diff --git a/cmd/chai/commands/pebble.go b/cmd/chai/commands/pebble.go
index fbcb5c31..c0f14779 100644
--- a/cmd/chai/commands/pebble.go
+++ b/cmd/chai/commands/pebble.go
@@ -2,6 +2,7 @@ package commands
 
 import (
 	"github.com/chaisql/chai/cmd/chai/dbutil"
+	"github.com/chaisql/chai/internal/kv"
 	"github.com/urfave/cli/v2"
 )
 
@@ -35,7 +36,8 @@ func NewPebbleCommand() *cli.Command {
 		}
 		defer db.Close()
 
-		return dbutil.DumpPebble(c.Context, db.DB.Store.DB(), dbutil.DumpPebbleOptions{
+		ng := db.DB.Engine.(*kv.PebbleEngine)
+		return dbutil.DumpPebble(c.Context, ng.DB(), dbutil.DumpPebbleOptions{
 			KeysOnly: c.Bool("keys-only"),
 		})
 	}
diff --git a/internal/database/database.go b/internal/database/database.go
index f4877e5d..a8c12833 100644
--- a/internal/database/database.go
+++ b/internal/database/database.go
@@ -6,6 +6,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/chaisql/chai/internal/kv"
 	"github.com/cockroachdb/errors"
 )
@@ -41,7 +42,7 @@ type Database struct {
 	closeOnce sync.Once
 
 	// Underlying kv store.
-	Store *kv.Store
+	Engine engine.Engine
 }
 
 // Options are passed to Open to control
@@ -54,7 +55,7 @@ type Options struct {
 // It may parse a SQL representation of the catalog
 // and return a Catalog that represents all entities stored on disk.
 type CatalogLoader interface {
-	LoadCatalog(kv.Session) (*Catalog, error)
+	LoadCatalog(engine.Session) (*Catalog, error)
 }
 
 // TxOptions are passed to Begin to configure transactions.
@@ -78,18 +79,18 @@ func Open(path string, opts *Options) (*Database, error) {
 	}
 
 	db := Database{
-		Store: store,
+		Engine: store,
 	}
 
 	// ensure the rollback segment doesn't contain any data that needs to be rolled back
 	// due to a previous crash.
-	err = db.Store.ResetRollbackSegment()
+	err = db.Engine.Recover()
 	if err != nil {
 		return nil, err
 	}
 
 	// clean up the transient namespaces
-	err = db.Store.CleanupTransientNamespaces()
+	err = db.Engine.CleanupTransientNamespaces()
 	if err != nil {
 		return nil, err
 	}
@@ -167,7 +168,7 @@ func (db *Database) closeDatabase() error {
 		return err
 	}
 
-	return db.Store.Close()
+	return db.Engine.Close()
 }
 
 // GetAttachedTx returns the transaction attached to the database. It returns nil if there is no
@@ -222,16 +223,16 @@ func (db *Database) beginTx(opts *TxOptions) (*Transaction, error) {
 		opts = &TxOptions{}
 	}
 
-	var sess kv.Session
+	var sess engine.Session
 	if opts.ReadOnly {
-		sess = db.Store.NewSnapshotSession()
+		sess = db.Engine.NewSnapshotSession()
 	} else {
-		sess = db.Store.NewBatchSession()
+		sess = db.Engine.NewBatchSession()
 	}
 
 	tx := Transaction{
 		db:       db,
-		Store:    db.Store,
+		Engine:   db.Engine,
 		Session:  sess,
 		Writable: !opts.ReadOnly,
 		ID:       atomic.AddUint64(&db.TransactionIDs, 1),
diff --git a/internal/database/index.go b/internal/database/index.go
index 923347c8..5eb81a43 100644
--- a/internal/database/index.go
+++ b/internal/database/index.go
@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"fmt"
 
-	"github.com/chaisql/chai/internal/kv"
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/chaisql/chai/internal/tree"
 	"github.com/chaisql/chai/internal/types"
 	"github.com/cockroachdb/errors"
@@ -122,7 +122,7 @@ func (idx *Index) Delete(vs []types.Value, key []byte) error {
 		return err
 	}
 
