core/rawdb, ethdb: introduce batched/atomic reads from ancients (#23566)

This PR adds a new accessor method to the freezer database. This new view offers a consistent interface, guaranteeing that all individual tables (headers, bodies etc) are all on the same number, and that this number is not changes (added/truncated) while the operation is performing.

core/rawdb/accessors_chain.go

@@ -35,20 +35,15 @@ import (
 
 // ReadCanonicalHash retrieves the hash assigned to a canonical block number.
 func ReadCanonicalHash(db ethdb.Reader, number uint64) common.Hash {
-	data, _ := db.Ancient(freezerHashTable, number)
+	var data []byte
-	if len(data) == 0 {
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-		data, _ = db.Get(headerHashKey(number))
+		data, _ = reader.Ancient(freezerHashTable, number)
-		// In the background freezer is moving data from leveldb to flatten files.
-		// So during the first check for ancient db, the data is not yet in there,
-		// but when we reach into leveldb, the data was already moved. That would
-		// result in a not found error.
 		if len(data) == 0 {
-			data, _ = db.Ancient(freezerHashTable, number)
+			// Get it by hash from leveldb
+			data, _ = db.Get(headerHashKey(number))
 		}
-	}
+		return nil
-	if len(data) == 0 {
+	})
-		return common.Hash{}
-	}
 	return common.BytesToHash(data)
 }
 
@@ -304,32 +299,25 @@ func WriteFastTxLookupLimit(db ethdb.KeyValueWriter, number uint64) {
 
 // ReadHeaderRLP retrieves a block header in its raw RLP database encoding.
 func ReadHeaderRLP(db ethdb.Reader, hash common.Hash, number uint64) rlp.RawValue {
-	// First try to look up the data in ancient database. Extra hash
+	var data []byte
-	// comparison is necessary since ancient database only maintains
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-	// the canonical data.
+		// First try to look up the data in ancient database. Extra hash
-	data, _ := db.Ancient(freezerHeaderTable, number)
+		// comparison is necessary since ancient database only maintains
-	if len(data) > 0 && crypto.Keccak256Hash(data) == hash {
+		// the canonical data.
-		return data
+		data, _ = reader.Ancient(freezerHeaderTable, number)
-	}
+		if len(data) > 0 && crypto.Keccak256Hash(data) == hash {
-	// Then try to look up the data in leveldb.
+			return nil
-	data, _ = db.Get(headerKey(number, hash))
+		}
-	if len(data) > 0 {
+		// If not, try reading from leveldb
-		return data
+		data, _ = db.Get(headerKey(number, hash))
-	}
+		return nil
-	// In the background freezer is moving data from leveldb to flatten files.
+	})
-	// So during the first check for ancient db, the data is not yet in there,
+	return data
-	// but when we reach into leveldb, the data was already moved. That would
-	// result in a not found error.
-	data, _ = db.Ancient(freezerHeaderTable, number)
-	if len(data) > 0 && crypto.Keccak256Hash(data) == hash {
-		return data
-	}
-	return nil // Can't find the data anywhere.
 }
 
 // HasHeader verifies the existence of a block header corresponding to the hash.
 func HasHeader(db ethdb.Reader, hash common.Hash, number uint64) bool {
-	if has, err := db.Ancient(freezerHashTable, number); err == nil && common.BytesToHash(has) == hash {
+	if isCanon(db, number, hash) {
 		return true
 	}
 	if has, err := db.Has(headerKey(number, hash)); !has || err != nil {
@@ -389,53 +377,48 @@ func deleteHeaderWithoutNumber(db ethdb.KeyValueWriter, hash common.Hash, number
 	}
 }
 
+// isCanon is an internal utility method, to check whether the given number/hash
+// is part of the ancient (canon) set.
+func isCanon(reader ethdb.AncientReader, number uint64, hash common.Hash) bool {
+	h, err := reader.Ancient(freezerHashTable, number)
+	if err != nil {
+		return false
+	}
+	return bytes.Equal(h, hash[:])
+}
+
 // ReadBodyRLP retrieves the block body (transactions and uncles) in RLP encoding.
 func ReadBodyRLP(db ethdb.Reader, hash common.Hash, number uint64) rlp.RawValue {
 	// First try to look up the data in ancient database. Extra hash
 	// comparison is necessary since ancient database only maintains
 	// the canonical data.
-	data, _ := db.Ancient(freezerBodiesTable, number)
+	var data []byte
-	if len(data) > 0 {
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-		h, _ := db.Ancient(freezerHashTable, number)
+		// Check if the data is in ancients
-		if common.BytesToHash(h) == hash {
+		if isCanon(reader, number, hash) {
-			return data
+			data, _ = reader.Ancient(freezerBodiesTable, number)
+			return nil
 		}
-	}
+		// If not, try reading from leveldb
-	// Then try to look up the data in leveldb.
+		data, _ = db.Get(blockBodyKey(number, hash))
-	data, _ = db.Get(blockBodyKey(number, hash))
+		return nil
-	if len(data) > 0 {
+	})
-		return data
+	return data
-	}
-	// In the background freezer is moving data from leveldb to flatten files.
-	// So during the first check for ancient db, the data is not yet in there,
-	// but when we reach into leveldb, the data was already moved. That would
-	// result in a not found error.
-	data, _ = db.Ancient(freezerBodiesTable, number)
-	if len(data) > 0 {
-		h, _ := db.Ancient(freezerHashTable, number)
-		if common.BytesToHash(h) == hash {
-			return data
-		}
-	}
-	return nil // Can't find the data anywhere.
 }
 
