diff --git a/pkg/mdb2/cache.go b/pkg/mdb2/cache.go
index b0678ef..a79af8c 100644
--- a/pkg/mdb2/cache.go
+++ b/pkg/mdb2/cache.go
@@ -2,6 +2,7 @@ package mdb2
 
 import (
 	"fmt"
+	"go.mongodb.org/mongo-driver/bson/bsoncodec"
 	"io/ioutil"
 	"os"
 	"runtime"
@@ -19,7 +20,9 @@ type cache struct {
 	sync.Mutex
 }
 
-func newCache(mdb *Mdb) (*cache, error) {
+var codecRegistry *bsoncodec.Registry
+
+func newCache(mdb *Mdb, registry *bsoncodec.Registry) (*cache, error) {
 	if err := os.MkdirAll(mdb.cacheDir, os.ModePerm); err != nil {
 		return nil, err
 	}
@@ -27,6 +30,8 @@ func newCache(mdb *Mdb) (*cache, error) {
 		m:   make(map[string]*cacheItem),
 		mdb: mdb,
 	}
+
+	codecRegistry = registry
 	c.init()
 	return c, nil
 }
@@ -56,7 +61,7 @@ func (c *cache) init() {
 		}
 		// deserialize to get Id in appropriate type
 		o := &obj{}
-		if err := bson.Unmarshal(raw, o); err == nil {
+		if err := bson.UnmarshalWithRegistry(codecRegistry, raw, o); err == nil {
 			id = o.Id
 		}
 
@@ -126,7 +131,7 @@ func (c *cache) purge() {
 		delete(c.m, k)
 		c.Unlock()
 		err := c.mdb.saveId(i.col, "saveId", i.id, i.o())
-		if err != nil {
+		if err != nil && !IsUnackWrite(err) {
 			log.S("col", i.col).S("id", fmt.Sprintf("%v", i.id)).Error(err)
 		}
 		c.Lock()
@@ -134,7 +139,7 @@ func (c *cache) purge() {
 			c.Unlock()
 			continue
 		}
-		if err == nil {
+		if err == nil || IsUnackWrite(err) {
 			// remove from disk
 			err2 := os.Remove(i.fn)
 			if err2 != nil {
@@ -175,5 +180,5 @@ func (i *cacheItem) o() *bson.Raw {
 }
 
 func (i *cacheItem) unmarshal(o interface{}) error {
-	return bson.Unmarshal(i.raw, o)
+	return bson.UnmarshalWithRegistry(codecRegistry, i.raw, o)
 }
diff --git a/pkg/mdb2/mdb.go b/pkg/mdb2/mdb.go
index 0605ab6..6933a2c 100644
--- a/pkg/mdb2/mdb.go
+++ b/pkg/mdb2/mdb.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"go.mongodb.org/mongo-driver/x/mongo/driver"
 	"reflect"
 	"strings"
 	"text/template"
@@ -219,7 +220,7 @@ func (mdb *Mdb) Init(connStr string, opts ...func(db *Mdb)) error {
 	}
 
 	if mdb.cacheDir != "" {
-		mdb.cache, err = newCache(mdb)
+		mdb.cache, err = newCache(mdb, reg)
 		if err != nil {
 			return err
 		}
@@ -548,3 +549,14 @@ func IsDup(err error) bool {
 	}
 	return false
 }
+
+// IsUnackWrite checks if error is unacknowledged write error
+func IsUnackWrite(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	return errors.Is(err, mongo.ErrUnacknowledgedWrite) ||
+		errors.Is(err, driver.ErrUnacknowledgedWrite) ||
+		err.Error() == mongo.ErrUnacknowledgedWrite.Error()
+}
diff --git a/pkg/mdb2/mdb_test.go b/pkg/mdb2/mdb_test.go
index 3bf8d57..a727ae2 100644
--- a/pkg/mdb2/mdb_test.go
+++ b/pkg/mdb2/mdb_test.go
@@ -5,6 +5,7 @@ import (
 	"encoding/gob"
 	"encoding/json"
 	"fmt"
+	"go.mongodb.org/mongo-driver/bson"
 	"io/ioutil"
 	"os"
 	"reflect"
@@ -57,7 +58,7 @@ var testCacheDir = "./tmp/cacheDir"
 
 func TestCacheAdd(t *testing.T) {
 	db := &Mdb{name: "dbName", cacheDir: testCacheDir}
-	c, err := newCache(db)
+	c, err := newCache(db, bson.DefaultRegistry)
 	assert.Nil(t, err)
 
 	err = c.add("obj", 1, &obj{Id: 1})
@@ -71,7 +72,7 @@ func TestCacheAdd(t *testing.T) {
 	assert.Equal(t, []string{"obj.1", "obj.2", "obj.3"}, ls)
 	t.Logf("%v", ls)
 
-	c2, err := newCache(db)
+	c2, err := newCache(db, bson.DefaultRegistry)
 	assert.Nil(t, err)
 	assert.Len(t, c2.m, 3)
 
@@ -166,3 +167,32 @@ func TestMongoSerde(t *testing.T) {
 	assert.Equal(t, int(m["b"].(map[string]interface{})["i32"].(int32)), res["b"].(map[string]interface{})["i32"])
 	assert.Equal(t, int64(m["c"].(int)), res["c"])
 }
+
+func TestMongoCacheSerde(t *testing.T) {
+	db := &db2{}
+	if err := db.Init(DefaultConnStr(), Name(testDbName), CacheRoot("./tmp/tests/cache")); err != nil {
+		log.Fatalf("failed to open connection: %s", err)
+		return
+	}
+	m := map[string]interface{}{
+		"a": 12345,
+		"b": map[string]interface{}{
+			"i":   12345678901235,
+			"i64": int64(12345678901235),
+			"i32": int32(1234567),
+		},
+		"c": 12345678901234,
+	}
+	db.SaveId(testCollectionName, 2513, m)
+
+	var res map[string]interface{}
+	db.ReadId(testCollectionName, 2513, &res)
+
+	assert.Equal(t, m["a"], res["a"])
+	assert.Equal(t, int64(m["b"].(map[string]interface{})["i"].(int)), res["b"].(map[string]interface{})["i"])
+	assert.Equal(t, m["b"].(map[string]interface{})["i64"].(int64), res["b"].(map[string]interface{})["i64"])
+	assert.Equal(t, int(m["b"].(map[string]interface{})["i32"].(int32)), res["b"].(map[string]interface{})["i32"])
+	assert.Equal(t, int64(m["c"].(int)), res["c"])
+
+	db.cache.purge()
+}