diff --git a/internal/datanode/flush_manager.go b/internal/datanode/flush_manager.go
index 6dfc33db40..9161af08c8 100644
--- a/internal/datanode/flush_manager.go
+++ b/internal/datanode/flush_manager.go
@@ -349,6 +349,11 @@ func (m *rendezvousFlushManager) flushBufferData(data *BufferData, segmentID Uni
 	if err != nil {
 		return err
 	}
+	// get memory size of buffer data
+	fieldMemorySize := make(map[int64]int)
+	for fieldID, fieldData := range data.buffer.Data {
+		fieldMemorySize[fieldID] = fieldData.GetMemorySize()
+	}
 
 	// encode data and convert output data
 	inCodec := storage.NewInsertCodec(meta)
@@ -385,7 +390,7 @@ func (m *rendezvousFlushManager) flushBufferData(data *BufferData, segmentID Uni
 			TimestampFrom: 0, //TODO
 			TimestampTo:   0, //TODO,
 			LogPath:       key,
-			LogSize:       int64(len(blob.Value)),
+			LogSize:       int64(fieldMemorySize[fieldID]),
 		}
 		field2Logidx[fieldID] = logidx
 	}
diff --git a/internal/indexnode/task.go b/internal/indexnode/task.go
index cc3e27c80a..b3cb9b546a 100644
--- a/internal/indexnode/task.go
+++ b/internal/indexnode/task.go
@@ -467,6 +467,12 @@ func (it *IndexBuildTask) buildIndex(ctx context.Context) ([]*storage.Blob, erro
 	}
 	it.tr.Record("index serialize done")
 
+	// use serialized size before encoding
+	it.serializedSize = 0
+	for _, blob := range indexBlobs {
+		it.serializedSize += uint64(len(blob.Value))
+	}
+
 	// early release index for gc, and we can ensure that Delete is idempotent.
 	if err := it.index.Delete(); err != nil {
 		log.Error("IndexNode IndexBuildTask Execute CIndexDelete failed",
@@ -498,10 +504,6 @@ func (it *IndexBuildTask) buildIndex(ctx context.Context) ([]*storage.Blob, erro
 
 func (it *IndexBuildTask) saveIndex(ctx context.Context, blobs []*storage.Blob) error {
 	blobCnt := len(blobs)
-	it.serializedSize = 0
-	for i := range blobs {
-		it.serializedSize += uint64(len(blobs[i].Value))
-	}
 
 	getSavePathByKey := func(key string) string {
 		return path.Join(Params.IndexNodeCfg.IndexStorageRootPath, strconv.Itoa(int(it.req.IndexBuildID)), strconv.Itoa(int(it.req.Version)),