 // ReadCanonicalBodyRLP retrieves the block body (transactions and uncles) for the canonical
 // block at number, in RLP encoding.
 func ReadCanonicalBodyRLP(db ethdb.Reader, number uint64) rlp.RawValue {
-	// If it's an ancient one, we don't need the canonical hash
+	var data []byte
-	data, _ := db.Ancient(freezerBodiesTable, number)
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-	if len(data) == 0 {
+		data, _ = reader.Ancient(freezerBodiesTable, number)
-		// Need to get the hash
+		if len(data) > 0 {
-		data, _ = db.Get(blockBodyKey(number, ReadCanonicalHash(db, number)))
+			return nil
-		// In the background freezer is moving data from leveldb to flatten files.
-		// So during the first check for ancient db, the data is not yet in there,
-		// but when we reach into leveldb, the data was already moved. That would
-		// result in a not found error.
-		if len(data) == 0 {
-			data, _ = db.Ancient(freezerBodiesTable, number)
 		}
-	}
+		// Get it by hash from leveldb
+		data, _ = db.Get(blockBodyKey(number, ReadCanonicalHash(db, number)))
+		return nil
+	})
 	return data
 }
 
@@ -448,7 +431,7 @@ func WriteBodyRLP(db ethdb.KeyValueWriter, hash common.Hash, number uint64, rlp
 
 // HasBody verifies the existence of a block body corresponding to the hash.
 func HasBody(db ethdb.Reader, hash common.Hash, number uint64) bool {
-	if has, err := db.Ancient(freezerHashTable, number); err == nil && common.BytesToHash(has) == hash {
+	if isCanon(db, number, hash) {
 		return true
 	}
 	if has, err := db.Has(blockBodyKey(number, hash)); !has || err != nil {
@@ -489,33 +472,18 @@ func DeleteBody(db ethdb.KeyValueWriter, hash common.Hash, number uint64) {
 
 // ReadTdRLP retrieves a block's total difficulty corresponding to the hash in RLP encoding.
 func ReadTdRLP(db ethdb.Reader, hash common.Hash, number uint64) rlp.RawValue {
-	// First try to look up the data in ancient database. Extra hash
+	var data []byte
-	// comparison is necessary since ancient database only maintains
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-	// the canonical data.
+		// Check if the data is in ancients
-	data, _ := db.Ancient(freezerDifficultyTable, number)
+		if isCanon(reader, number, hash) {
-	if len(data) > 0 {
+			data, _ = reader.Ancient(freezerDifficultyTable, number)
-		h, _ := db.Ancient(freezerHashTable, number)
+			return nil
-		if common.BytesToHash(h) == hash {
-			return data
 		}
-	}
+		// If not, try reading from leveldb
-	// Then try to look up the data in leveldb.
+		data, _ = db.Get(headerTDKey(number, hash))
-	data, _ = db.Get(headerTDKey(number, hash))
+		return nil
-	if len(data) > 0 {
+	})
-		return data
+	return data
-	}
-	// In the background freezer is moving data from leveldb to flatten files.
-	// So during the first check for ancient db, the data is not yet in there,
-	// but when we reach into leveldb, the data was already moved. That would
-	// result in a not found error.
-	data, _ = db.Ancient(freezerDifficultyTable, number)
-	if len(data) > 0 {
-		h, _ := db.Ancient(freezerHashTable, number)
-		if common.BytesToHash(h) == hash {
-			return data
-		}
-	}
-	return nil // Can't find the data anywhere.
 }
 
 // ReadTd retrieves a block's total difficulty corresponding to the hash.
@@ -553,7 +521,7 @@ func DeleteTd(db ethdb.KeyValueWriter, hash common.Hash, number uint64) {
 // HasReceipts verifies the existence of all the transaction receipts belonging
 // to a block.
 func HasReceipts(db ethdb.Reader, hash common.Hash, number uint64) bool {
-	if has, err := db.Ancient(freezerHashTable, number); err == nil && common.BytesToHash(has) == hash {
+	if isCanon(db, number, hash) {
 		return true
 	}
 	if has, err := db.Has(blockReceiptsKey(number, hash)); !has || err != nil {
@@ -564,33 +532,18 @@ func HasReceipts(db ethdb.Reader, hash common.Hash, number uint64) bool {
 
