diff --git a/weed/filer2/filechunks.go b/weed/filer2/filechunks.go
index b248a8c59..7fd4af5df 100644
--- a/weed/filer2/filechunks.go
+++ b/weed/filer2/filechunks.go
@@ -3,7 +3,6 @@ package filer2
 import (
 	"fmt"
 	"hash/fnv"
-	"math"
 	"sort"
 
 	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
@@ -103,137 +102,54 @@ func logPrintf(name string, visibles []*visibleInterval) {
 	*/
 }
 
-func nonOverlappingVisibleIntervals(chunks []*filer_pb.FileChunk) (visibles []*visibleInterval) {
-
-	sort.Slice(chunks, func(i, j int) bool {
-		if chunks[i].Offset < chunks[j].Offset {
-			return true
-		}
-		if chunks[i].Offset == chunks[j].Offset {
-			return chunks[i].Mtime < chunks[j].Mtime
-		}
-		return false
-	})
-
-	if len(chunks) == 0 {
-		return
-	}
-
-	var parallelIntervals, intervals []*visibleInterval
-	var minStopInterval, upToDateInterval *visibleInterval
-	watermarkStart := chunks[0].Offset
-	for _, chunk := range chunks {
-		// log.Printf("checking chunk: [%d,%d)", chunk.Offset, chunk.Offset+int64(chunk.Size))
-		logPrintf("parallelIntervals", parallelIntervals)
-		for len(parallelIntervals) > 0 && watermarkStart < chunk.Offset {
-			logPrintf("parallelIntervals loop 1", parallelIntervals)
-			logPrintf("parallelIntervals loop 1 intervals", intervals)
-			minStopInterval, upToDateInterval = findMinStopInterval(parallelIntervals)
-			nextStop := min(minStopInterval.stop, chunk.Offset)
-			intervals = append(intervals, newVisibleInterval(
-				max(watermarkStart, minStopInterval.start),
-				nextStop,
-				upToDateInterval.fileId,
-				upToDateInterval.modifiedTime,
+func mergeIntoVisibles(visibles []*visibleInterval, chunk *filer_pb.FileChunk) (newVisibles []*visibleInterval) {
+	for _, v := range visibles {
+		if v.start < chunk.Offset && chunk.Offset < v.stop {
+			newVisibles = append(newVisibles, newVisibleInterval(
+				v.start,
+				chunk.Offset,
+				v.fileId,
+				v.modifiedTime,
 			))
-			watermarkStart = nextStop
-			logPrintf("parallelIntervals loop intervals =>", intervals)
-
-			// remove processed intervals, possibly multiple
-			var remaining []*visibleInterval
-			for _, interval := range parallelIntervals {
-				if interval.stop != watermarkStart {
-					remaining = append(remaining, interval)
-				}
-			}
-			parallelIntervals = remaining
-			logPrintf("parallelIntervals loop 2", parallelIntervals)
-			logPrintf("parallelIntervals loop 2 intervals", intervals)
 		}
-		parallelIntervals = append(parallelIntervals, newVisibleInterval(
-			chunk.Offset,
-			chunk.Offset+int64(chunk.Size),
-			chunk.FileId,
-			chunk.Mtime,
-		))
-	}
-
-	logPrintf("parallelIntervals loop 3", parallelIntervals)
-	logPrintf("parallelIntervals loop 3 intervals", intervals)
-	for len(parallelIntervals) > 0 {
-		minStopInterval, upToDateInterval = findMinStopInterval(parallelIntervals)
-		intervals = append(intervals, newVisibleInterval(
-			max(watermarkStart, minStopInterval.start),
-			minStopInterval.stop,
-			upToDateInterval.fileId,
-			upToDateInterval.modifiedTime,
-		))
-		watermarkStart = minStopInterval.stop
-
-		// remove processed intervals, possibly multiple
-		var remaining []*visibleInterval
-		for _, interval := range parallelIntervals {
-			if interval.stop != watermarkStart {
-				remaining = append(remaining, interval)
-			}
-		}
-		parallelIntervals = remaining
-	}
-	logPrintf("parallelIntervals loop 4", parallelIntervals)
-	logPrintf("intervals", intervals)
-
-	// merge connected intervals, now the intervals are non-intersecting
-	var lastIntervalIndex int
-	var prevIntervalIndex int
-	for i, interval := range intervals {
-		if i == 0 {
-			prevIntervalIndex = i
-			lastIntervalIndex = i
-			continue
-		}
-		if intervals[i-1].fileId != interval.fileId ||
-			intervals[i-1].stop < intervals[i].start {
-			visibles = append(visibles, newVisibleInterval(
-				intervals[prevIntervalIndex].start,
-				intervals[i-1].stop,
-				intervals[prevIntervalIndex].fileId,
-				intervals[prevIntervalIndex].modifiedTime,
+		chunkStop := chunk.Offset + int64(chunk.Size)
+		if v.start < chunkStop && chunkStop < v.stop {
+			newVisibles = append(newVisibles, newVisibleInterval(
+				chunkStop,
+				v.stop,
+				v.fileId,
+				v.modifiedTime,
 			))
-			prevIntervalIndex = i
 		}
-		lastIntervalIndex = i
-		logPrintf("intervals loop 1 visibles", visibles)
+		if chunkStop < v.start || v.stop <= chunk.Offset {
+			newVisibles = append(newVisibles, v)
+		}
 	}
-
-	visibles = append(visibles, newVisibleInterval(
-		intervals[prevIntervalIndex].start,
-		intervals[lastIntervalIndex].stop,
-		intervals[prevIntervalIndex].fileId,
-		intervals[prevIntervalIndex].modifiedTime,
+	newVisibles = append(newVisibles, newVisibleInterval(
+		chunk.Offset,
+		chunk.Offset+int64(chunk.Size),
+		chunk.FileId,
+		chunk.Mtime,
 	))
-
-	logPrintf("visibles", visibles)
-
 	return
 }
 
-func findMinStopInterval(intervals []*visibleInterval) (minStopInterval, upToDateInterval *visibleInterval) {
-	var latestMtime int64
-	latestIntervalIndex := 0
-	minStop := int64(math.MaxInt64)
-	minIntervalIndex := 0
-	for i, interval := range intervals {
-		if minStop > interval.stop {
-			minIntervalIndex = i
-			minStop = interval.stop
-		}
-		if latestMtime < interval.modifiedTime {
-			latestMtime = interval.modifiedTime
-			latestIntervalIndex = i
-		}
+func nonOverlappingVisibleIntervals(chunks []*filer_pb.FileChunk) (visibles []*visibleInterval) {
+
+	sort.Slice(chunks, func(i, j int) bool {
+		return chunks[i].Mtime < chunks[j].Mtime
+	})
+
+	for _, chunk := range chunks {
+		visibles = mergeIntoVisibles(visibles, chunk)
 	}
-	minStopInterval = intervals[minIntervalIndex]
-	upToDateInterval = intervals[latestIntervalIndex]
+
+	sort.Slice(visibles, func(i, j int) bool {
+		return visibles[i].start < visibles[j].start
+	})
+
+	logPrintf("visibles", visibles)
+
 	return
 }
 
@@ -257,10 +173,3 @@ func min(x, y int64) int64 {
 	}
 	return y
 }
-
-func max(x, y int64) int64 {
-	if x > y {
-		return x
-	}
-	return y
-}