diff --git a/backend/cmd/sink/main.go b/backend/cmd/sink/main.go
index 84520dd33..a7e2804c4 100644
--- a/backend/cmd/sink/main.go
+++ b/backend/cmd/sink/main.go
@@ -32,7 +32,7 @@ func main() {
 		log.Fatalf("%v doesn't exist. %v", cfg.FsDir, err)
 	}
 
-	writer := sessionwriter.NewWriter(cfg.FsUlimit, cfg.FsDir, cfg.DeadSessionTimeout)
+	writer := sessionwriter.NewWriter(cfg.FsUlimit, cfg.FsDir, cfg.FileBuffer, cfg.SyncTimeout)
 
 	producer := queue.NewProducer(cfg.MessageSizeLimit, true)
 	defer producer.Close(cfg.ProducerCloseTimeout)
@@ -95,26 +95,20 @@ func main() {
 			counter.Update(msg.SessionID(), time.UnixMilli(ts))
 		}
 
-		// Write encoded message with index to session file
-		data := msg.EncodeWithIndex()
+		// Try to encode message to avoid null data inserts
+		data := msg.Encode()
 		if data == nil {
 			return
 		}
 
 		// Write message to file
-		if messages.IsDOMType(msg.TypeID()) {
-			if err := writer.WriteDOM(msg.SessionID(), data); err != nil {
-				log.Printf("Writer error: %v\n", err)
-			}
-		}
-		if !messages.IsDOMType(msg.TypeID()) || msg.TypeID() == messages.MsgTimestamp {
-			if err := writer.WriteDEV(msg.SessionID(), data); err != nil {
-				log.Printf("Writer error: %v\n", err)
-			}
+		if err := writer.Write(msg); err != nil {
+			log.Printf("writer error: %s", err)
+			return
 		}
 
 		// [METRICS] Increase the number of written to the files messages and the message size
-		messageSize.Record(context.Background(), float64(len(data)))
+		messageSize.Record(context.Background(), float64(len(msg.Encode())))
 		savedMessages.Add(context.Background(), 1)
 	}
 
@@ -132,7 +126,8 @@ func main() {
 	sigchan := make(chan os.Signal, 1)
 	signal.Notify(sigchan, syscall.SIGINT, syscall.SIGTERM)
 
