Abstract KVDB from StateDB

- KVDB contains the Checkpoint & Resets system
- StateDB uses KVDB and adds all the StateDB related methods

coordinator/purger.go

@@ -123,7 +123,7 @@ func poolMarkInvalidOldNonces(l2DB *l2db.L2DB, stateDB *statedb.LocalStateDB,
 		return tracerr.Wrap(err)
 	}
 	idxsNonce := make([]common.IdxNonce, len(idxs))
-	lastIdx, err := stateDB.GetIdx()
+	lastIdx, err := stateDB.GetCurrentIdx()
 	if err != nil {
 		return tracerr.Wrap(err)
 	}

db/kvdb/kvdb.go

@@ -0,0 +1,405 @@
+// Package kvdb provides a key-value database with Checkpoints & Resets system
+package kvdb
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"sort"
+	"strings"
+
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/hermeznetwork/hermez-node/log"
+	"github.com/hermeznetwork/tracerr"
+	"github.com/iden3/go-merkletree/db"
+	"github.com/iden3/go-merkletree/db/pebble"
+)
+
+const (
+	// PathBatchNum defines the subpath of the Batch Checkpoint in the
+	// subpath of the KVDB
+	PathBatchNum = "BatchNum"
+	// PathCurrent defines the subpath of the current Batch in the subpath
+	// of the KVDB
+	PathCurrent = "current"
+)
+
+var (
+	// KeyCurrentBatch is used as key in the db to store the current BatchNum
+	KeyCurrentBatch = []byte("k:currentbatch")
+	// keyCurrentIdx is used as key in the db to store the CurrentIdx
+	keyCurrentIdx = []byte("k:idx")
+)
+
+// KVDB represents the Key-Value DB object
+type KVDB struct {
+	path string
+	db   *pebble.Storage
+	// CurrentIdx holds the current Idx that the BatchBuilder is using
+	CurrentIdx   common.Idx
+	CurrentBatch common.BatchNum
+	keep         int
+}
+
+// NewKVDB creates a new KVDB, allowing to use an in-memory or in-disk storage.
+// Checkpoints older than the value defined by `keep` will be deleted.
+func NewKVDB(pathDB string, keep int) (*KVDB, error) {
+	var sto *pebble.Storage
+	var err error
+	sto, err = pebble.NewPebbleStorage(path.Join(pathDB, PathCurrent), false)
+	if err != nil {
+		return nil, tracerr.Wrap(err)
+	}
+
+	kvdb := &KVDB{
+		path: pathDB,
+		db:   sto,
+		keep: keep,
+	}
+	// load currentBatch
+	kvdb.CurrentBatch, err = kvdb.GetCurrentBatch()
+	if err != nil {
+		return nil, tracerr.Wrap(err)
+	}
+
+	// make reset (get checkpoint) at currentBatch
+	err = kvdb.reset(kvdb.CurrentBatch, false)
+	if err != nil {
+		return nil, tracerr.Wrap(err)
+	}
+
+	return kvdb, nil
+}
+
+// DB returns the *pebble.Storage from the KVDB
+func (kvdb *KVDB) DB() *pebble.Storage {
+	return kvdb.db
+}
+
+// StorageWithPrefix returns the db.Storage with the given prefix from the
+// current KVDB
+func (kvdb *KVDB) StorageWithPrefix(prefix []byte) db.Storage {
+	return kvdb.db.WithPrefix(prefix)
+}
+
+// Reset resets the KVDB to the checkpoint at the given batchNum. Reset does
+// not delete the checkpoints between old current and the new current, those
+// checkpoints will remain in the storage, and eventually will be deleted when
+// MakeCheckpoint overwrites them.
+func (kvdb *KVDB) Reset(batchNum common.BatchNum) error {
+	return kvdb.reset(batchNum, true)
+}
+
+// reset resets the KVDB to the checkpoint at the given batchNum. Reset does
+// not delete the checkpoints between old current and the new current, those
+// checkpoints will remain in the storage, and eventually will be deleted when
+// MakeCheckpoint overwrites them.  `closeCurrent` will close the currently
+// opened db before doing the reset.
+func (kvdb *KVDB) reset(batchNum common.BatchNum, closeCurrent bool) error {
+	currentPath := path.Join(kvdb.path, PathCurrent)
+
+	if closeCurrent {
+		if err := kvdb.db.Pebble().Close(); err != nil {
+			return tracerr.Wrap(err)
+		}
+	}
+	// remove 'current'
+	err := os.RemoveAll(currentPath)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	// remove all checkpoints > batchNum
+	for i := batchNum + 1; i <= kvdb.CurrentBatch; i++ {
+		if err := kvdb.DeleteCheckpoint(i); err != nil {
+			return tracerr.Wrap(err)
+		}
+	}
+	if batchNum == 0 {
+		// if batchNum == 0, open the new fresh 'current'
+		sto, err := pebble.NewPebbleStorage(currentPath, false)
+		if err != nil {
+			return tracerr.Wrap(err)
+		}
+		kvdb.db = sto
+		kvdb.CurrentIdx = 255
+		kvdb.CurrentBatch = batchNum
+
+		return nil
+	}
+
+	checkpointPath := path.Join(kvdb.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
+	// copy 'BatchNumX' to 'current'
+	err = pebbleMakeCheckpoint(checkpointPath, currentPath)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	// open the new 'current'
+	sto, err := pebble.NewPebbleStorage(currentPath, false)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	kvdb.db = sto
+
+	// get currentBatch num
+	kvdb.CurrentBatch, err = kvdb.GetCurrentBatch()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	// idx is obtained from the statedb reset
+	kvdb.CurrentIdx, err = kvdb.GetCurrentIdx()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	return nil
+}
+
+// ResetFromSynchronizer performs a reset in the KVDB getting the state from
+// synchronizerKVDB for the given batchNum.
+func (kvdb *KVDB) ResetFromSynchronizer(batchNum common.BatchNum, synchronizerKVDB *KVDB) error {
+	if synchronizerKVDB == nil {
+		return tracerr.Wrap(fmt.Errorf("synchronizerKVDB can not be nil"))
+	}
+
+	if batchNum == 0 {
+		kvdb.CurrentIdx = 0
+		return nil
+	}
+	synchronizerCheckpointPath := path.Join(synchronizerKVDB.path,
+		fmt.Sprintf("%s%d", PathBatchNum, batchNum))
+	checkpointPath := path.Join(kvdb.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
+	currentPath := path.Join(kvdb.path, PathCurrent)
+
+	// use checkpoint from synchronizerKVDB
+	if _, err := os.Stat(synchronizerCheckpointPath); os.IsNotExist(err) {
+		// if synchronizerKVDB does not have checkpoint at batchNum, return err
+		return tracerr.Wrap(fmt.Errorf("Checkpoint \"%v\" not exist in Synchronizer",
+			synchronizerCheckpointPath))
+	}
+
+	if err := kvdb.db.Pebble().Close(); err != nil {
+		return tracerr.Wrap(err)
+	}
+	// remove 'current'