-	return errors.WithStack(kv.ErrKeyNotFound)
+	return errors.WithStack(engine.ErrKeyNotFound)
 }
 
 func (idx *Index) IterateOnRange(rng *tree.Range, reverse bool, fn func(key *tree.Key) error) error {
diff --git a/internal/database/table.go b/internal/database/table.go
index 2ca44aa4..9477b13a 100644
--- a/internal/database/table.go
+++ b/internal/database/table.go
@@ -3,8 +3,8 @@ package database
 import (
 	"fmt"
 
+	"github.com/chaisql/chai/internal/engine"
 	errs "github.com/chaisql/chai/internal/errors"
-	"github.com/chaisql/chai/internal/kv"
 	"github.com/chaisql/chai/internal/object"
 	"github.com/chaisql/chai/internal/tree"
 	"github.com/chaisql/chai/internal/types"
@@ -55,7 +55,7 @@ func (t *Table) Insert(o types.Object) (*tree.Key, Row, error) {
 		err = t.Tree.Put(key, enc)
 	}
 	if err != nil {
-		if errors.Is(err, kv.ErrKeyAlreadyExists) {
+		if errors.Is(err, engine.ErrKeyAlreadyExists) {
 			return nil, nil, &ConstraintViolationError{
 				Constraint: "PRIMARY KEY",
 				Paths:      t.Info.PrimaryKey.Paths,
@@ -95,7 +95,7 @@ func (t *Table) Delete(key *tree.Key) error {
 	}
 
 	err := t.Tree.Delete(key)
-	if errors.Is(err, kv.ErrKeyNotFound) {
+	if errors.Is(err, engine.ErrKeyNotFound) {
 		return errors.WithStack(errs.NewNotFoundError(key.String()))
 	}
 
@@ -178,7 +178,7 @@ func (t *Table) IterateOnRange(rng *Range, reverse bool, fn func(key *tree.Key,
 func (t *Table) GetRow(key *tree.Key) (Row, error) {
 	enc, err := t.Tree.Get(key)
 	if err != nil {
-		if errors.Is(err, kv.ErrKeyNotFound) {
+		if errors.Is(err, engine.ErrKeyNotFound) {
 			return nil, errors.WithStack(errs.NewNotFoundError(key.String()))
 		}
 		return nil, fmt.Errorf("failed to fetch row %q: %w", key, err)
diff --git a/internal/database/transaction.go b/internal/database/transaction.go
index 5c681446..82f73873 100644
--- a/internal/database/transaction.go
+++ b/internal/database/transaction.go
@@ -4,7 +4,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/chaisql/chai/internal/kv"
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/cockroachdb/errors"
 )
 
@@ -19,8 +19,8 @@ type Transaction struct {
 	// The timestamp must use the local timezone.
 	TxStart time.Time
 
-	Session   kv.Session
-	Store     *kv.Store
+	Session   engine.Session
+	Engine    engine.Engine
 	ID        uint64
 	Writable  bool
 	WriteTxMu *sync.Mutex
@@ -41,7 +41,7 @@ func (tx *Transaction) Rollback() error {
 	}
 