-	tick := time.Tick(30 * time.Second)
+	tick := time.Tick(10 * time.Second)
+	tickInfo := time.Tick(30 * time.Second)
 	for {
 		select {
 		case sig := <-sigchan:
@@ -146,10 +141,11 @@ func main() {
 			consumer.Close()
 			os.Exit(0)
 		case <-tick:
-			counter.Print()
 			if err := consumer.Commit(); err != nil {
 				log.Printf("can't commit messages: %s", err)
 			}
+		case <-tickInfo:
+			counter.Print()
 			log.Printf("writer: %s", writer.Info())
 		default:
 			err := consumer.ConsumeNext()
diff --git a/backend/internal/config/sink/config.go b/backend/internal/config/sink/config.go
index a8703a596..1a2df142e 100644
--- a/backend/internal/config/sink/config.go
+++ b/backend/internal/config/sink/config.go
@@ -9,7 +9,8 @@ type Config struct {
 	common.Config
 	FsDir                string `env:"FS_DIR,required"`
 	FsUlimit             uint16 `env:"FS_ULIMIT,required"`
-	DeadSessionTimeout   int64  `env:"DEAD_SESSION_TIMEOUT,default=600"`
+	FileBuffer           int    `env:"FILE_BUFFER,default=32768"`
+	SyncTimeout          int    `env:"SYNC_TIMEOUT,default=5"`
 	GroupSink            string `env:"GROUP_SINK,required"`
 	TopicRawWeb          string `env:"TOPIC_RAW_WEB,required"`
 	TopicRawIOS          string `env:"TOPIC_RAW_IOS,required"`
diff --git a/backend/internal/sink/sessionwriter/file.go b/backend/internal/sink/sessionwriter/file.go
new file mode 100644
index 000000000..1ad076d72
--- /dev/null
+++ b/backend/internal/sink/sessionwriter/file.go
@@ -0,0 +1,57 @@
+package sessionwriter
+
+import (
+	"bufio"
+	"os"
+)
+
+type File struct {
+	file    *os.File
+	buffer  *bufio.Writer
+	updated bool
+}
+
+func NewFile(path string, bufSize int) (*File, error) {
+	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
+	if err != nil {
+		return nil, err
+	}
+	return &File{
+		file:    file,
+		buffer:  bufio.NewWriterSize(file, bufSize),
+		updated: false,
+	}, nil
+}
+
+func (f *File) Write(data []byte) error {
+	leftToWrite := len(data)
+	for leftToWrite > 0 {
+		writtenDown, err := f.buffer.Write(data)
+		if err != nil {
+			return err
+		}
+		leftToWrite -= writtenDown
+	}
+	f.updated = true
+	return nil
+}
+
+func (f *File) Sync() error {
+	if !f.updated {
+		return nil
+	}
+	if err := f.buffer.Flush(); err != nil {
+		return err
+	}
+	if err := f.file.Sync(); err != nil {
+		return err
+	}
+	f.updated = false
+	return nil
+}
+
+func (f *File) Close() error {
+	_ = f.buffer.Flush()
+	_ = f.file.Sync()
+	return f.file.Close()
+}
diff --git a/backend/internal/sink/sessionwriter/meta.go b/backend/internal/sink/sessionwriter/meta.go
new file mode 100644
index 000000000..4fac56e50
--- /dev/null
+++ b/backend/internal/sink/sessionwriter/meta.go
@@ -0,0 +1,56 @@
+package sessionwriter
+
+import (
+	"math"
+	"sync"
+	"time"
+)
+
+type Meta struct {
+	limit int
+	lock  *sync.Mutex
+	meta  map[uint64]int64
+}
+
+func NewMeta(limit int) *Meta {
+	return &Meta{
+		limit: limit,
+		lock:  &sync.Mutex{},
+		meta:  make(map[uint64]int64, limit),
+	}
+}
+
+func (m *Meta) Add(sid uint64) {
+	m.lock.Lock()
+	m.meta[sid] = time.Now().Unix()
+	m.lock.Unlock()
+}
+
+func (m *Meta) Count() int {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	return len(m.meta)
+}
+
+func (m *Meta) Delete(sid uint64) {
+	m.lock.Lock()
+	delete(m.meta, sid)
+	m.lock.Unlock()
+}
+
+func (m *Meta) GetExtra() uint64 {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	if len(m.meta) >= m.limit {
+		var extraSessID uint64
+		var minTimestamp int64 = math.MaxInt64
+		for sessID, timestamp := range m.meta {
+			if timestamp < minTimestamp {
+				extraSessID = sessID
+				minTimestamp = timestamp
+			}
+		}
+		return extraSessID
+	}
+	return 0
+}
diff --git a/backend/internal/sink/sessionwriter/session.go b/backend/internal/sink/sessionwriter/session.go
index f107c387b..8cf8881de 100644
--- a/backend/internal/sink/sessionwriter/session.go
+++ b/backend/internal/sink/sessionwriter/session.go
@@ -1,81 +1,96 @@
 package sessionwriter
 
 import (
+	"encoding/binary"
 	"fmt"
-	"os"
 	"strconv"
 	"sync"
-	"time"
+
+	"openreplay/backend/pkg/messages"
 )
 
 type Session struct {
-	lock       *sync.Mutex
-	dom        *os.File
-	dev        *os.File
-	lastUpdate time.Time
+	lock    *sync.Mutex
+	dom     *File
+	dev     *File
+	index   []byte
+	updated bool
 }
 