+	err := os.RemoveAll(currentPath)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	// copy synchronizer'BatchNumX' to 'current'
+	err = pebbleMakeCheckpoint(synchronizerCheckpointPath, currentPath)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	// copy synchronizer'BatchNumX' to 'BatchNumX'
+	err = pebbleMakeCheckpoint(synchronizerCheckpointPath, checkpointPath)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	// open the new 'current'
+	sto, err := pebble.NewPebbleStorage(currentPath, false)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	kvdb.db = sto
+
+	// get currentBatch num
+	kvdb.CurrentBatch, err = kvdb.GetCurrentBatch()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	return nil
+}
+
+// GetCurrentBatch returns the current BatchNum stored in the KVDB
+func (kvdb *KVDB) GetCurrentBatch() (common.BatchNum, error) {
+	cbBytes, err := kvdb.db.Get(KeyCurrentBatch)
+	if tracerr.Unwrap(err) == db.ErrNotFound {
+		return 0, nil
+	}
+	if err != nil {
+		return 0, tracerr.Wrap(err)
+	}
+	return common.BatchNumFromBytes(cbBytes)
+}
+
+// setCurrentBatch stores the current BatchNum in the KVDB
+func (kvdb *KVDB) setCurrentBatch() error {
+	tx, err := kvdb.db.NewTx()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	err = tx.Put(KeyCurrentBatch, kvdb.CurrentBatch.Bytes())
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	if err := tx.Commit(); err != nil {
+		return tracerr.Wrap(err)
+	}
+	return nil
+}
+
+// GetCurrentIdx returns the stored Idx from the KVDB, which is the last Idx
+// used for an Account in the KVDB.
+func (kvdb *KVDB) GetCurrentIdx() (common.Idx, error) {
+	idxBytes, err := kvdb.db.Get(keyCurrentIdx)
+	if tracerr.Unwrap(err) == db.ErrNotFound {
+		return 0, nil
+	}
+	if err != nil {
+		return 0, tracerr.Wrap(err)
+	}
+	return common.IdxFromBytes(idxBytes[:])
+}
+
+// SetCurrentIdx stores Idx in the KVDB
+func (kvdb *KVDB) SetCurrentIdx(idx common.Idx) error {
+	kvdb.CurrentIdx = idx
+
+	tx, err := kvdb.db.NewTx()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	idxBytes, err := idx.Bytes()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	err = tx.Put(keyCurrentIdx, idxBytes[:])
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	if err := tx.Commit(); err != nil {
+		return tracerr.Wrap(err)
+	}
+	return nil
+}
+
+// MakeCheckpoint does a checkpoint at the given batchNum in the defined path.
+// Internally this advances & stores the current BatchNum, and then stores a
+// Checkpoint of the current state of the KVDB.
+func (kvdb *KVDB) MakeCheckpoint() error {
+	// advance currentBatch
+	kvdb.CurrentBatch++
+	log.Debugw("Making KVDB checkpoint", "batch", kvdb.CurrentBatch)
+
+	checkpointPath := path.Join(kvdb.path, fmt.Sprintf("%s%d", PathBatchNum, kvdb.CurrentBatch))
+
+	if err := kvdb.setCurrentBatch(); err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	// if checkpoint BatchNum already exist in disk, delete it
+	if _, err := os.Stat(checkpointPath); !os.IsNotExist(err) {
+		err := os.RemoveAll(checkpointPath)
+		if err != nil {
+			return tracerr.Wrap(err)
+		}
+	} else if err != nil && !os.IsNotExist(err) {
+		return tracerr.Wrap(err)
+	}
+
+	// execute Checkpoint
+	if err := kvdb.db.Pebble().Checkpoint(checkpointPath); err != nil {
+		return tracerr.Wrap(err)
+	}
+	// delete old checkpoints
+	if err := kvdb.deleteOldCheckpoints(); err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	return nil
+}
+
+// DeleteCheckpoint removes if exist the checkpoint of the given batchNum
+func (kvdb *KVDB) DeleteCheckpoint(batchNum common.BatchNum) error {
+	checkpointPath := path.Join(kvdb.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
+
+	if _, err := os.Stat(checkpointPath); os.IsNotExist(err) {
+		return tracerr.Wrap(fmt.Errorf("Checkpoint with batchNum %d does not exist in DB", batchNum))
+	}
+
+	return os.RemoveAll(checkpointPath)
+}
+
+// ListCheckpoints returns the list of batchNums of the checkpoints, sorted.
+// If there's a gap between the list of checkpoints, an error is returned.
+func (kvdb *KVDB) ListCheckpoints() ([]int, error) {
+	files, err := ioutil.ReadDir(kvdb.path)
+	if err != nil {
+		return nil, tracerr.Wrap(err)
+	}
+	checkpoints := []int{}
+	var checkpoint int
+	pattern := fmt.Sprintf("%s%%d", PathBatchNum)
+	for _, file := range files {
+		fileName := file.Name()
+		if file.IsDir() && strings.HasPrefix(fileName, PathBatchNum) {
+			if _, err := fmt.Sscanf(fileName, pattern, &checkpoint); err != nil {
+				return nil, tracerr.Wrap(err)
+			}
+			checkpoints = append(checkpoints, checkpoint)
+		}
+	}
+	sort.Ints(checkpoints)
+	if len(checkpoints) > 0 {
+		first := checkpoints[0]
+		for _, checkpoint := range checkpoints[1:] {
+			first++
+			if checkpoint != first {
+				return nil, tracerr.Wrap(fmt.Errorf("checkpoint gap at %v", checkpoint))
+			}
+		}
+	}
+	return checkpoints, nil
+}
+
+// deleteOldCheckpoints deletes old checkpoints when there are more than
+// `s.keep` checkpoints
+func (kvdb *KVDB) deleteOldCheckpoints() error {
+	list, err := kvdb.ListCheckpoints()
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	if len(list) > kvdb.keep {
+		for _, checkpoint := range list[:len(list)-kvdb.keep] {
+			if err := kvdb.DeleteCheckpoint(common.BatchNum(checkpoint)); err != nil {
+				return tracerr.Wrap(err)
+			}
+		}
+	}
+	return nil
+}
+
+func pebbleMakeCheckpoint(source, dest string) error {
+	// Remove dest folder (if it exists) before doing the checkpoint
+	if _, err := os.Stat(dest); !os.IsNotExist(err) {
+		err := os.RemoveAll(dest)
+		if err != nil {
+			return tracerr.Wrap(err)
+		}
+	} else if err != nil && !os.IsNotExist(err) {
+		return tracerr.Wrap(err)
+	}
+
+	sto, err := pebble.NewPebbleStorage(source, false)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+	defer func() {
+		errClose := sto.Pebble().Close()
+		if errClose != nil {
+			log.Errorw("Pebble.Close", "err", errClose)
+		}
+	}()
+
+	// execute Checkpoint
+	err = sto.Pebble().Checkpoint(dest)
+	if err != nil {
+		return tracerr.Wrap(err)
+	}
+
+	return nil
+}