 // ReadReceiptsRLP retrieves all the transaction receipts belonging to a block in RLP encoding.
 func ReadReceiptsRLP(db ethdb.Reader, hash common.Hash, number uint64) rlp.RawValue {
-	// First try to look up the data in ancient database. Extra hash
+	var data []byte
-	// comparison is necessary since ancient database only maintains
+	db.ReadAncients(func(reader ethdb.AncientReader) error {
-	// the canonical data.
+		// Check if the data is in ancients
-	data, _ := db.Ancient(freezerReceiptTable, number)
+		if isCanon(reader, number, hash) {
-	if len(data) > 0 {
+			data, _ = reader.Ancient(freezerReceiptTable, number)
-		h, _ := db.Ancient(freezerHashTable, number)
+			return nil
-		if common.BytesToHash(h) == hash {
-			return data
 		}
-	}
+		// If not, try reading from leveldb
-	// Then try to look up the data in leveldb.
+		data, _ = db.Get(blockReceiptsKey(number, hash))
-	data, _ = db.Get(blockReceiptsKey(number, hash))
+		return nil
-	if len(data) > 0 {
+	})
-		return data
+	return data
-	}
-	// In the background freezer is moving data from leveldb to flatten files.
-	// So during the first check for ancient db, the data is not yet in there,
-	// but when we reach into leveldb, the data was already moved. That would
-	// result in a not found error.
-	data, _ = db.Ancient(freezerReceiptTable, number)
-	if len(data) > 0 {
-		h, _ := db.Ancient(freezerHashTable, number)
-		if common.BytesToHash(h) == hash {
-			return data
-		}
-	}
-	return nil // Can't find the data anywhere.
 }
 
 // ReadRawReceipts retrieves all the transaction receipts belonging to a block.

core/rawdb/database.go

@@ -89,8 +89,8 @@ func (db *nofreezedb) Ancient(kind string, number uint64) ([]byte, error) {
 	return nil, errNotSupported
 }
 
-// ReadAncients returns an error as we don't have a backing chain freezer.
+// AncientRange returns an error as we don't have a backing chain freezer.
-func (db *nofreezedb) ReadAncients(kind string, start, max, maxByteSize uint64) ([][]byte, error) {
+func (db *nofreezedb) AncientRange(kind string, start, max, maxByteSize uint64) ([][]byte, error) {
 	return nil, errNotSupported
 }
 
@@ -119,6 +119,22 @@ func (db *nofreezedb) Sync() error {
 	return errNotSupported
 }
 
+func (db *nofreezedb) ReadAncients(fn func(reader ethdb.AncientReader) error) (err error) {
+	// Unlike other ancient-related methods, this method does not return
+	// errNotSupported when invoked.
+	// The reason for this is that the caller might want to do several things:
+	// 1. Check if something is in freezer,
+	// 2. If not, check leveldb.
+	//
+	// This will work, since the ancient-checks inside 'fn' will return errors,
+	// and the leveldb work will continue.
+	//
+	// If we instead were to return errNotSupported here, then the caller would
+	// have to explicitly check for that, having an extra clause to do the
+	// non-ancient operations.
+	return fn(db)
+}
+
 // NewDatabase creates a high level database on top of a given key-value data
 // store without a freezer moving immutable chain segments into cold storage.
 func NewDatabase(db ethdb.KeyValueStore) ethdb.Database {

core/rawdb/freezer.go

@@ -80,8 +80,9 @@ type freezer struct {
 	frozen    uint64 // Number of blocks already frozen
 	threshold uint64 // Number of recent blocks not to freeze (params.FullImmutabilityThreshold apart from tests)
 
-	// This lock synchronizes writers and the truncate operation.
+	// This lock synchronizes writers and the truncate operation, as well as
-	writeLock  sync.Mutex
+	// the "atomic" (batched) read operations.
+	writeLock  sync.RWMutex
 	writeBatch *freezerBatch
 
 	readonly     bool
@@ -201,12 +202,12 @@ func (f *freezer) Ancient(kind string, number uint64) ([]byte, error) {
 	return nil, errUnknownTable
 }
 