-func NewSession(dir string, id uint64) (*Session, error) {
-	if id == 0 {
+func NewSession(sessID uint64, workDir string, bufSize int) (*Session, error) {
+	if sessID == 0 {
 		return nil, fmt.Errorf("wrong session id")
 	}
+	filePath := workDir + strconv.FormatUint(sessID, 10)
 
-	filePath := dir + strconv.FormatUint(id, 10)
-	domFile, err := os.OpenFile(filePath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
+	dom, err := NewFile(filePath, bufSize)
 	if err != nil {
 		return nil, err
 	}
-	filePath += "devtools"
-	devFile, err := os.OpenFile(filePath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
+	dev, err := NewFile(filePath+"devtools", bufSize)
 	if err != nil {
-		domFile.Close() // should close first file descriptor
+		dom.Close()
 		return nil, err
 	}
 
 	return &Session{
-		lock:       &sync.Mutex{},
-		dom:        domFile,
-		dev:        devFile,
-		lastUpdate: time.Now(),
+		lock:    &sync.Mutex{},
+		dom:     dom,
+		dev:     dev,
+		index:   make([]byte, 8),
+		updated: false,
 	}, nil
 }
 
-func (s *Session) Lock() {
+func (s *Session) Write(msg messages.Message) error {
 	s.lock.Lock()
-}
+	defer s.lock.Unlock()
 
-func (s *Session) Unlock() {
-	s.lock.Unlock()
-}
+	// Encode message index
+	binary.LittleEndian.PutUint64(s.index, msg.Meta().Index)
 
-func (s *Session) Write(mode FileType, data []byte) (err error) {
-	if mode == DOM {
-		_, err = s.dom.Write(data)
-	} else {
-		_, err = s.dev.Write(data)
+	// Write message to dom.mob file
+	if messages.IsDOMType(msg.TypeID()) {
+		// Write message index
+		if err := s.dom.Write(s.index); err != nil {
+			return err
+		}
+		// Write message body
+		if err := s.dom.Write(msg.Encode()); err != nil {
+			return err
+		}
 	}
-	s.lastUpdate = time.Now()
-	return err
-}
-
-func (s *Session) LastUpdate() time.Time {
-	return s.lastUpdate
+	s.updated = true
+	// Write message to dev.mob file
+	if !messages.IsDOMType(msg.TypeID()) || msg.TypeID() == messages.MsgTimestamp {
+		// Write message index
+		if err := s.dev.Write(s.index); err != nil {
+			return err
+		}
+		// Write message body
+		if err := s.dev.Write(msg.Encode()); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func (s *Session) Sync() error {
-	domErr := s.dom.Sync()
-	devErr := s.dev.Sync()
-	if domErr == nil && devErr == nil {
-		return nil
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	if err := s.dom.Sync(); err != nil {
+		return err
 	}
-	return fmt.Errorf("dom: %s, dev: %s", domErr, devErr)
+	return s.dev.Sync()
 }
 
 func (s *Session) Close() error {
-	domErr := s.dom.Close()
-	devErr := s.dev.Close()
-	if domErr == nil && devErr == nil {
-		return nil
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	if err := s.dom.Close(); err != nil {
+		return err
 	}
-	return fmt.Errorf("dom: %s, dev: %s", domErr, devErr)
+	return s.dev.Close()
 }
diff --git a/backend/internal/sink/sessionwriter/types.go b/backend/internal/sink/sessionwriter/types.go
deleted file mode 100644
index a20f61375..000000000
--- a/backend/internal/sink/sessionwriter/types.go
+++ /dev/null
@@ -1,8 +0,0 @@
-package sessionwriter
-
-type FileType int
-
-const (
-	DOM FileType = 1
-	DEV FileType = 2
-)
diff --git a/backend/internal/sink/sessionwriter/writer.go b/backend/internal/sink/sessionwriter/writer.go
index 94ff5dd66..f2eb052c7 100644
--- a/backend/internal/sink/sessionwriter/writer.go
+++ b/backend/internal/sink/sessionwriter/writer.go
@@ -3,47 +3,89 @@ package sessionwriter
 import (
 	"fmt"
 	"log"
-	"math"
 	"sync"
 	"time"
+
+	"openreplay/backend/pkg/messages"
 )
 