db/kvdb/kvdb_test.go

@@ -0,0 +1,195 @@
+package kvdb
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func addTestKV(t *testing.T, db *KVDB, k, v []byte) {
+	tx, err := db.db.NewTx()
+	require.NoError(t, err)
+
+	err = tx.Put(k, v)
+	require.NoError(t, err)
+
+	err = tx.Commit()
+	require.NoError(t, err)
+}
+
+func printCheckpoints(t *testing.T, path string) {
+	files, err := ioutil.ReadDir(path)
+	assert.NoError(t, err)
+
+	fmt.Println(path)
+	for _, f := range files {
+		fmt.Println("	" + f.Name())
+	}
+}
+
+func TestCheckpoints(t *testing.T) {
+	dir, err := ioutil.TempDir("", "sdb")
+	require.NoError(t, err)
+	defer assert.NoError(t, os.RemoveAll(dir))
+
+	db, err := NewKVDB(dir, 128)
+	assert.NoError(t, err)
+
+	// add test key-values
+	for i := 0; i < 10; i++ {
+		addTestKV(t, db, []byte{byte(i), byte(i)}, []byte{byte(i * 2), byte(i * 2)})
+	}
+
+	// do checkpoints and check that currentBatch is correct
+	err = db.MakeCheckpoint()
+	assert.NoError(t, err)
+	cb, err := db.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(1), cb)
+
+	for i := 1; i < 10; i++ {
+		err = db.MakeCheckpoint()
+		assert.NoError(t, err)
+
+		cb, err = db.GetCurrentBatch()
+		assert.NoError(t, err)
+		assert.Equal(t, common.BatchNum(i+1), cb)
+	}
+
+	// printCheckpoints(t, sdb.path)
+
+	// reset checkpoint
+	err = db.Reset(3)
+	assert.NoError(t, err)
+
+	// check that reset can be repeated (as there exist the 'current' and
+	// 'BatchNum3', from where the 'current' is a copy)
+	err = db.Reset(3)
+	require.NoError(t, err)
+
+	// check that currentBatch is as expected after Reset
+	cb, err = db.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(3), cb)
+
+	// advance one checkpoint and check that currentBatch is fine
+	err = db.MakeCheckpoint()
+	assert.NoError(t, err)
+	cb, err = db.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(4), cb)
+
+	err = db.DeleteCheckpoint(common.BatchNum(1))
+	assert.NoError(t, err)
+	err = db.DeleteCheckpoint(common.BatchNum(2))
+	assert.NoError(t, err)
+	err = db.DeleteCheckpoint(common.BatchNum(1)) // does not exist, should return err
+	assert.NotNil(t, err)
+	err = db.DeleteCheckpoint(common.BatchNum(2)) // does not exist, should return err
+	assert.NotNil(t, err)
+
+	// Create a new KVDB which will get Reset from the initial KVDB
+	dirLocal, err := ioutil.TempDir("", "ldb")
+	require.NoError(t, err)
+	defer assert.NoError(t, os.RemoveAll(dirLocal))
+	ldb, err := NewKVDB(dirLocal, 128)
+	assert.NoError(t, err)
+
+	// get checkpoint 4 from sdb (StateDB) to ldb (LocalStateDB)
+	err = ldb.ResetFromSynchronizer(4, db)
+	assert.NoError(t, err)
+	// check that currentBatch is 4 after the Reset
+	cb, err = ldb.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(4), cb)
+	// advance one checkpoint in ldb
+	err = ldb.MakeCheckpoint()
+	assert.NoError(t, err)
+	cb, err = ldb.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(5), cb)
+
+	// Create a 3rd KVDB which will get Reset from the initial KVDB
+	dirLocal2, err := ioutil.TempDir("", "ldb2")
+	require.NoError(t, err)
+	defer assert.NoError(t, os.RemoveAll(dirLocal2))
+	ldb2, err := NewKVDB(dirLocal2, 128)
+	assert.NoError(t, err)
+
+	// get checkpoint 4 from sdb (StateDB) to ldb (LocalStateDB)
+	err = ldb2.ResetFromSynchronizer(4, db)
+	assert.NoError(t, err)
+	// check that currentBatch is 4 after the Reset
+	cb, err = ldb2.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(4), cb)
+	// advance one checkpoint in ldb2
+	err = ldb2.MakeCheckpoint()
+	assert.NoError(t, err)
+	cb, err = ldb2.GetCurrentBatch()
+	assert.NoError(t, err)
+	assert.Equal(t, common.BatchNum(5), cb)
+
+	debug := false
+	if debug {
+		printCheckpoints(t, db.path)
+		printCheckpoints(t, ldb.path)
+		printCheckpoints(t, ldb2.path)
+	}
+}
+
+func TestListCheckpoints(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer assert.NoError(t, os.RemoveAll(dir))
+
+	db, err := NewKVDB(dir, 128)
+	require.NoError(t, err)
+
+	numCheckpoints := 16
+	// do checkpoints
+	for i := 0; i < numCheckpoints; i++ {
+		err = db.MakeCheckpoint()
+		require.NoError(t, err)
+	}
+	list, err := db.ListCheckpoints()
+	require.NoError(t, err)
+	assert.Equal(t, numCheckpoints, len(list))
+	assert.Equal(t, 1, list[0])
+	assert.Equal(t, numCheckpoints, list[len(list)-1])
+
+	numReset := 10
+	err = db.Reset(common.BatchNum(numReset))
+	require.NoError(t, err)
+	list, err = db.ListCheckpoints()
+	require.NoError(t, err)
+	assert.Equal(t, numReset, len(list))
+	assert.Equal(t, 1, list[0])
+	assert.Equal(t, numReset, list[len(list)-1])
+}
+
+func TestDeleteOldCheckpoints(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer assert.NoError(t, os.RemoveAll(dir))
+
+	keep := 16
+	db, err := NewKVDB(dir, keep)
+	require.NoError(t, err)
+
+	numCheckpoints := 32
+	// do checkpoints and check that we never have more than `keep`
+	// checkpoints
+	for i := 0; i < numCheckpoints; i++ {
+		err = db.MakeCheckpoint()
+		require.NoError(t, err)
+		checkpoints, err := db.ListCheckpoints()
+		require.NoError(t, err)
+		assert.LessOrEqual(t, len(checkpoints), keep)
+	}
+}

db/statedb/statedb.go

@@ -3,23 +3,16 @@ package statedb
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"math/big"
-	"os"
-	"path"
-	"sort"
-	"strings"
 
 	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/hermeznetwork/hermez-node/db/kvdb"
 	"github.com/hermeznetwork/hermez-node/log"
 	"github.com/hermeznetwork/tracerr"
 	"github.com/iden3/go-merkletree"
 	"github.com/iden3/go-merkletree/db"
-	"github.com/iden3/go-merkletree/db/pebble"
 )
 
-// TODO(Edu): Document here how StateDB is kept consistent
-
 var (
 	// ErrStateDBWithoutMT is used when a method that requires a MerkleTree
 	// is called in a StateDB that does not have a MerkleTree defined
@@ -36,9 +29,6 @@ var (
 	// BJJ with not compatible combination
 	ErrGetIdxNoCase = errors.New("Can not get Idx due unexpected combination of ethereum Address & BabyJubJub PublicKey")
 
-	// KeyCurrentBatch is used as key in the db to store the current BatchNum
-	KeyCurrentBatch = []byte("k:currentbatch")
-
 	// PrefixKeyIdx is the key prefix for idx in the db
 	PrefixKeyIdx = []byte("i:")
 	// PrefixKeyAccHash is the key prefix for account hash in the db
@@ -49,17 +39,9 @@ var (
 	PrefixKeyAddr = []byte("a:")
 	// PrefixKeyAddrBJJ is the key prefix for address-babyjubjub in the db
 	PrefixKeyAddrBJJ = []byte("ab:")
-	// keyidx is used as key in the db to store the current Idx
-	keyidx = []byte("k:idx")
 )
 
 const (
-	// PathBatchNum defines the subpath of the Batch Checkpoint in the
-	// subpath of the StateDB
-	PathBatchNum = "BatchNum"
-	// PathCurrent defines the subpath of the current Batch in the subpath
-	// of the StateDB
-	PathCurrent = "current"
 	// TypeSynchronizer defines a StateDB used by the Synchronizer, that
 	// generates the ExitTree when processing the txs
 	TypeSynchronizer = "synchronizer"
@@ -78,28 +60,26 @@ type TypeStateDB string
 type StateDB struct {
 	path string
 	Typ  TypeStateDB
-	// CurrentIdx holds the current Idx that the BatchBuilder is using
-	CurrentIdx   common.Idx
-	CurrentBatch common.BatchNum
-	db           *pebble.Storage
-	MT           *merkletree.MerkleTree
-	keep         int
+	db   *kvdb.KVDB
+	MT   *merkletree.MerkleTree
+	keep int
 }
 
