+var file_proto_dbval_dbval_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_proto_dbval_dbval_proto_init() }
+func file_proto_dbval_dbval_proto_init() {
+	if File_proto_dbval_dbval_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_proto_dbval_dbval_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*BackfillStatus); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_proto_dbval_dbval_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_proto_dbval_dbval_proto_goTypes,
+		DependencyIndexes: file_proto_dbval_dbval_proto_depIdxs,
+		MessageInfos:      file_proto_dbval_dbval_proto_msgTypes,
+	}.Build()
+	File_proto_dbval_dbval_proto = out.File
+	file_proto_dbval_dbval_proto_rawDesc = nil
+	file_proto_dbval_dbval_proto_goTypes = nil
+	file_proto_dbval_dbval_proto_depIdxs = nil
+}

proto/dbval/dbval.proto

@@ -0,0 +1,23 @@
+syntax = "proto3";
+
+package ethereum.eth.dbval;
+
+option go_package = "github.com/prysmaticlabs/prysm/v4/proto/dbval;dbval";
+
+// BackfillStatus is a value used to keep track of the progress of the process of backfilling blocks leading up to
+// the origin block used to checkpoint sync a node. There is only one BackfillStatus value in the database.
+message BackfillStatus {
+    // low_slot is the slot of the last block that backfill will attempt to download and import.
+    // This is determined by MIN_EPOCHS_FOR_BLOCK_REQUESTS, or by a user-specified override.
+    uint64 low_slot = 1;
+    // low_root is the root of the last block that backfill will attempt to download and import.
+    bytes low_root = 2;
+    // low_parent_root is the parent_root of the block at low_root. This enables the backfill service to check
+    // that a block is the direct ancestor of the block for low_root without an additional db lookup.
+    bytes low_parent_root = 3;
+    // origin_slot is the slot of the origin block, which is the block used to initiate a checkpoint sync.
+    // Backfill uses the origin block as the reference point to determine canonical ancestors.
+    uint64 origin_slot = 4;
+    // origin_root is the root of the origin block.
+    bytes origin_root = 6;
+}

testing/assertions/assertions.go

@@ -169,19 +169,28 @@ func ErrorContains(loggerFn assertionLoggerFn, want string, err error, msg ...in
 
 // NotNil asserts that passed value is not nil.
 func NotNil(loggerFn assertionLoggerFn, obj interface{}, msg ...interface{}) {
-	if isNil(obj) {
+	if deepNil(obj) {
 		errMsg := parseMsg("Unexpected nil value", msg...)
 		_, file, line, _ := runtime.Caller(2)
 		loggerFn("%s:%d %s", filepath.Base(file), line, errMsg)
 	}
 }
 
-// isNil checks that underlying value of obj is nil.
-func isNil(obj interface{}) bool {
-	if obj == nil {
+// IsNil asserts that observed value is nil.
+func IsNil(loggerFn assertionLoggerFn, got interface{}, msg ...interface{}) {
+	if !deepNil(got) {
+		errMsg := parseMsg("Value is unexpectedly not nil", msg...)
+		_, file, line, _ := runtime.Caller(2)
+		loggerFn("%s:%d %s", filepath.Base(file), line, errMsg)
+	}
+}
+
+// deepNil checks that underlying value of obj is nil.
+func deepNil(got interface{}) bool {
+	if got == nil {
 		return true
 	}
-	value := reflect.ValueOf(obj)
+	value := reflect.ValueOf(got)
 	switch value.Kind() {
 	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
 		return value.IsNil()

testing/require/requires.go

@@ -51,6 +51,11 @@ func ErrorContains(tb assertions.AssertionTestingTB, want string, err error, msg
 	assertions.ErrorContains(tb.Fatalf, want, err, msg...)
 }
 
+// IsNil asserts that the observed value is nil.
+func IsNil(tb assertions.AssertionTestingTB, got interface{}, msg ...interface{}) {
+	assertions.IsNil(tb.Fatalf, got, msg...)
+}
+
 // NotNil asserts that passed value is not nil.
 func NotNil(tb assertions.AssertionTestingTB, obj interface{}, msg ...interface{}) {
 	assertions.NotNil(tb.Fatalf, obj, msg...)

testing/util/deneb.go

@@ -30,17 +30,15 @@ type denebBlockGenerator struct {
 	nblobs   int
 	sign     bool
 	sk       bls.SecretKey
-	pk       bls.PublicKey
 	proposer primitives.ValidatorIndex
 	valRoot  []byte
 }
 
-func WithProposerSigning(idx primitives.ValidatorIndex, sk bls.SecretKey, pk bls.PublicKey, valRoot []byte) DenebBlockGeneratorOption {
+func WithProposerSigning(idx primitives.ValidatorIndex, sk bls.SecretKey, valRoot []byte) DenebBlockGeneratorOption {
 	return func(g *denebBlockGenerator) {
 		g.sign = true
 		g.proposer = idx
 		g.sk = sk
-		g.pk = pk
 		g.valRoot = valRoot
 	}
 }
@@ -97,6 +95,7 @@ func GenerateTestDenebBlockWithSidecar(t *testing.T, parent [32]byte, slot primi
 	block.Block.Body.ExecutionPayload = payload
 	block.Block.Slot = g.slot
 	block.Block.ParentRoot = g.parent[:]
+	block.Block.ProposerIndex = g.proposer
 	commitments := make([][48]byte, g.nblobs)
 	block.Block.Body.BlobKzgCommitments = make([][]byte, g.nblobs)
 	for i := range commitments {

time/slots/slottime.go

@@ -98,6 +98,16 @@ func EpochStart(epoch primitives.Epoch) (primitives.Slot, error) {
 	return slot, nil
 }
 
+// UnsafeEpochStart is a version of EpochStart that panics if there is an overflow. It can be safely used by code
+// that first guarantees epoch <= MaxSafeEpoch.
+func UnsafeEpochStart(epoch primitives.Epoch) primitives.Slot {
+	es, err := EpochStart(epoch)
+	if err != nil {
+		panic(err)
+	}
+	return es
+}
+
 // EpochEnd returns the last slot number of the
 // current epoch.
 func EpochEnd(epoch primitives.Epoch) (primitives.Slot, error) {
@@ -271,3 +281,8 @@ func WithinVotingWindow(genesisTime uint64, slot primitives.Slot) bool {
 	votingWindow := params.BeaconConfig().SecondsPerSlot / params.BeaconConfig().IntervalsPerSlot
 	return time.Since(StartTime(genesisTime, slot)) < time.Duration(votingWindow)*time.Second
 }
+
+// MaxSafeEpoch gives the largest epoch value that can be safely converted to a slot.
+func MaxSafeEpoch() primitives.Epoch {
+	return primitives.Epoch(math.MaxUint64 / uint64(params.BeaconConfig().SlotsPerEpoch))
+}