 type SessionWriter struct {
-	ulimit               int
-	dir                  string
-	zombieSessionTimeout float64
-	lock                 *sync.Mutex
-	sessions             *sync.Map
-	meta                 map[uint64]int64
-	done                 chan struct{}
-	stopped              chan struct{}
+	filesLimit  int
+	workingDir  string
+	fileBuffer  int
+	syncTimeout time.Duration
+	meta        *Meta
+	sessions    *sync.Map
+	done        chan struct{}
+	stopped     chan struct{}
 }
 
-func NewWriter(ulimit uint16, dir string, zombieSessionTimeout int64) *SessionWriter {
+func NewWriter(filesLimit uint16, workingDir string, fileBuffer int, syncTimeout int) *SessionWriter {
 	w := &SessionWriter{
-		ulimit:               int(ulimit) / 2, // should divide by 2 because each session has 2 files
-		dir:                  dir + "/",
-		zombieSessionTimeout: float64(zombieSessionTimeout),
-		lock:                 &sync.Mutex{},
-		sessions:             &sync.Map{},
-		meta:                 make(map[uint64]int64, ulimit),
-		done:                 make(chan struct{}),
-		stopped:              make(chan struct{}),
+		filesLimit:  int(filesLimit) / 2, // should divide by 2 because each session has 2 files
+		workingDir:  workingDir + "/",
+		fileBuffer:  fileBuffer,
+		syncTimeout: time.Duration(syncTimeout) * time.Second,
+		meta:        NewMeta(int(filesLimit)),
+		sessions:    &sync.Map{},
+		done:        make(chan struct{}),
+		stopped:     make(chan struct{}),
 	}
 	go w.synchronizer()
 	return w
 }
 
-func (w *SessionWriter) WriteDOM(sid uint64, data []byte) error {
-	return w.write(sid, DOM, data)
+func (w *SessionWriter) Write(msg messages.Message) (err error) {
+	var (
+		sess *Session
+		sid  = msg.SessionID()
+	)
+
+	// Load session
+	sessObj, ok := w.sessions.Load(sid)
+	if !ok {
+		// Create new session
+		sess, err = NewSession(sid, w.workingDir, w.fileBuffer)
+		if err != nil {
+			return fmt.Errorf("can't create session: %d, err: %s", sid, err)
+		}
+
+		// Check opened sessions limit and close extra session if you need to
+		if extraSessID := w.meta.GetExtra(); extraSessID != 0 {
+			if err := w.Close(extraSessID); err != nil {
+				log.Printf("can't close session: %s", err)
+			}
+		}
+
+		// Add created session
+		w.sessions.Store(sid, sess)
+		w.meta.Add(sid)
+	} else {
+		sess = sessObj.(*Session)
+	}
+
+	// Write data to session
+	return sess.Write(msg)
 }
 
-func (w *SessionWriter) WriteDEV(sid uint64, data []byte) error {
-	return w.write(sid, DEV, data)
+func (w *SessionWriter) sync(sid uint64) error {
+	sessObj, ok := w.sessions.Load(sid)
+	if !ok {
+		return fmt.Errorf("session: %d not found", sid)
+	}
+	sess := sessObj.(*Session)
+	return sess.Sync()
 }
 