 // NewStateDB creates a new StateDB, allowing to use an in-memory or in-disk
 // storage.  Checkpoints older than the value defined by `keep` will be
 // deleted.
 func NewStateDB(pathDB string, keep int, typ TypeStateDB, nLevels int) (*StateDB, error) {
-	var sto *pebble.Storage
+	var kv *kvdb.KVDB
 	var err error
-	sto, err = pebble.NewPebbleStorage(path.Join(pathDB, PathCurrent), false)
+
+	kv, err = kvdb.NewKVDB(pathDB, keep)
 	if err != nil {
 		return nil, tracerr.Wrap(err)
 	}
 
 	var mt *merkletree.MerkleTree = nil
 	if typ == TypeSynchronizer || typ == TypeBatchBuilder {
-		mt, err = merkletree.NewMerkleTree(sto.WithPrefix(PrefixKeyMT), nLevels)
+		mt, err = merkletree.NewMerkleTree(kv.StorageWithPrefix(PrefixKeyMT), nLevels)
 		if err != nil {
 			return nil, tracerr.Wrap(err)
 		}
@@ -108,185 +88,47 @@ func NewStateDB(pathDB string, keep int, typ TypeStateDB, nLevels int) (*StateDB
 		return nil, tracerr.Wrap(fmt.Errorf("invalid StateDB parameters: StateDB type==TypeStateDB can not have nLevels!=0"))
 	}
 
-	sdb := &StateDB{
+	return &StateDB{
 		path: pathDB,
-		db:   sto,
+		db:   kv,
 		MT:   mt,
 		Typ:  typ,
 		keep: keep,
-	}
-
-	// load currentBatch
-	sdb.CurrentBatch, err = sdb.GetCurrentBatch()
-	if err != nil {
-		return nil, tracerr.Wrap(err)
-	}
-
-	// make reset (get checkpoint) at currentBatch
-	err = sdb.reset(sdb.CurrentBatch, false)
-	if err != nil {
-		return nil, tracerr.Wrap(err)
-	}
-
-	return sdb, nil
-}
-
-// DB returns the *pebble.Storage from the StateDB
-func (s *StateDB) DB() *pebble.Storage {
-	return s.db
-}
-
-// GetCurrentBatch returns the current BatchNum stored in the StateDB
-func (s *StateDB) GetCurrentBatch() (common.BatchNum, error) {
-	cbBytes, err := s.db.Get(KeyCurrentBatch)
-	if tracerr.Unwrap(err) == db.ErrNotFound {
-		return 0, nil
-	}
-	if err != nil {
-		return 0, tracerr.Wrap(err)
-	}
-	return common.BatchNumFromBytes(cbBytes)
-}
-
-// setCurrentBatch stores the current BatchNum in the StateDB
-func (s *StateDB) setCurrentBatch() error {
-	tx, err := s.db.NewTx()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	err = tx.Put(KeyCurrentBatch, s.CurrentBatch.Bytes())
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	if err := tx.Commit(); err != nil {
-		return tracerr.Wrap(err)
-	}
-	return nil
+	}, nil
 }
 
-// MakeCheckpoint does a checkpoint at the given batchNum in the defined path. Internally this advances & stores the current BatchNum, and then stores a Checkpoint of the current state of the StateDB.
+// MakeCheckpoint does a checkpoint at the given batchNum in the defined path.
+// Internally this advances & stores the current BatchNum, and then stores a
+// Checkpoint of the current state of the StateDB.
 func (s *StateDB) MakeCheckpoint() error {
-	// advance currentBatch
-	s.CurrentBatch++
-	log.Debugw("Making StateDB checkpoint", "batch", s.CurrentBatch, "type", s.Typ)
-
-	checkpointPath := path.Join(s.path, fmt.Sprintf("%s%d", PathBatchNum, s.CurrentBatch))
-
-	if err := s.setCurrentBatch(); err != nil {
-		return tracerr.Wrap(err)
-	}
-
-	// if checkpoint BatchNum already exist in disk, delete it
-	if _, err := os.Stat(checkpointPath); !os.IsNotExist(err) {
-		err := os.RemoveAll(checkpointPath)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-	} else if err != nil && !os.IsNotExist(err) {
-		return tracerr.Wrap(err)
-	}
-
-	// execute Checkpoint
-	if err := s.db.Pebble().Checkpoint(checkpointPath); err != nil {
-		return tracerr.Wrap(err)
-	}
-	// delete old checkpoints
-	if err := s.deleteOldCheckpoints(); err != nil {
-		return tracerr.Wrap(err)
-	}
-
-	return nil
+	log.Debugw("Making StateDB checkpoint", "batch", s.CurrentBatch())
+	return s.db.MakeCheckpoint()
 }
 
-// DeleteCheckpoint removes if exist the checkpoint of the given batchNum
-func (s *StateDB) DeleteCheckpoint(batchNum common.BatchNum) error {
-	checkpointPath := path.Join(s.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
-
-	if _, err := os.Stat(checkpointPath); os.IsNotExist(err) {
-		return tracerr.Wrap(fmt.Errorf("Checkpoint with batchNum %d does not exist in DB", batchNum))
-	}
-
-	return os.RemoveAll(checkpointPath)
+// CurrentBatch returns the current in-memory CurrentBatch of the StateDB.db
+func (s *StateDB) CurrentBatch() common.BatchNum {
+	return s.db.CurrentBatch
 }
 
-// listCheckpoints returns the list of batchNums of the checkpoints, sorted.
-// If there's a gap between the list of checkpoints, an error is returned.
-func (s *StateDB) listCheckpoints() ([]int, error) {
-	files, err := ioutil.ReadDir(s.path)
-	if err != nil {
-		return nil, tracerr.Wrap(err)
-	}
-	checkpoints := []int{}
-	var checkpoint int
-	pattern := fmt.Sprintf("%s%%d", PathBatchNum)
-	for _, file := range files {
-		fileName := file.Name()
-		if file.IsDir() && strings.HasPrefix(fileName, PathBatchNum) {
-			if _, err := fmt.Sscanf(fileName, pattern, &checkpoint); err != nil {
-				return nil, tracerr.Wrap(err)
-			}
-			checkpoints = append(checkpoints, checkpoint)
-		}
-	}
-	sort.Ints(checkpoints)
-	if len(checkpoints) > 0 {
-		first := checkpoints[0]
-		for _, checkpoint := range checkpoints[1:] {
-			first++
-			if checkpoint != first {
-				return nil, tracerr.Wrap(fmt.Errorf("checkpoint gap at %v", checkpoint))
-			}
-		}
-	}
-	return checkpoints, nil
+// CurrentIdx returns the current in-memory CurrentIdx of the StateDB.db
+func (s *StateDB) CurrentIdx() common.Idx {
+	return s.db.CurrentIdx
 }
 
-// deleteOldCheckpoints deletes old checkpoints when there are more than
-// `s.keep` checkpoints
-func (s *StateDB) deleteOldCheckpoints() error {
-	list, err := s.listCheckpoints()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	if len(list) > s.keep {
-		for _, checkpoint := range list[:len(list)-s.keep] {
-			if err := s.DeleteCheckpoint(common.BatchNum(checkpoint)); err != nil {
-				return tracerr.Wrap(err)
-			}
-		}
-	}
-	return nil
+// GetCurrentBatch returns the current BatchNum stored in the StateDB.db
+func (s *StateDB) GetCurrentBatch() (common.BatchNum, error) {
+	return s.db.GetCurrentBatch()
 }
 