 	if tx.Writable {
-		err = tx.Store.Rollback()
+		err = tx.Engine.Rollback()
 		if err != nil {
 			return err
 		}
diff --git a/internal/engine/engine.go b/internal/engine/engine.go
new file mode 100644
index 00000000..86ee9856
--- /dev/null
+++ b/internal/engine/engine.go
@@ -0,0 +1,66 @@
+package engine
+
+import "github.com/cockroachdb/errors"
+
+// Common errors returned by the engine.
+var (
+	// ErrKeyNotFound is returned when the targeted key doesn't exist.
+	ErrKeyNotFound = errors.New("key not found")
+
+	// ErrKeyAlreadyExists is returned when the targeted key already exists.
+	ErrKeyAlreadyExists = errors.New("key already exists")
+)
+
+type Engine interface {
+	Close() error
+	Rollback() error
+	Recover() error
+	LockSharedSnapshot()
+	UnlockSharedSnapshot()
+	CleanupTransientNamespaces() error
+	NewSnapshotSession() Session
+	NewBatchSession() Session
+	NewTransientSession() Session
+}
+
+type Session interface {
+	Commit() error
+	Close() error
+	// Insert inserts a key-value pair. If it already exists, it returns ErrKeyAlreadyExists.
+	Insert(k, v []byte) error
+	// Put stores a key-value pair. If it already exists, it overrides it.
+	Put(k, v []byte) error
+	// Get returns a value associated with the given key. If not found, returns ErrKeyNotFound.
+	Get(k []byte) ([]byte, error)
+	// Exists returns whether a key exists and is visible by the current session.
+	Exists(k []byte) (bool, error)
+	// Delete a record by key. If not found, returns ErrKeyNotFound.
+	Delete(k []byte) error
+	DeleteRange(start []byte, end []byte) error
+	Iterator(opts *IterOptions) (Iterator, error)
+}
+
+type Iterator interface {
+	Close() error
+	First() bool
+	Last() bool
+	Valid() bool
+	Next() bool
+	Prev() bool
+	Error() error
+	Key() []byte
+	Value() ([]byte, error)
+}
+
+type IterOptions struct {
+	// LowerBound specifies the smallest key (inclusive) that the iterator will
+	// return during iteration. If the iterator is seeked or iterated past this
+	// boundary the iterator will return Valid()==false. Setting LowerBound
+	// effectively truncates the key space visible to the iterator.
+	LowerBound []byte
+	// UpperBound specifies the largest key (exclusive) that the iterator will
+	// return during iteration. If the iterator is seeked or iterated past this
+	// boundary the iterator will return Valid()==false. Setting UpperBound
+	// effectively truncates the key space visible to the iterator.
+	UpperBound []byte
+}
diff --git a/internal/kv/batch.go b/internal/kv/batch.go
index 7ec5647d..24ffb6eb 100644
--- a/internal/kv/batch.go
+++ b/internal/kv/batch.go
@@ -1,18 +1,19 @@
 package kv
 
 import (
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble"
 )
 
-var _ Session = (*BatchSession)(nil)
+var _ engine.Session = (*BatchSession)(nil)
 
 var (
 	tombStone = []byte{0}
 )
 
 type BatchSession struct {
-	Store           *Store
+	Store           *PebbleEngine
 	DB              *pebble.DB
 	Batch           *pebble.Batch
 	closed          bool
@@ -21,7 +22,7 @@ type BatchSession struct {
 	keys            map[string]struct{}
 }
 
-func (s *Store) NewBatchSession() *BatchSession {
+func (s *PebbleEngine) NewBatchSession() engine.Session {
 	// before creating a batch session, create a shared snapshot
 	// at this point-in-time.
 	s.LockSharedSnapshot()
@@ -142,7 +143,7 @@ func (s *BatchSession) Insert(k, v []byte) error {
 		return err
 	}
 	if ok {
-		return ErrKeyAlreadyExists
+		return engine.ErrKeyAlreadyExists
 	}
 
 	s.keys[string(k)] = struct{}{}
@@ -190,7 +191,7 @@ func (s *BatchSession) Delete(k []byte) error {
 // DeleteRange deletes all keys in the given range.
 // This implementation deletes all keys one by one to simplify the rollback.
 func (s *BatchSession) DeleteRange(start []byte, end []byte) error {
-	it, err := s.Iterator(&IterOptions{
+	it, err := s.Iterator(&engine.IterOptions{
 		LowerBound: start,
 		UpperBound: end,
 	})
@@ -209,7 +210,7 @@ func (s *BatchSession) DeleteRange(start []byte, end []byte) error {
 	return nil
 }
 
-func (s *BatchSession) Iterator(opts *IterOptions) (Iterator, error) {
+func (s *BatchSession) Iterator(opts *engine.IterOptions) (engine.Iterator, error) {
 	err := s.applyBatch()
 	if err != nil {
 		return nil, err
diff --git a/internal/kv/store.go b/internal/kv/engine.go
similarity index 87%
rename from internal/kv/store.go
rename to internal/kv/engine.go
index 4156adb9..aa37b265 100644
--- a/internal/kv/store.go
+++ b/internal/kv/engine.go
@@ -20,7 +20,7 @@ const (
 	defaultMaxTransientBatchSize int = 1 << 19          // 512KB
 )
 
-type Store struct {
+type PebbleEngine struct {
 	db              *pebble.DB
 	opts            Options
 	rollbackSegment *RollbackSegment
@@ -47,7 +47,7 @@ type Options struct {
 	MaxTransientNamespace    uint64
 }
 
