core, ethdb, tests, trie: introduce database snapshot (ethereum#24486)

core/rawdb/table.go

@@ -177,6 +177,13 @@ func (t *table) NewBatchWithSize(size int) ethdb.Batch {
 	return &tableBatch{t.db.NewBatchWithSize(size), t.prefix}
 }
 
+// NewSnapshot creates a database snapshot based on the current state.
+// The created snapshot will not be affected by all following mutations
+// happened on the database.
+func (t *table) NewSnapshot() (ethdb.Snapshot, error) {
+	return t.db.NewSnapshot()
+}
+
 // tableBatch is a wrapper around a database batch that prefixes each key access
 // with a pre-configured string.
 type tableBatch struct {

ethdb/database.go

@@ -64,6 +64,7 @@ type KeyValueStore interface {
 	Iteratee
 	Stater
 	Compacter
+	Snapshotter
 	io.Closer
 }
 
@@ -153,5 +154,6 @@ type Database interface {
 	Iteratee
 	Stater
 	Compacter
+	Snapshotter
 	io.Closer
 }

ethdb/dbtest/testsuite.go

@@ -313,6 +313,68 @@ func TestDatabaseSuite(t *testing.T, New func() ethdb.KeyValueStore) {
 		}
 	})
 
+	t.Run("Snapshot", func(t *testing.T) {
+		db := New()
+		defer db.Close()
+
+		initial := map[string]string{
+			"k1": "v1", "k2": "v2", "k3": "", "k4": "",
+		}
+		for k, v := range initial {
+			db.Put([]byte(k), []byte(v))
+		}
+		snapshot, err := db.NewSnapshot()
+		if err != nil {
+			t.Fatal(err)
+		}
+		for k, v := range initial {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !bytes.Equal(got, []byte(v)) {
+				t.Fatalf("Unexpected value want: %v, got %v", v, got)
+			}
+		}
+
+		// Flush more modifications into the database, ensure the snapshot
+		// isn't affected.
+		var (
+			update = map[string]string{"k1": "v1-b", "k3": "v3-b"}
+			insert = map[string]string{"k5": "v5-b"}
+			delete = map[string]string{"k2": ""}
+		)
+		for k, v := range update {
+			db.Put([]byte(k), []byte(v))
+		}
+		for k, v := range insert {
+			db.Put([]byte(k), []byte(v))
+		}
+		for k := range delete {
+			db.Delete([]byte(k))
+		}
+		for k, v := range initial {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !bytes.Equal(got, []byte(v)) {
+				t.Fatalf("Unexpected value want: %v, got %v", v, got)
+			}
+		}
+		for k := range insert {
+			got, err := snapshot.Get([]byte(k))
+			if err == nil || len(got) != 0 {
+				t.Fatal("Unexpected value")
+			}
+		}
+		for k := range delete {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil || len(got) == 0 {
+				t.Fatal("Unexpected deletion")
+			}
+		}
+	})
 }
 
 func iterateKeys(it ethdb.Iterator) []string {

ethdb/leveldb/leveldb.go

@@ -228,6 +228,19 @@ func (db *Database) NewIterator(prefix []byte, start []byte) ethdb.Iterator {
 	return db.db.NewIterator(bytesPrefixRange(prefix, start), nil)
 }
 
+// NewSnapshot creates a database snapshot based on the current state.
+// The created snapshot will not be affected by all following mutations
+// happened on the database.
+// Note don't forget to release the snapshot once it's used up, otherwise
+// the stale data will never be cleaned up by the underlying compactor.
+func (db *Database) NewSnapshot() (ethdb.Snapshot, error) {
+	snap, err := db.db.GetSnapshot()
+	if err != nil {
+		return nil, err
+	}
+	return &snapshot{db: snap}, nil
+}
+
 // Stat returns a particular internal stat of the database.
 func (db *Database) Stat(property string) (string, error) {
 	return db.db.GetProperty(property)
@@ -527,3 +540,26 @@ func bytesPrefixRange(prefix, start []byte) *util.Range {
 	r.Start = append(r.Start, start...)
 	return r
 }
+
+// snapshot wraps a leveldb snapshot for implementing the Snapshot interface.
+type snapshot struct {
+	db *leveldb.Snapshot
+}
+
+// Has retrieves if a key is present in the snapshot backing by a key-value
+// data store.
+func (snap *snapshot) Has(key []byte) (bool, error) {
+	return snap.db.Has(key, nil)
+}
+
+// Get retrieves the given key if it's present in the snapshot backing by
+// key-value data store.
+func (snap *snapshot) Get(key []byte) ([]byte, error) {
+	return snap.db.Get(key, nil)
+}
+
+// Release releases associated resources. Release should always succeed and can
+// be called multiple times without causing error.
+func (snap *snapshot) Release() {
+	snap.db.Release()
+}

ethdb/memorydb/memorydb.go

@@ -35,6 +35,10 @@ var (
 	// errMemorydbNotFound is returned if a key is requested that is not found in
 	// the provided memory database.
 	errMemorydbNotFound = errors.New("not found")
+
+	// errSnapshotReleased is returned if callers want to retrieve data from a
+	// released snapshot.
+	errSnapshotReleased = errors.New("snapshot released")
 )
 
 // Database is an ephemeral key-value store. Apart from basic data storage
@@ -53,7 +57,7 @@ func New() *Database {
 	}
 }
 
-// NewWithCap returns a wrapped map pre-allocated to the provided capcity with
+// NewWithCap returns a wrapped map pre-allocated to the provided capacity with
 // all the required database interface methods implemented.
 func NewWithCap(size int) *Database {
 	return &Database{
@@ -170,6 +174,13 @@ func (db *Database) NewIterator(prefix []byte, start []byte) ethdb.Iterator {
 	}
 }
 