-func pebbleMakeCheckpoint(source, dest string) error {
-	// Remove dest folder (if it exists) before doing the checkpoint
-	if _, err := os.Stat(dest); !os.IsNotExist(err) {
-		err := os.RemoveAll(dest)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-	} else if err != nil && !os.IsNotExist(err) {
-		return tracerr.Wrap(err)
-	}
-
-	sto, err := pebble.NewPebbleStorage(source, false)
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	defer func() {
-		errClose := sto.Pebble().Close()
-		if errClose != nil {
-			log.Errorw("Pebble.Close", "err", errClose)
-		}
-	}()
-
-	// execute Checkpoint
-	err = sto.Pebble().Checkpoint(dest)
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
+// GetCurrentIdx returns the stored Idx from the localStateDB, which is the
+// last Idx used for an Account in the localStateDB.
+func (s *StateDB) GetCurrentIdx() (common.Idx, error) {
+	return s.db.GetCurrentIdx()
+}
 
-	return nil
+// SetCurrentIdx stores Idx in the StateDB
+func (s *StateDB) SetCurrentIdx(idx common.Idx) error {
+	return s.db.SetCurrentIdx(idx)
 }
 
 // Reset resets the StateDB to the checkpoint at the given batchNum. Reset
@@ -294,135 +136,30 @@ func pebbleMakeCheckpoint(source, dest string) error {
 // those checkpoints will remain in the storage, and eventually will be
 // deleted when MakeCheckpoint overwrites them.
 func (s *StateDB) Reset(batchNum common.BatchNum) error {
-	return s.reset(batchNum, true)
-}
-
-// reset resets the StateDB to the checkpoint at the given batchNum. Reset
-// does not delete the checkpoints between old current and the new current,
-// those checkpoints will remain in the storage, and eventually will be
-// deleted when MakeCheckpoint overwrites them.  `closeCurrent` will close the
-// currently opened db before doing the reset.
-func (s *StateDB) reset(batchNum common.BatchNum, closeCurrent bool) error {
-	currentPath := path.Join(s.path, PathCurrent)
-
-	if closeCurrent {
-		if err := s.db.Pebble().Close(); err != nil {
-			return tracerr.Wrap(err)
-		}
-	}
-	// remove 'current'
-	err := os.RemoveAll(currentPath)
+	err := s.db.Reset(batchNum)
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
-	// remove all checkpoints > batchNum
-	for i := batchNum + 1; i <= s.CurrentBatch; i++ {
-		if err := s.DeleteCheckpoint(i); err != nil {
-			return tracerr.Wrap(err)
-		}
-	}
-	if batchNum == 0 {
-		// if batchNum == 0, open the new fresh 'current'
-		sto, err := pebble.NewPebbleStorage(currentPath, false)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-		s.db = sto
-		s.CurrentIdx = 255
-		s.CurrentBatch = batchNum
-
-		if s.MT != nil {
-			// open the MT for the current s.db
-			mt, err := merkletree.NewMerkleTree(s.db.WithPrefix(PrefixKeyMT), s.MT.MaxLevels())
-			if err != nil {
-				return tracerr.Wrap(err)
-			}
-			s.MT = mt
-		}
-		return nil
-	}
-
-	checkpointPath := path.Join(s.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
-	// copy 'BatchNumX' to 'current'
-	err = pebbleMakeCheckpoint(checkpointPath, currentPath)
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-
-	// open the new 'current'
-	sto, err := pebble.NewPebbleStorage(currentPath, false)
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	s.db = sto
-
-	// get currentBatch num
-	s.CurrentBatch, err = s.GetCurrentBatch()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	// idx is obtained from the statedb reset
-	s.CurrentIdx, err = s.GetIdx()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-
 	if s.MT != nil {
 		// open the MT for the current s.db
-		mt, err := merkletree.NewMerkleTree(s.db.WithPrefix(PrefixKeyMT), s.MT.MaxLevels())
+		mt, err := merkletree.NewMerkleTree(s.db.StorageWithPrefix(PrefixKeyMT), s.MT.MaxLevels())
 		if err != nil {
 			return tracerr.Wrap(err)
 		}
 		s.MT = mt
 	}
-
-	return nil
-}
-
-// GetIdx returns the stored Idx from the localStateDB, which is the last Idx
-// used for an Account in the localStateDB.
-func (s *StateDB) GetIdx() (common.Idx, error) {
-	idxBytes, err := s.DB().Get(keyidx)
-	if tracerr.Unwrap(err) == db.ErrNotFound {
-		return 0, nil
-	}
-	if err != nil {
-		return 0, tracerr.Wrap(err)
-	}
-	return common.IdxFromBytes(idxBytes[:])
-}
-
-// SetIdx stores Idx in the localStateDB
-func (s *StateDB) SetIdx(idx common.Idx) error {
-	s.CurrentIdx = idx
-
-	tx, err := s.DB().NewTx()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	idxBytes, err := idx.Bytes()
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	err = tx.Put(keyidx, idxBytes[:])
-	if err != nil {
-		return tracerr.Wrap(err)
-	}
-	if err := tx.Commit(); err != nil {
-		return tracerr.Wrap(err)
-	}
 	return nil
 }
 
 // GetAccount returns the account for the given Idx
 func (s *StateDB) GetAccount(idx common.Idx) (*common.Account, error) {
-	return GetAccountInTreeDB(s.db, idx)
+	return GetAccountInTreeDB(s.db.DB(), idx)
 }
 
 // GetAccounts returns all the accounts in the db.  Use for debugging pruposes
 // only.
 func (s *StateDB) GetAccounts() ([]common.Account, error) {
-	idxDB := s.db.WithPrefix(PrefixKeyIdx)
+	idxDB := s.db.StorageWithPrefix(PrefixKeyIdx)
 	idxs := []common.Idx{}
 	// NOTE: Current implementation of Iterate in the pebble interface is
 	// not efficient, as it iterates over all keys.  Improve it following
@@ -477,7 +214,7 @@ func GetAccountInTreeDB(sto db.Storage, idx common.Idx) (*common.Account, error)
 // StateDB.MT==nil, MerkleTree is not affected, otherwise updates the
 // MerkleTree, returning a CircomProcessorProof.
 func (s *StateDB) CreateAccount(idx common.Idx, account *common.Account) (*merkletree.CircomProcessorProof, error) {
-	cpp, err := CreateAccountInTreeDB(s.db, s.MT, idx, account)
+	cpp, err := CreateAccountInTreeDB(s.db.DB(), s.MT, idx, account)
 	if err != nil {
 		return cpp, tracerr.Wrap(err)
 	}
@@ -540,7 +277,7 @@ func CreateAccountInTreeDB(sto db.Storage, mt *merkletree.MerkleTree, idx common
 // StateDB.mt==nil, MerkleTree is not affected, otherwise updates the
 // MerkleTree, returning a CircomProcessorProof.
 func (s *StateDB) UpdateAccount(idx common.Idx, account *common.Account) (*merkletree.CircomProcessorProof, error) {
-	return UpdateAccountInTreeDB(s.db, s.MT, idx, account)
+	return UpdateAccountInTreeDB(s.db.DB(), s.MT, idx, account)
 }
 
 // UpdateAccountInTreeDB is abstracted from StateDB to be used from StateDB and
@@ -623,68 +360,24 @@ func NewLocalStateDB(path string, keep int, synchronizerDB *StateDB, typ TypeSta
 }
 