-func NewEngineWith(path string, opts Options, popts *pebble.Options) (*Store, error) {
+func NewEngineWith(path string, opts Options, popts *pebble.Options) (*PebbleEngine, error) {
 	if popts == nil {
 		popts = &pebble.Options{}
 	}
@@ -68,7 +68,7 @@ func NewEngineWith(path string, opts Options, popts *pebble.Options) (*Store, er
 	return NewStore(db, opts), nil
 }
 
-func NewEngine(path string, opts Options) (*Store, error) {
+func NewEngine(path string, opts Options) (*PebbleEngine, error) {
 	var popts pebble.Options
 	var pbpath string
 
@@ -116,7 +116,7 @@ var DefaultComparer = &pebble.Comparer{
 	Name: "leveldb.BytewiseComparator",
 }
 
-func NewStore(db *pebble.DB, opts Options) *Store {
+func NewStore(db *pebble.DB, opts Options) *PebbleEngine {
 	if opts.MaxBatchSize <= 0 {
 		opts.MaxBatchSize = defaultMaxBatchSize
 	}
@@ -130,26 +130,26 @@ func NewStore(db *pebble.DB, opts Options) *Store {
 		panic("max transient namespace cannot be 0")
 	}
 
-	return &Store{
+	return &PebbleEngine{
 		db:              db,
 		opts:            opts,
 		rollbackSegment: NewRollbackSegment(db, opts.RollbackSegmentNamespace),
 	}
 }
 
-func (s *Store) Close() error {
+func (s *PebbleEngine) Close() error {
 	return s.db.Close()
 }
 
-func (s *Store) Rollback() error {
+func (s *PebbleEngine) Rollback() error {
 	return s.rollbackSegment.Rollback()
 }
 
-func (s *Store) ResetRollbackSegment() error {
+func (s *PebbleEngine) Recover() error {
 	return s.rollbackSegment.Reset()
 }
 
-func (s *Store) LockSharedSnapshot() {
+func (s *PebbleEngine) LockSharedSnapshot() {
 	s.sharedSnapshot.Lock()
 	s.sharedSnapshot.snapshot = &snapshot{
 		snapshot: s.db.NewSnapshot(),
@@ -159,18 +159,18 @@ func (s *Store) LockSharedSnapshot() {
 	s.sharedSnapshot.Unlock()
 }
 
-func (s *Store) UnlockSharedSnapshot() {
+func (s *PebbleEngine) UnlockSharedSnapshot() {
 	s.sharedSnapshot.Lock()
 	s.sharedSnapshot.snapshot.Done()
 	s.sharedSnapshot.snapshot = nil
 	s.sharedSnapshot.Unlock()
 }
 
-func (s *Store) DB() *pebble.DB {
+func (s *PebbleEngine) DB() *pebble.DB {
 	return s.db
 }
 
-func (s *Store) CleanupTransientNamespaces() error {
+func (s *PebbleEngine) CleanupTransientNamespaces() error {
 	return s.db.DeleteRange(
 		encoding.EncodeUint(nil, uint64(s.minTransientNamespace)),
 		encoding.EncodeUint(nil, uint64(s.maxTransientNamespace)),
diff --git a/internal/kv/session.go b/internal/kv/session.go
index 4bcf1eda..895e20a7 100644
--- a/internal/kv/session.go
+++ b/internal/kv/session.go
@@ -1,61 +1,11 @@
 package kv
 
 import (
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble"
 )
 