-func (w *SessionWriter) Close(sid uint64) {
-	w.close(sid)
+func (w *SessionWriter) Close(sid uint64) error {
+	sessObj, ok := w.sessions.LoadAndDelete(sid)
+	if !ok {
+		return fmt.Errorf("session: %d not found", sid)
+	}
+	sess := sessObj.(*Session)
+	err := sess.Close()
+	w.meta.Delete(sid)
+	return err
 }
 
 func (w *SessionWriter) Stop() {
@@ -52,110 +94,11 @@ func (w *SessionWriter) Stop() {
 }
 
 func (w *SessionWriter) Info() string {
-	return fmt.Sprintf("%d sessions", w.numberOfSessions())
-}
-
-func (w *SessionWriter) addSession(sid uint64) {
-	w.lock.Lock()
-	w.meta[sid] = time.Now().Unix()
-	w.lock.Unlock()
-}
-
-func (w *SessionWriter) deleteSession(sid uint64) {
-	w.lock.Lock()
-	delete(w.meta, sid)
-	w.lock.Unlock()
-}
-
-func (w *SessionWriter) numberOfSessions() int {
-	w.lock.Lock()
-	defer w.lock.Unlock()
-	return len(w.meta)
-}
-
-func (w *SessionWriter) write(sid uint64, mode FileType, data []byte) error {
-	var (
-		sess *Session
-		err  error
-	)
-
-	sessObj, ok := w.sessions.Load(sid)
-	if !ok {
-		sess, err = NewSession(w.dir, sid)
-		if err != nil {
-			return fmt.Errorf("can't write to session: %d, err: %s", sid, err)
-		}
-		sess.Lock()
-		defer sess.Unlock()
-
-		// Check opened files limit
-		if len(w.meta) >= w.ulimit {
-			var oldSessID uint64
-			var minTimestamp int64 = math.MaxInt64
-			for sessID, timestamp := range w.meta {
-				if timestamp < minTimestamp {
-					oldSessID = sessID
-					minTimestamp = timestamp
-				}
-			}
-			if err := w.close(oldSessID); err != nil {
-				log.Printf("can't close session: %s", err)
-			}
-		}
-
-		// Add new session to manager
-		w.sessions.Store(sid, sess)
-		w.addSession(sid)
-	} else {
-		sess = sessObj.(*Session)
-		sess.Lock()
-		defer sess.Unlock()
-	}
-
-	// Write data to session
-	return sess.Write(mode, data)
-}
-
-func (w *SessionWriter) sync(sid uint64) error {
-	sessObj, ok := w.sessions.Load(sid)
-	if !ok {
-		return fmt.Errorf("can't sync, session: %d not found", sid)
-	}
-	sess := sessObj.(*Session)
-	sess.Lock()
-	defer sess.Unlock()
-
-	err := sess.Sync()
-	if time.Now().Sub(sess.LastUpdate()).Seconds() > w.zombieSessionTimeout {
-		if err != nil {
-			log.Printf("can't sync session: %d, err: %s", sid, err)
-		}
-		// Close "zombie" session
-		err = sess.Close()
-		w.deleteSession(sid)
-	}
-	return err
-}
-
-func (w *SessionWriter) close(sid uint64) error {
-	sessObj, ok := w.sessions.LoadAndDelete(sid)
-	if !ok {
-		return fmt.Errorf("can't close, session: %d not found", sid)
-	}
-	sess := sessObj.(*Session)
-	sess.Lock()
-	defer sess.Unlock()
-
-	if err := sess.Sync(); err != nil {
-		log.Printf("can't sync session: %d, err: %s", sid, err)
-	}
-	err := sess.Close()
-	w.deleteSession(sid)
-	return err
+	return fmt.Sprintf("%d sessions", w.meta.Count())
 }
 