 // Reset performs a reset in the LocaStateDB. If fromSynchronizer is true, it
-// gets the state from LocalStateDB.synchronizerStateDB for the given batchNum. If fromSynchronizer is false, get the state from LocalStateDB checkpoints.
+// gets the state from LocalStateDB.synchronizerStateDB for the given batchNum.
+// If fromSynchronizer is false, get the state from LocalStateDB checkpoints.
 func (l *LocalStateDB) Reset(batchNum common.BatchNum, fromSynchronizer bool) error {
-	if batchNum == 0 {
-		l.CurrentIdx = 0
-		return nil
-	}
-
-	synchronizerCheckpointPath := path.Join(l.synchronizerStateDB.path,
-		fmt.Sprintf("%s%d", PathBatchNum, batchNum))
-	checkpointPath := path.Join(l.path, fmt.Sprintf("%s%d", PathBatchNum, batchNum))
-	currentPath := path.Join(l.path, PathCurrent)
-
 	if fromSynchronizer {
-		// use checkpoint from SynchronizerStateDB
-		if _, err := os.Stat(synchronizerCheckpointPath); os.IsNotExist(err) {
-			// if synchronizerStateDB does not have checkpoint at batchNum, return err
-			return tracerr.Wrap(fmt.Errorf("Checkpoint \"%v\" not exist in Synchronizer",
-				synchronizerCheckpointPath))
-		}
-
-		if err := l.db.Pebble().Close(); err != nil {
-			return tracerr.Wrap(err)
-		}
-		// remove 'current'
-		err := os.RemoveAll(currentPath)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-		// copy synchronizer'BatchNumX' to 'current'
-		err = pebbleMakeCheckpoint(synchronizerCheckpointPath, currentPath)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-		// copy synchronizer'BatchNumX' to 'BatchNumX'
-		err = pebbleMakeCheckpoint(synchronizerCheckpointPath, checkpointPath)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-
-		// open the new 'current'
-		sto, err := pebble.NewPebbleStorage(currentPath, false)
-		if err != nil {
-			return tracerr.Wrap(err)
-		}
-		l.db = sto
-
-		// get currentBatch num
-		l.CurrentBatch, err = l.GetCurrentBatch()
+		err := l.db.ResetFromSynchronizer(batchNum, l.synchronizerStateDB.db)
 		if err != nil {
 			return tracerr.Wrap(err)
 		}
 		// open the MT for the current s.db
 		if l.MT != nil {
-			mt, err := merkletree.NewMerkleTree(l.db.WithPrefix(PrefixKeyMT), l.MT.MaxLevels())
+			mt, err := merkletree.NewMerkleTree(l.db.StorageWithPrefix(PrefixKeyMT), l.MT.MaxLevels())
 			if err != nil {
 				return tracerr.Wrap(err)
 			}
 			l.MT = mt
 		}
-
 		return nil
 	}
 	// use checkpoint from LocalStateDB
-	return l.StateDB.reset(batchNum, true)
+	return l.StateDB.Reset(batchNum)
 }

db/statedb/statedb_test.go

@@ -55,13 +55,13 @@ func TestNewStateDBIntermediateState(t *testing.T) {
 	v1 := []byte("testvalue1")
 
 	// store some data
-	tx, err := sdb.db.NewTx()
+	tx, err := sdb.db.DB().NewTx()
 	assert.NoError(t, err)
 	err = tx.Put(k0, v0)
 	assert.NoError(t, err)
 	err = tx.Commit()
 	assert.NoError(t, err)
-	v, err := sdb.db.Get(k0)
+	v, err := sdb.db.DB().Get(k0)
 	assert.NoError(t, err)
 	assert.Equal(t, v0, v)
 
@@ -69,41 +69,41 @@ func TestNewStateDBIntermediateState(t *testing.T) {
 	// executing a Reset (discarding the last 'testkey0'&'testvalue0' data)
 	sdb, err = NewStateDB(dir, 128, TypeTxSelector, 0)
 	assert.NoError(t, err)
-	v, err = sdb.db.Get(k0)
+	v, err = sdb.db.DB().Get(k0)
 	assert.NotNil(t, err)
 	assert.Equal(t, db.ErrNotFound, tracerr.Unwrap(err))
 	assert.Nil(t, v)
 
 	// store the same data from the beginning that has ben lost since last NewStateDB
-	tx, err = sdb.db.NewTx()
+	tx, err = sdb.db.DB().NewTx()
 	assert.NoError(t, err)
 	err = tx.Put(k0, v0)
 	assert.NoError(t, err)
 	err = tx.Commit()
 	assert.NoError(t, err)
-	v, err = sdb.db.Get(k0)
+	v, err = sdb.db.DB().Get(k0)
 	assert.NoError(t, err)
 	assert.Equal(t, v0, v)
 
 	// make checkpoints with the current state
-	bn, err := sdb.GetCurrentBatch()
+	bn, err := sdb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(0), bn)
-	err = sdb.MakeCheckpoint()
+	err = sdb.db.MakeCheckpoint()
 	assert.NoError(t, err)
-	bn, err = sdb.GetCurrentBatch()
+	bn, err = sdb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(1), bn)
 
 	// write more data
-	tx, err = sdb.db.NewTx()
+	tx, err = sdb.db.DB().NewTx()
 	assert.NoError(t, err)
 	err = tx.Put(k1, v1)
 	assert.NoError(t, err)
 	err = tx.Commit()
 	assert.NoError(t, err)
 
-	v, err = sdb.db.Get(k1)
+	v, err = sdb.db.DB().Get(k1)
 	assert.NoError(t, err)
 	assert.Equal(t, v1, v)
 
@@ -112,11 +112,11 @@ func TestNewStateDBIntermediateState(t *testing.T) {
 	sdb, err = NewStateDB(dir, 128, TypeTxSelector, 0)
 	assert.NoError(t, err)
 
-	v, err = sdb.db.Get(k0)
+	v, err = sdb.db.DB().Get(k0)
 	assert.NoError(t, err)
 	assert.Equal(t, v0, v)
 
-	v, err = sdb.db.Get(k1)
+	v, err = sdb.db.DB().Get(k1)
 	assert.NotNil(t, err)
 	assert.Equal(t, db.ErrNotFound, tracerr.Unwrap(err))
 	assert.Nil(t, v)
@@ -228,6 +228,8 @@ func TestStateDBWithMT(t *testing.T) {
 	assert.Equal(t, accounts[0].Nonce, a.Nonce)
 }
 
+// TestCheckpoints performs almost the same test than kvdb/kvdb_test.go
+// TestCheckpoints, but over the StateDB
 func TestCheckpoints(t *testing.T) {
 	dir, err := ioutil.TempDir("", "sdb")
 	require.NoError(t, err)
@@ -249,17 +251,17 @@ func TestCheckpoints(t *testing.T) {
 	}
 
 	// do checkpoints and check that currentBatch is correct
-	err = sdb.MakeCheckpoint()
+	err = sdb.db.MakeCheckpoint()
 	assert.NoError(t, err)
-	cb, err := sdb.GetCurrentBatch()
+	cb, err := sdb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(1), cb)
 
 	for i := 1; i < 10; i++ {
-		err = sdb.MakeCheckpoint()
+		err = sdb.db.MakeCheckpoint()
 		assert.NoError(t, err)
 
-		cb, err = sdb.GetCurrentBatch()
+		cb, err = sdb.db.GetCurrentBatch()
 		assert.NoError(t, err)
 		assert.Equal(t, common.BatchNum(i+1), cb)
 	}
@@ -276,24 +278,24 @@ func TestCheckpoints(t *testing.T) {
 	require.NoError(t, err)
 