-// ReadAncients retrieves multiple items in sequence, starting from the index 'start'.
+// AncientRange retrieves multiple items in sequence, starting from the index 'start'.
 // It will return
 //  - at most 'max' items,
 //  - at least 1 item (even if exceeding the maxByteSize), but will otherwise
 //   return as many items as fit into maxByteSize.
-func (f *freezer) ReadAncients(kind string, start, count, maxBytes uint64) ([][]byte, error) {
+func (f *freezer) AncientRange(kind string, start, count, maxBytes uint64) ([][]byte, error) {
 	if table := f.tables[kind]; table != nil {
 		return table.RetrieveItems(start, count, maxBytes)
 	}
@@ -222,8 +223,8 @@ func (f *freezer) Ancients() (uint64, error) {
 func (f *freezer) AncientSize(kind string) (uint64, error) {
 	// This needs the write lock to avoid data races on table fields.
 	// Speed doesn't matter here, AncientSize is for debugging.
-	f.writeLock.Lock()
+	f.writeLock.RLock()
-	defer f.writeLock.Unlock()
+	defer f.writeLock.RUnlock()
 
 	if table := f.tables[kind]; table != nil {
 		return table.size()
@@ -231,6 +232,14 @@ func (f *freezer) AncientSize(kind string) (uint64, error) {
 	return 0, errUnknownTable
 }
 
+// ReadAncients runs the given read operation while ensuring that no writes take place
+// on the underlying freezer.
+func (f *freezer) ReadAncients(fn func(ethdb.AncientReader) error) (err error) {
+	f.writeLock.RLock()
+	defer f.writeLock.RUnlock()
+	return fn(f)
+}
+
 // ModifyAncients runs the given write operation.
 func (f *freezer) ModifyAncients(fn func(ethdb.AncientWriteOp) error) (writeSize int64, err error) {
 	if f.readonly {

core/rawdb/table.go

@@ -62,10 +62,10 @@ func (t *table) Ancient(kind string, number uint64) ([]byte, error) {
 	return t.db.Ancient(kind, number)
 }
 
-// ReadAncients is a noop passthrough that just forwards the request to the underlying
+// AncientRange is a noop passthrough that just forwards the request to the underlying
 // database.
-func (t *table) ReadAncients(kind string, start, count, maxBytes uint64) ([][]byte, error) {
+func (t *table) AncientRange(kind string, start, count, maxBytes uint64) ([][]byte, error) {
-	return t.db.ReadAncients(kind, start, count, maxBytes)
+	return t.db.AncientRange(kind, start, count, maxBytes)
 }
 
 // Ancients is a noop passthrough that just forwards the request to the underlying
@@ -85,6 +85,10 @@ func (t *table) ModifyAncients(fn func(ethdb.AncientWriteOp) error) (int64, erro
 	return t.db.ModifyAncients(fn)
 }
 
+func (t *table) ReadAncients(fn func(reader ethdb.AncientReader) error) (err error) {
+	return t.db.ReadAncients(fn)
+}
+
 // TruncateAncients is a noop passthrough that just forwards the request to the underlying
 // database.
 func (t *table) TruncateAncients(items uint64) error {

ethdb/database.go

@@ -76,12 +76,12 @@ type AncientReader interface {
 	// Ancient retrieves an ancient binary blob from the append-only immutable files.
 	Ancient(kind string, number uint64) ([]byte, error)
 
-	// ReadAncients retrieves multiple items in sequence, starting from the index 'start'.
+	// AncientRange retrieves multiple items in sequence, starting from the index 'start'.
 	// It will return
 	//  - at most 'count' items,
 	//  - at least 1 item (even if exceeding the maxBytes), but will otherwise
 	//   return as many items as fit into maxBytes.
-	ReadAncients(kind string, start, count, maxBytes uint64) ([][]byte, error)
+	AncientRange(kind string, start, count, maxBytes uint64) ([][]byte, error)
 
 	// Ancients returns the ancient item numbers in the ancient store.
 	Ancients() (uint64, error)
@@ -90,6 +90,15 @@ type AncientReader interface {
 	AncientSize(kind string) (uint64, error)
 }
 
+// AncientBatchReader is the interface for 'batched' or 'atomic' reading.
+type AncientBatchReader interface {
+	AncientReader
+
+	// ReadAncients runs the given read operation while ensuring that no writes take place
+	// on the underlying freezer.
+	ReadAncients(fn func(AncientReader) error) (err error)
+}
+
 // AncientWriter contains the methods required to write to immutable ancient data.
 type AncientWriter interface {
 	// ModifyAncients runs a write operation on the ancient store.
@@ -117,7 +126,7 @@ type AncientWriteOp interface {
 // immutable ancient data.
 type Reader interface {
 	KeyValueReader
-	AncientReader
+	AncientBatchReader
 }
 
 // Writer contains the methods required to write data to both key-value as well as
@@ -130,7 +139,7 @@ type Writer interface {
 // AncientStore contains all the methods required to allow handling different
 // ancient data stores backing immutable chain data store.
 type AncientStore interface {
-	AncientReader
+	AncientBatchReader
 	AncientWriter
 	io.Closer
 }