+// NewSnapshot creates a database snapshot based on the current state.
+// The created snapshot will not be affected by all following mutations
+// happened on the database.
+func (db *Database) NewSnapshot() (ethdb.Snapshot, error) {
+	return newSnapshot(db), nil
+}
+
 // Stat returns a particular internal stat of the database.
 func (db *Database) Stat(property string) (string, error) {
 	return "", errors.New("unknown property")
@@ -320,3 +331,59 @@ func (it *iterator) Value() []byte {
 func (it *iterator) Release() {
 	it.keys, it.values = nil, nil
 }
+
+// snapshot wraps a batch of key-value entries deep copied from the in-memory
+// database for implementing the Snapshot interface.
+type snapshot struct {
+	db   map[string][]byte
+	lock sync.RWMutex
+}
+
+// newSnapshot initializes the snapshot with the given database instance.
+func newSnapshot(db *Database) *snapshot {
+	db.lock.RLock()
+	defer db.lock.RUnlock()
+
+	copied := make(map[string][]byte)
+	for key, val := range db.db {
+		copied[key] = common.CopyBytes(val)
+	}
+	return &snapshot{db: copied}
+}
+
+// Has retrieves if a key is present in the snapshot backing by a key-value
+// data store.
+func (snap *snapshot) Has(key []byte) (bool, error) {
+	snap.lock.RLock()
+	defer snap.lock.RUnlock()
+
+	if snap.db == nil {
+		return false, errSnapshotReleased
+	}
+	_, ok := snap.db[string(key)]
+	return ok, nil
+}
+
+// Get retrieves the given key if it's present in the snapshot backing by
+// key-value data store.
+func (snap *snapshot) Get(key []byte) ([]byte, error) {
+	snap.lock.RLock()
+	defer snap.lock.RUnlock()
+
+	if snap.db == nil {
+		return nil, errSnapshotReleased
+	}
+	if entry, ok := snap.db[string(key)]; ok {
+		return common.CopyBytes(entry), nil
+	}
+	return nil, errMemorydbNotFound
+}
+
+// Release releases associated resources. Release should always succeed and can
+// be called multiple times without causing error.
+func (snap *snapshot) Release() {
+	snap.lock.Lock()
+	defer snap.lock.Unlock()
+
+	snap.db = nil
+}

ethdb/snapshot.go

@@ -0,0 +1,41 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethdb
+
+type Snapshot interface {
+	// Has retrieves if a key is present in the snapshot backing by a key-value
+	// data store.
+	Has(key []byte) (bool, error)
+
+	// Get retrieves the given key if it's present in the snapshot backing by
+	// key-value data store.
+	Get(key []byte) ([]byte, error)
+
+	// Release releases associated resources. Release should always succeed and can
+	// be called multiple times without causing error.
+	Release()
+}
+
+// Snapshotter wraps the Snapshot method of a backing data store.
+type Snapshotter interface {
+	// NewSnapshot creates a database snapshot based on the current state.
+	// The created snapshot will not be affected by all following mutations
+	// happened on the database.
+	// Note don't forget to release the snapshot once it's used up, otherwise
+	// the stale data will never be cleaned up by the underlying compactor.
+	NewSnapshot() (Snapshot, error)
+}

tests/fuzzers/stacktrie/trie_fuzzer.go

@@ -67,6 +67,7 @@ func (s *spongeDb) Get(key []byte) ([]byte, error)           { return nil, error
 func (s *spongeDb) Delete(key []byte) error                  { panic("implement me") }
 func (s *spongeDb) NewBatch() ethdb.Batch                    { return &spongeBatch{s} }
 func (s *spongeDb) NewBatchWithSize(size int) ethdb.Batch    { return &spongeBatch{s} }
+func (s *spongeDb) NewSnapshot() (ethdb.Snapshot, error)     { panic("implement me") }
 func (s *spongeDb) Stat(property string) (string, error)     { panic("implement me") }
 func (s *spongeDb) Compact(start []byte, limit []byte) error { panic("implement me") }
 func (s *spongeDb) Close() error                             { return nil }

trie/iterator_test.go

@@ -475,9 +475,13 @@ func (l *loggingDb) NewBatchWithSize(size int) ethdb.Batch {
 }
 
 func (l *loggingDb) NewIterator(prefix []byte, start []byte) ethdb.Iterator {
-	fmt.Printf("NewIterator\n")
 	return l.backend.NewIterator(prefix, start)
 }
+
+func (l *loggingDb) NewSnapshot() (ethdb.Snapshot, error) {
+	return l.backend.NewSnapshot()
+}
+
 func (l *loggingDb) Stat(property string) (string, error) {
 	return l.backend.Stat(property)
 }

trie/trie_test.go

@@ -677,6 +677,7 @@ func (s *spongeDb) Get(key []byte) ([]byte, error)           { return nil, error
 func (s *spongeDb) Delete(key []byte) error                  { panic("implement me") }
 func (s *spongeDb) NewBatch() ethdb.Batch                    { return &spongeBatch{s} }
 func (s *spongeDb) NewBatchWithSize(size int) ethdb.Batch    { return &spongeBatch{s} }
+func (s *spongeDb) NewSnapshot() (ethdb.Snapshot, error)     { panic("implement me") }
 func (s *spongeDb) Stat(property string) (string, error)     { panic("implement me") }
 func (s *spongeDb) Compact(start []byte, limit []byte) error { panic("implement me") }
 func (s *spongeDb) Close() error                             { return nil }