 	// check that currentBatch is as expected after Reset
-	cb, err = sdb.GetCurrentBatch()
+	cb, err = sdb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(3), cb)
 
 	// advance one checkpoint and check that currentBatch is fine
-	err = sdb.MakeCheckpoint()
+	err = sdb.db.MakeCheckpoint()
 	assert.NoError(t, err)
-	cb, err = sdb.GetCurrentBatch()
+	cb, err = sdb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(4), cb)
 
-	err = sdb.DeleteCheckpoint(common.BatchNum(1))
+	err = sdb.db.DeleteCheckpoint(common.BatchNum(1))
 	assert.NoError(t, err)
-	err = sdb.DeleteCheckpoint(common.BatchNum(2))
+	err = sdb.db.DeleteCheckpoint(common.BatchNum(2))
 	assert.NoError(t, err)
-	err = sdb.DeleteCheckpoint(common.BatchNum(1)) // does not exist, should return err
+	err = sdb.db.DeleteCheckpoint(common.BatchNum(1)) // does not exist, should return err
 	assert.NotNil(t, err)
-	err = sdb.DeleteCheckpoint(common.BatchNum(2)) // does not exist, should return err
+	err = sdb.db.DeleteCheckpoint(common.BatchNum(2)) // does not exist, should return err
 	assert.NotNil(t, err)
 
 	// Create a LocalStateDB from the initial StateDB
@@ -307,13 +309,13 @@ func TestCheckpoints(t *testing.T) {
 	err = ldb.Reset(4, true)
 	assert.NoError(t, err)
 	// check that currentBatch is 4 after the Reset
-	cb, err = ldb.GetCurrentBatch()
+	cb, err = ldb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(4), cb)
 	// advance one checkpoint in ldb
-	err = ldb.MakeCheckpoint()
+	err = ldb.db.MakeCheckpoint()
 	assert.NoError(t, err)
-	cb, err = ldb.GetCurrentBatch()
+	cb, err = ldb.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(5), cb)
 
@@ -328,13 +330,13 @@ func TestCheckpoints(t *testing.T) {
 	err = ldb2.Reset(4, true)
 	assert.NoError(t, err)
 	// check that currentBatch is 4 after the Reset
-	cb, err = ldb2.GetCurrentBatch()
+	cb, err = ldb2.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(4), cb)
 	// advance one checkpoint in ldb2
-	err = ldb2.MakeCheckpoint()
+	err = ldb2.db.MakeCheckpoint()
 	assert.NoError(t, err)
-	cb, err = ldb2.GetCurrentBatch()
+	cb, err = ldb2.db.GetCurrentBatch()
 	assert.NoError(t, err)
 	assert.Equal(t, common.BatchNum(5), cb)
 
@@ -464,6 +466,8 @@ func TestCheckAccountsTreeTestVectors(t *testing.T) {
 	assert.Equal(t, "17298264051379321456969039521810887093935433569451713402227686942080129181291", sdb.MT.Root().BigInt().String())
 }
 
+// TestListCheckpoints performs almost the same test than kvdb/kvdb_test.go
+// TestListCheckpoints, but over the StateDB
 func TestListCheckpoints(t *testing.T) {
 	dir, err := ioutil.TempDir("", "tmpdb")
 	require.NoError(t, err)
@@ -475,10 +479,10 @@ func TestListCheckpoints(t *testing.T) {
 	numCheckpoints := 16
 	// do checkpoints
 	for i := 0; i < numCheckpoints; i++ {
-		err = sdb.MakeCheckpoint()
+		err = sdb.db.MakeCheckpoint()
 		require.NoError(t, err)
 	}
-	list, err := sdb.listCheckpoints()
+	list, err := sdb.db.ListCheckpoints()
 	require.NoError(t, err)
 	assert.Equal(t, numCheckpoints, len(list))
 	assert.Equal(t, 1, list[0])
@@ -487,13 +491,15 @@ func TestListCheckpoints(t *testing.T) {
 	numReset := 10
 	err = sdb.Reset(common.BatchNum(numReset))
 	require.NoError(t, err)
-	list, err = sdb.listCheckpoints()
+	list, err = sdb.db.ListCheckpoints()
 	require.NoError(t, err)
 	assert.Equal(t, numReset, len(list))
 	assert.Equal(t, 1, list[0])
 	assert.Equal(t, numReset, list[len(list)-1])
 }
 
+// TestDeleteOldCheckpoints performs almost the same test than
+// kvdb/kvdb_test.go TestDeleteOldCheckpoints, but over the StateDB
 func TestDeleteOldCheckpoints(t *testing.T) {
 	dir, err := ioutil.TempDir("", "tmpdb")
 	require.NoError(t, err)
@@ -507,9 +513,9 @@ func TestDeleteOldCheckpoints(t *testing.T) {
 	// do checkpoints and check that we never have more than `keep`
 	// checkpoints
 	for i := 0; i < numCheckpoints; i++ {
-		err = sdb.MakeCheckpoint()
+		err = sdb.db.MakeCheckpoint()
 		require.NoError(t, err)
-		checkpoints, err := sdb.listCheckpoints()
+		checkpoints, err := sdb.db.ListCheckpoints()
 		require.NoError(t, err)
 		assert.LessOrEqual(t, len(checkpoints), keep)
 	}

db/statedb/utils.go

@@ -48,7 +48,7 @@ func (s *StateDB) setIdxByEthAddrBJJ(idx common.Idx, addr ethCommon.Address, pk
 	// have an Idx stored in the DB, and if so, the already stored Idx is
 	// bigger than the given one, so should be updated to the new one
 	// (smaller)
-	tx, err := s.db.NewTx()
+	tx, err := s.db.DB().NewTx()
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
@@ -81,7 +81,7 @@ func (s *StateDB) setIdxByEthAddrBJJ(idx common.Idx, addr ethCommon.Address, pk
 // not found in the StateDB.
 func (s *StateDB) GetIdxByEthAddr(addr ethCommon.Address, tokenID common.TokenID) (common.Idx, error) {
 	k := concatEthAddrTokenID(addr, tokenID)
-	b, err := s.db.Get(append(PrefixKeyAddr, k...))
+	b, err := s.db.DB().Get(append(PrefixKeyAddr, k...))
 	if err != nil {
 		return common.Idx(0), tracerr.Wrap(fmt.Errorf("GetIdxByEthAddr: %s: ToEthAddr: %s, TokenID: %d",
 			ErrToIdxNotFound, addr.Hex(), tokenID))
@@ -107,7 +107,7 @@ func (s *StateDB) GetIdxByEthAddrBJJ(addr ethCommon.Address, pk babyjub.PublicKe
 	} else if !bytes.Equal(addr.Bytes(), common.EmptyAddr.Bytes()) && pk != common.EmptyBJJComp {
 		// case ToEthAddr!=0 && ToBJJ!=0
 		k := concatEthAddrBJJTokenID(addr, pk, tokenID)
-		b, err := s.db.Get(append(PrefixKeyAddrBJJ, k...))
+		b, err := s.db.DB().Get(append(PrefixKeyAddrBJJ, k...))
 		if err != nil {
 			return common.Idx(0), tracerr.Wrap(fmt.Errorf("GetIdxByEthAddrBJJ: %s: ToEthAddr: %s, ToBJJ: %s, TokenID: %d", ErrToIdxNotFound, addr.Hex(), pk, tokenID))
 		}

txprocessor/txprocessor.go

@@ -114,10 +114,10 @@ func (tp *TxProcessor) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinat
 
 	if tp.s.Typ == statedb.TypeBatchBuilder {
 		tp.zki = common.NewZKInputs(tp.config.ChainID, tp.config.MaxTx, tp.config.MaxL1Tx,
-			tp.config.MaxFeeTx, tp.config.NLevels, tp.s.CurrentBatch.BigInt())
-		tp.zki.OldLastIdx = tp.s.CurrentIdx.BigInt()
+			tp.config.MaxFeeTx, tp.config.NLevels, tp.s.CurrentBatch().BigInt())
+		tp.zki.OldLastIdx = tp.s.CurrentIdx().BigInt()
 		tp.zki.OldStateRoot = tp.s.MT.Root().BigInt()
-		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx
+		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx()
 	}
 