 func (w *SessionWriter) synchronizer() {
-	tick := time.Tick(2 * time.Second)
+	tick := time.Tick(w.syncTimeout)
 	for {
 		select {
 		case <-tick:
@@ -167,7 +110,7 @@ func (w *SessionWriter) synchronizer() {
 			})
 		case <-w.done:
 			w.sessions.Range(func(sid, lockObj any) bool {
-				if err := w.close(sid.(uint64)); err != nil {
+				if err := w.Close(sid.(uint64)); err != nil {
 					log.Printf("can't close file descriptor: %s", err)
 				}
 				return true
diff --git a/backend/pkg/messages/iterator.go b/backend/pkg/messages/iterator.go
index 8b23cb97e..7b7991b19 100644
--- a/backend/pkg/messages/iterator.go
+++ b/backend/pkg/messages/iterator.go
@@ -100,6 +100,7 @@ func (i *messageIteratorImpl) Iterate(batchData []byte, batchInfo *BatchInfo) {
 				tp:      msgType,
 				size:    i.size,
 				reader:  reader,
+				raw:     batchData,
 				skipped: &i.canSkip,
 				broken:  &i.broken,
 				meta:    i.messageInfo,
diff --git a/backend/pkg/messages/primitives.go b/backend/pkg/messages/primitives.go
index eb65ae7b1..1d3d2410b 100644
--- a/backend/pkg/messages/primitives.go
+++ b/backend/pkg/messages/primitives.go
@@ -8,13 +8,17 @@ import (
 	"log"
 )
 
+var (
+	one   = []byte{0}
+	three = []byte{0, 0, 0}
+)
+
 func ReadByte(reader io.Reader) (byte, error) {
-	p := make([]byte, 1)
-	_, err := io.ReadFull(reader, p)
+	_, err := io.ReadFull(reader, one)
 	if err != nil {
 		return 0, err
 	}
-	return p[0], nil
+	return one[0], nil
 }
 
 func ReadData(reader io.Reader) ([]byte, error) {
@@ -156,8 +160,7 @@ func WriteSize(size uint64, buf []byte, p int) {
 }
 
 func ReadSize(reader io.Reader) (uint64, error) {
-	buf := make([]byte, 3)
-	n, err := io.ReadFull(reader, buf)
+	n, err := io.ReadFull(reader, three)
 	if err != nil {
 		return 0, err
 	}
@@ -165,7 +168,7 @@ func ReadSize(reader io.Reader) (uint64, error) {
 		return 0, fmt.Errorf("read only %d of 3 size bytes", n)
 	}
 	var size uint64
-	for i, b := range buf {
+	for i, b := range three {
 		size += uint64(b) << (8 * i)
 	}
 	return size, nil
diff --git a/backend/pkg/messages/raw.go b/backend/pkg/messages/raw.go
index 33419d115..dbc71f4e6 100644
--- a/backend/pkg/messages/raw.go
+++ b/backend/pkg/messages/raw.go
@@ -13,6 +13,7 @@ type RawMessage struct {
 	size    uint64
 	data    []byte
 	reader  *bytes.Reader
+	raw     []byte
 	meta    *message
 	encoded bool
 	skipped *bool
@@ -23,15 +24,25 @@ func (m *RawMessage) Encode() []byte {
 	if m.encoded {
 		return m.data
 	}
-	m.data = make([]byte, m.size+1)
-	m.data[0] = uint8(m.tp)
-	m.encoded = true
-	*m.skipped = false
-	_, err := io.ReadFull(m.reader, m.data[1:])
-	if err != nil {
-		log.Printf("message encode err: %s, type: %d, sess: %d", err, m.tp, m.SessionID())
+	// Try to avoid EOF error
+	if m.reader.Len() < int(m.size) {
 		return nil
 	}
+	// Get current batch position
+	currPos, err := m.reader.Seek(0, io.SeekCurrent)
+	if err != nil {
+		log.Printf("can't get current batch position: %s", err)
+		return nil
+	}
+	// "Move" message type
+	if currPos == 0 {
+		log.Printf("can't move message type, curr position = %d", currPos)
+		return nil
+	}
+	// Dirty hack to avoid extra memory allocation
+	m.raw[currPos-1] = uint8(m.tp)
+	m.data = m.raw[currPos-1 : currPos+int64(m.size)]
+	m.encoded = true
 	return m.data
 }