-// Common errors returned by the engine.
-var (
-	// ErrKeyNotFound is returned when the targeted key doesn't exist.
-	ErrKeyNotFound = errors.New("key not found")
-
-	// ErrKeyAlreadyExists is returned when the targeted key already exists.
-	ErrKeyAlreadyExists = errors.New("key already exists")
-)
-
-type Session interface {
-	Commit() error
-	Close() error
-	// Insert inserts a key-value pair. If it already exists, it returns ErrKeyAlreadyExists.
-	Insert(k, v []byte) error
-	// Put stores a key-value pair. If it already exists, it overrides it.
-	Put(k, v []byte) error
-	// Get returns a value associated with the given key. If not found, returns ErrKeyNotFound.
-	Get(k []byte) ([]byte, error)
-	// Exists returns whether a key exists and is visible by the current session.
-	Exists(k []byte) (bool, error)
-	// Delete a record by key. If not found, returns ErrKeyNotFound.
-	Delete(k []byte) error
-	DeleteRange(start []byte, end []byte) error
-	Iterator(opts *IterOptions) (Iterator, error)
-}
-
-type Iterator interface {
-	Close() error
-	First() bool
-	Last() bool
-	Valid() bool
-	Next() bool
-	Prev() bool
-	Error() error
-	Key() []byte
-	Value() ([]byte, error)
-}
-
-type IterOptions struct {
-	// LowerBound specifies the smallest key (inclusive) that the iterator will
-	// return during iteration. If the iterator is seeked or iterated past this
-	// boundary the iterator will return Valid()==false. Setting LowerBound
-	// effectively truncates the key space visible to the iterator.
-	LowerBound []byte
-	// UpperBound specifies the largest key (exclusive) that the iterator will
-	// return during iteration. If the iterator is seeked or iterated past this
-	// boundary the iterator will return Valid()==false. Setting UpperBound
-	// effectively truncates the key space visible to the iterator.
-	UpperBound []byte
-}
-
 type iterator struct {
 	*pebble.Iterator
 }
@@ -69,7 +19,7 @@ func get(r pebble.Reader, k []byte) ([]byte, error) {
 	value, closer, err := r.Get(k)
 	if err != nil {
 		if errors.Is(err, pebble.ErrNotFound) {
-			return nil, errors.WithStack(ErrKeyNotFound)
+			return nil, errors.WithStack(engine.ErrKeyNotFound)
 		}
 
 		return nil, err
diff --git a/internal/kv/session_test.go b/internal/kv/session_test.go
index e6a4b839..60ba3be9 100644
--- a/internal/kv/session_test.go
+++ b/internal/kv/session_test.go
@@ -7,13 +7,13 @@ import (
 
 	"github.com/chaisql/chai"
 	"github.com/chaisql/chai/internal/encoding"
-	"github.com/chaisql/chai/internal/kv"
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/chaisql/chai/internal/testutil"
 	"github.com/chaisql/chai/internal/testutil/assert"
 	"github.com/stretchr/testify/require"
 )
 
-func getValue(t *testing.T, st kv.Session, key []byte) []byte {
+func getValue(t *testing.T, st engine.Session, key []byte) []byte {
 	v, err := st.Get([]byte(key))
 	assert.NoError(t, err)
 	return v
@@ -44,7 +44,7 @@ func TestReadOnly(t *testing.T) {
 	})
 }
 
-func kvBuilder(t testing.TB) kv.Session {
+func kvBuilder(t testing.TB) engine.Session {
 	ng := testutil.NewEngine(t)
 	s := ng.NewBatchSession()
 
@@ -121,7 +121,7 @@ func TestRollback(t *testing.T) {
 	for i := int64(9); i >= 0; i-- {
 		key := encoding.EncodeInt(encoding.EncodeInt(nil, 10), i)
 		_, err = snapshot.Get(key)
-		require.ErrorIs(t, err, kv.ErrKeyNotFound)
+		require.ErrorIs(t, err, engine.ErrKeyNotFound)
 	}
 }
 
@@ -181,7 +181,7 @@ func TestStoreGet(t *testing.T) {
 		st := kvBuilder(t)
 
 		r, err := st.Get(foo)
-		assert.ErrorIs(t, err, kv.ErrKeyNotFound)
+		assert.ErrorIs(t, err, engine.ErrKeyNotFound)
 		require.Nil(t, r)
 	})
 
diff --git a/internal/kv/snapshot.go b/internal/kv/snapshot.go
index a61535ca..717e6fc5 100644
--- a/internal/kv/snapshot.go
+++ b/internal/kv/snapshot.go
@@ -3,6 +3,7 @@ package kv
 import (
 	"math"
 
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/chaisql/chai/internal/pkg/atomic"
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble"
@@ -25,14 +26,14 @@ func (s *snapshot) Done() error {
 }
 
 type SnapshotSession struct {
-	Store    *Store
+	Store    *PebbleEngine
 	Snapshot *snapshot
 	closed   bool
 }
 