 	// TBD if ExitTree is only in memory or stored in disk, for the moment
@@ -169,7 +169,7 @@ func (tp *TxProcessor) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinat
 			tp.zki.Metadata.L1TxsDataAvailability =
 				append(tp.zki.Metadata.L1TxsDataAvailability, l1TxDataAvailability)
 
-			tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx.BigInt()
+			tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx().BigInt()
 			tp.zki.ISStateRoot[tp.i] = tp.s.MT.Root().BigInt()
 			if exitIdx == nil {
 				tp.zki.ISExitRoot[tp.i] = exitTree.Root().BigInt()
@@ -214,7 +214,7 @@ func (tp *TxProcessor) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinat
 			tp.zki.Metadata.L1TxsDataAvailability =
 				append(tp.zki.Metadata.L1TxsDataAvailability, l1TxDataAvailability)
 
-			tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx.BigInt()
+			tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx().BigInt()
 			tp.zki.ISStateRoot[tp.i] = tp.s.MT.Root().BigInt()
 			tp.i++
 		}
@@ -268,7 +268,7 @@ func (tp *TxProcessor) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinat
 
 			// Intermediate States
 			if tp.i < nTx-1 {
-				tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx.BigInt()
+				tp.zki.ISOutIdx[tp.i] = tp.s.CurrentIdx().BigInt()
 				tp.zki.ISStateRoot[tp.i] = tp.s.MT.Root().BigInt()
 				tp.zki.ISAccFeeOut[tp.i] = formatAccumulatedFees(collectedFees, tp.zki.FeePlanTokens)
 				if exitIdx == nil {
@@ -296,7 +296,7 @@ func (tp *TxProcessor) ProcessTxs(coordIdxs []common.Idx, l1usertxs, l1coordinat
 		}
 		for i := last; i < int(tp.config.MaxTx); i++ {
 			if i < int(tp.config.MaxTx)-1 {
-				tp.zki.ISOutIdx[i] = tp.s.CurrentIdx.BigInt()
+				tp.zki.ISOutIdx[i] = tp.s.CurrentIdx().BigInt()
 				tp.zki.ISStateRoot[i] = tp.s.MT.Root().BigInt()
 				tp.zki.ISAccFeeOut[i] = formatAccumulatedFees(collectedFees, tp.zki.FeePlanTokens)
 				tp.zki.ISExitRoot[i] = exitTree.Root().BigInt()
@@ -541,7 +541,7 @@ func (tp *TxProcessor) ProcessL1Tx(exitTree *merkletree.MerkleTree, tx *common.L
 		(tx.Type == common.TxTypeCreateAccountDeposit ||
 			tx.Type == common.TxTypeCreateAccountDepositTransfer) {
 		var err error
-		createdAccount, err = tp.s.GetAccount(tp.s.CurrentIdx)
+		createdAccount, err = tp.s.GetAccount(tp.s.CurrentIdx())
 		if err != nil {
 			log.Error(err)
 			return nil, nil, false, nil, tracerr.Wrap(err)
@@ -664,7 +664,7 @@ func (tp *TxProcessor) applyCreateAccount(tx *common.L1Tx) error {
 		EthAddr:   tx.FromEthAddr,
 	}
 
-	p, err := tp.s.CreateAccount(common.Idx(tp.s.CurrentIdx+1), account)
+	p, err := tp.s.CreateAccount(common.Idx(tp.s.CurrentIdx()+1), account)
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
@@ -685,9 +685,9 @@ func (tp *TxProcessor) applyCreateAccount(tx *common.L1Tx) error {
 		tp.zki.OldKey1[tp.i] = p.OldKey.BigInt()
 		tp.zki.OldValue1[tp.i] = p.OldValue.BigInt()
 
-		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx + 1
+		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx() + 1
 
-		tp.zki.AuxFromIdx[tp.i] = common.Idx(tp.s.CurrentIdx + 1).BigInt()
+		tp.zki.AuxFromIdx[tp.i] = common.Idx(tp.s.CurrentIdx() + 1).BigInt()
 		tp.zki.NewAccount[tp.i] = big.NewInt(1)
 
 		if tp.i < len(tp.zki.ISOnChain) { // len(tp.zki.ISOnChain) == nTx
@@ -696,7 +696,7 @@ func (tp *TxProcessor) applyCreateAccount(tx *common.L1Tx) error {
 		}
 	}
 
-	return tp.s.SetIdx(tp.s.CurrentIdx + 1)
+	return tp.s.SetCurrentIdx(tp.s.CurrentIdx() + 1)
 }
 
 // applyDeposit updates the balance in the account of the depositer, if
@@ -894,7 +894,7 @@ func (tp *TxProcessor) applyTransfer(coordIdxsMap map[common.TokenID]common.Idx,
 // applyCreateAccountDepositTransfer, in a single tx, creates a new account,
 // makes a deposit, and performs a transfer to another account
 func (tp *TxProcessor) applyCreateAccountDepositTransfer(tx *common.L1Tx) error {
-	auxFromIdx := common.Idx(tp.s.CurrentIdx + 1)
+	auxFromIdx := common.Idx(tp.s.CurrentIdx() + 1)
 	accSender := &common.Account{
 		TokenID:   tx.TokenID,
 		Nonce:     0,
@@ -920,7 +920,7 @@ func (tp *TxProcessor) applyCreateAccountDepositTransfer(tx *common.L1Tx) error
 	accSender.Balance = new(big.Int).Sub(accSender.Balance, tx.EffectiveAmount)
 
 	// create Account of the Sender
-	p, err := tp.s.CreateAccount(common.Idx(tp.s.CurrentIdx+1), accSender)
+	p, err := tp.s.CreateAccount(common.Idx(tp.s.CurrentIdx()+1), accSender)
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
@@ -932,7 +932,7 @@ func (tp *TxProcessor) applyCreateAccountDepositTransfer(tx *common.L1Tx) error
 		tp.zki.OldKey1[tp.i] = p.OldKey.BigInt()
 		tp.zki.OldValue1[tp.i] = p.OldValue.BigInt()
 
-		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx + 1
+		tp.zki.Metadata.NewLastIdxRaw = tp.s.CurrentIdx() + 1
 
 		tp.zki.AuxFromIdx[tp.i] = auxFromIdx.BigInt()
 		tp.zki.NewAccount[tp.i] = big.NewInt(1)
@@ -976,7 +976,7 @@ func (tp *TxProcessor) applyCreateAccountDepositTransfer(tx *common.L1Tx) error
 		tp.zki.Siblings2[tp.i] = siblingsToZKInputFormat(p.Siblings)
 	}
 
-	return tp.s.SetIdx(tp.s.CurrentIdx + 1)
+	return tp.s.SetCurrentIdx(tp.s.CurrentIdx() + 1)
 }
 
 // It returns the ExitAccount and a boolean determining if the Exit created a