-var _ Session = (*SnapshotSession)(nil)
+var _ engine.Session = (*SnapshotSession)(nil)
 
-func (s *Store) NewSnapshotSession() *SnapshotSession {
+func (s *PebbleEngine) NewSnapshotSession() engine.Session {
 	var sn *snapshot
 
 	// if there is a shared snapshot, use it.
@@ -96,7 +97,7 @@ func (s *SnapshotSession) DeleteRange(start []byte, end []byte) error {
 	return errors.New("cannot delete range in read-only mode")
 }
 
-func (s *SnapshotSession) Iterator(opts *IterOptions) (Iterator, error) {
+func (s *SnapshotSession) Iterator(opts *engine.IterOptions) (engine.Iterator, error) {
 	var popts *pebble.IterOptions
 	if opts != nil {
 		popts = &pebble.IterOptions{
diff --git a/internal/kv/transient.go b/internal/kv/transient.go
index 7ae038d0..ae32c8b6 100644
--- a/internal/kv/transient.go
+++ b/internal/kv/transient.go
@@ -1,21 +1,22 @@
 package kv
 
 import (
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble"
 )
 
-var _ Session = (*TransientSession)(nil)
+var _ engine.Session = (*TransientSession)(nil)
 
 type TransientSession struct {
 	db           *pebble.DB
 	batch        *pebble.Batch
-	store        *Store
+	store        *PebbleEngine
 	maxBatchSize int
 	closed       bool
 }
 
-func (s *Store) NewTransientSession() *TransientSession {
+func (s *PebbleEngine) NewTransientSession() engine.Session {
 	return &TransientSession{
 		db:           s.db,
 		maxBatchSize: s.opts.MaxTransientBatchSize,
@@ -69,7 +70,7 @@ func (s *TransientSession) Put(k, v []byte) error {
 // Get returns a value associated with the given key. If not found, returns ErrKeyNotFound.
 func (s *TransientSession) Get(k []byte) ([]byte, error) {
 	if s.batch == nil {
-		return nil, errors.WithStack(ErrKeyNotFound)
+		return nil, errors.WithStack(engine.ErrKeyNotFound)
 	}
 
 	return get(s.batch, k)
@@ -87,13 +88,13 @@ func (s *TransientSession) Exists(k []byte) (bool, error) {
 // Delete a record by key. If not found, returns ErrKeyNotFound.
 func (s *TransientSession) Delete(k []byte) error {
 	if s.batch == nil {
-		return errors.WithStack(ErrKeyNotFound)
+		return errors.WithStack(engine.ErrKeyNotFound)
 	}
 
 	_, closer, err := s.batch.Get(k)
 	if err != nil {
 		if errors.Is(err, pebble.ErrNotFound) {
-			return errors.WithStack(ErrKeyNotFound)
+			return errors.WithStack(engine.ErrKeyNotFound)
 		}
 
 		return err
@@ -114,7 +115,7 @@ func (s *TransientSession) DeleteRange(start []byte, end []byte) error {
 	return s.batch.DeleteRange(start, end, nil)
 }
 
-func (s *TransientSession) Iterator(opts *IterOptions) (Iterator, error) {
+func (s *TransientSession) Iterator(opts *engine.IterOptions) (engine.Iterator, error) {
 	var popts *pebble.IterOptions
 	if opts != nil {
 		popts = &pebble.IterOptions{
diff --git a/internal/stream/rows/temp_tree_sort.go b/internal/stream/rows/temp_tree_sort.go
index c0841b6d..37cf497a 100644
--- a/internal/stream/rows/temp_tree_sort.go
+++ b/internal/stream/rows/temp_tree_sort.go
@@ -36,7 +36,7 @@ func (op *TempTreeSortOperator) Iterate(in *environment.Environment, fn func(out
 
 	catalog := in.GetTx().Catalog
 	tns := catalog.GetFreeTransientNamespace()
-	tr, cleanup, err := tree.NewTransient(db.Store.NewTransientSession(), tns, 0)
+	tr, cleanup, err := tree.NewTransient(db.Engine.NewTransientSession(), tns, 0)
 	if err != nil {
 		return err
 	}
diff --git a/internal/stream/union.go b/internal/stream/union.go
index cf812360..eb99b8ff 100644
--- a/internal/stream/union.go
+++ b/internal/stream/union.go
@@ -56,7 +56,7 @@ func (it *UnionOperator) Iterate(in *environment.Environment, fn func(out *envir
 				// create a temporary tree
 				db := in.GetDB()
 				tns := in.GetTx().Catalog.GetFreeTransientNamespace()
-				temp, cleanup, err = tree.NewTransient(db.Store.NewTransientSession(), tns, 0)
+				temp, cleanup, err = tree.NewTransient(db.Engine.NewTransientSession(), tns, 0)
 				if err != nil {
 					return err
 				}
diff --git a/internal/testutil/db.go b/internal/testutil/db.go
index 49693d72..ea899af1 100644
--- a/internal/testutil/db.go
+++ b/internal/testutil/db.go
@@ -16,7 +16,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func NewEngine(t testing.TB) *kv.Store {
+func NewEngine(t testing.TB) *kv.PebbleEngine {
 	t.Helper()
 
 	st, err := kv.NewEngine(":memory:", kv.Options{
diff --git a/internal/tree/tree.go b/internal/tree/tree.go
index 3b68028e..95f986dc 100644
--- a/internal/tree/tree.go
+++ b/internal/tree/tree.go
@@ -6,7 +6,7 @@ import (
 	"time"
 
 	"github.com/chaisql/chai/internal/encoding"
-	"github.com/chaisql/chai/internal/kv"
+	"github.com/chaisql/chai/internal/engine"
 	"github.com/chaisql/chai/internal/types"
 	"github.com/cockroachdb/errors"
 )
@@ -58,12 +58,12 @@ func (o SortOrder) SetAsc(i int) SortOrder {
 // of the types package operators.
 // A Tree doesn't support duplicate keys.
 type Tree struct {
-	Session   kv.Session
+	Session   engine.Session
 	Namespace Namespace
 	Order     SortOrder
 }
 
-func New(session kv.Session, ns Namespace, order SortOrder) *Tree {
+func New(session engine.Session, ns Namespace, order SortOrder) *Tree {
 	return &Tree{
 		Namespace: ns,
 		Session:   session,
@@ -71,7 +71,7 @@ func New(session kv.Session, ns Namespace, order SortOrder) *Tree {
 	}
 }
 
-func NewTransient(session kv.Session, ns Namespace, order SortOrder) (*Tree, func() error, error) {
+func NewTransient(session engine.Session, ns Namespace, order SortOrder) (*Tree, func() error, error) {
 	t := Tree{
 		Namespace: ns,
 		Session:   session,
@@ -92,7 +92,7 @@ func NewTransient(session kv.Session, ns Namespace, order SortOrder) (*Tree, fun
 var defaultValue = []byte{0}
 
 // Insert adds a key-obj combination to the tree.
-// If the key already exists, it returns kv.ErrKeyAlreadyExists.
+// If the key already exists, it returns engine.ErrKeyAlreadyExists.
 func (t *Tree) Insert(key *Key, value []byte) error {
 	if len(value) == 0 {
 		value = defaultValue
@@ -121,7 +121,7 @@ func (t *Tree) Put(key *Key, value []byte) error {
 }
 
 // Get a key from the tree. If the key doesn't exist,
-// it returns kv.ErrKeyNotFound.
+// it returns engine.ErrKeyNotFound.
 func (t *Tree) Get(key *Key) ([]byte, error) {
 	k, err := key.Encode(t.Namespace, t.Order)
 	if err != nil {
@@ -142,7 +142,7 @@ func (t *Tree) Exists(key *Key) (bool, error) {
 }
 
 // Delete a key from the tree. If the key doesn't exist,
-// it returns kv.ErrKeyNotFound.
+// it returns engine.ErrKeyNotFound.
 func (t *Tree) Delete(key *Key) error {
 	k, err := key.Encode(t.Namespace, t.Order)
 	if err != nil {
@@ -183,7 +183,7 @@ func (t *Tree) IterateOnRange(rng *Range, reverse bool, fn func(*Key, []byte) er
 		return err
 	}
 
-	opts := kv.IterOptions{
+	opts := engine.IterOptions{
 		LowerBound: start,
 		UpperBound: end,
 	}