diff --git a/other/java/client/src/main/java/seaweedfs/client/ReadChunks.java b/other/java/client/src/main/java/seaweedfs/client/ReadChunks.java
new file mode 100644
index 000000000..2eba4f808
--- /dev/null
+++ b/other/java/client/src/main/java/seaweedfs/client/ReadChunks.java
@@ -0,0 +1,109 @@
+package seaweedfs.client;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+public class ReadChunks {
+
+    public static List<SeaweedRead.VisibleInterval> readResolvedChunks(List<FilerProto.FileChunk> chunkList) throws IOException {
+        List<Point> points = new ArrayList<>(chunkList.size() * 2);
+        for (FilerProto.FileChunk chunk : chunkList) {
+            points.add(new Point(chunk.getOffset(), chunk, true));
+            points.add(new Point(chunk.getOffset() + chunk.getSize(), chunk, false));
+        }
+        Collections.sort(points, new Comparator<Point>() {
+            @Override
+            public int compare(Point a, Point b) {
+                int x = (int) (a.x - b.x);
+                if (a.x != b.x) {
+                    return (int) (a.x - b.x);
+                }
+                if (a.ts != b.ts) {
+                    return (int) (a.ts - b.ts);
+                }
+                if (!a.isStart) {
+                    return -1;
+                }
+                return 1;
+            }
+        });
+
+        long prevX = 0;
+        List<SeaweedRead.VisibleInterval> visibles = new ArrayList<>();
+        ArrayList<Point> queue = new ArrayList<>();
+        for (Point point : points) {
+            if (point.isStart) {
+                if (queue.size() > 0) {
+                    int lastIndex = queue.size() - 1;
+                    Point lastPoint = queue.get(lastIndex);
+                    if (point.x != prevX && lastPoint.ts < point.ts) {
+                        addToVisibles(visibles, prevX, lastPoint, point);
+                        prevX = point.x;
+                    }
+                }
+                // insert into queue
+                for (int i = queue.size(); i >= 0; i--) {
+                    if (i == 0 || queue.get(i - 1).ts <= point.ts) {
+                        if (i == queue.size()) {
+                            prevX = point.x;
+                        }
+                        queue.add(i, point);
+                        break;
+                    }
+                }
+            } else {
+                int lastIndex = queue.size() - 1;
+                int index = lastIndex;
+                Point startPoint = null;
+                for (; index >= 0; index--) {
+                    startPoint = queue.get(index);
+                    if (startPoint.ts == point.ts) {
+                        queue.remove(index);
+                        break;
+                    }
+                }
+                if (index == lastIndex && startPoint != null) {
+                    addToVisibles(visibles, prevX, startPoint, point);
+                    prevX = point.x;
+                }
+            }
+        }
+
+        return visibles;
+
+    }
+
+    private static void addToVisibles(List<SeaweedRead.VisibleInterval> visibles, long prevX, Point startPoint, Point point) {
+        if (prevX < point.x) {
+            FilerProto.FileChunk chunk = startPoint.chunk;
+            visibles.add(new SeaweedRead.VisibleInterval(
+                    prevX,
+                    point.x,
+                    chunk.getFileId(),
+                    chunk.getMtime(),
+                    prevX - chunk.getOffset(),
+                    chunk.getOffset() == prevX && chunk.getSize() == prevX - startPoint.x,
+                    chunk.getCipherKey().toByteArray(),
+                    chunk.getIsCompressed()
+            ));
+        }
+    }
+
+    static class Point {
+        long x;
+        long ts;
+        FilerProto.FileChunk chunk;
+        boolean isStart;
+
+        public Point(long x, FilerProto.FileChunk chunk, boolean isStart) {
+            this.x = x;
+            this.ts = chunk.getMtime();
+            this.chunk = chunk;
+            this.isStart = isStart;
+        }
+    }
+
+}
diff --git a/other/java/client/src/main/java/seaweedfs/client/SeaweedRead.java b/other/java/client/src/main/java/seaweedfs/client/SeaweedRead.java
index 011462a17..41033befb 100644
--- a/other/java/client/src/main/java/seaweedfs/client/SeaweedRead.java
+++ b/other/java/client/src/main/java/seaweedfs/client/SeaweedRead.java
@@ -226,96 +226,8 @@ public class SeaweedRead {
 
         chunkList = FileChunkManifest.resolveChunkManifest(filerClient, chunkList);
 
-        FilerProto.FileChunk[] chunks = chunkList.toArray(new FilerProto.FileChunk[0]);
-        Arrays.sort(chunks, new Comparator<FilerProto.FileChunk>() {
-            @Override
-            public int compare(FilerProto.FileChunk a, FilerProto.FileChunk b) {
-                // if just a.getMtime() - b.getMtime(), it will overflow!
-                if (a.getMtime() < b.getMtime()) {
-                    return -1;
-                } else if (a.getMtime() > b.getMtime()) {
-                    return 1;
-                }
-                return 0;
-            }
-        });
+        return ReadChunks.readResolvedChunks(chunkList);
 
-        List<VisibleInterval> visibles = new ArrayList<>();
-        for (FilerProto.FileChunk chunk : chunks) {
-            List<VisibleInterval> newVisibles = new ArrayList<>();
-            visibles = mergeIntoVisibles(visibles, newVisibles, chunk);
-        }
-
-        return visibles;
-    }
-
-    private static List<VisibleInterval> mergeIntoVisibles(List<VisibleInterval> visibles,
-                                                           List<VisibleInterval> newVisibles,
-                                                           FilerProto.FileChunk chunk) {
-        VisibleInterval newV = new VisibleInterval(
-                chunk.getOffset(),
-                chunk.getOffset() + chunk.getSize(),
-                chunk.getFileId(),
-                chunk.getMtime(),
-                0,
-                true,
-                chunk.getCipherKey().toByteArray(),
-                chunk.getIsCompressed()
-        );
-
-        // easy cases to speed up
-        if (visibles.size() == 0) {
-            visibles.add(newV);
-            return visibles;
-        }
-        if (visibles.get(visibles.size() - 1).stop <= chunk.getOffset()) {
-            visibles.add(newV);
-            return visibles;
-        }
-
-        for (VisibleInterval v : visibles) {
-            if (v.start < chunk.getOffset() && chunk.getOffset() < v.stop) {
-                newVisibles.add(new VisibleInterval(
-                        v.start,
-                        chunk.getOffset(),
-                        v.fileId,
-                        v.modifiedTime,
-                        v.chunkOffset,
-                        false,
-                        v.cipherKey,
-                        v.isCompressed
-                ));
-            }
-            long chunkStop = chunk.getOffset() + chunk.getSize();
-            if (v.start < chunkStop && chunkStop < v.stop) {
-                newVisibles.add(new VisibleInterval(
-                        chunkStop,
-                        v.stop,
-                        v.fileId,
-                        v.modifiedTime,
-                        v.chunkOffset + (chunkStop - v.start),
-                        false,
-                        v.cipherKey,
-                        v.isCompressed
-                ));
-            }
-            if (chunkStop <= v.start || v.stop <= chunk.getOffset()) {
-                newVisibles.add(v);
-            }
-        }
-        newVisibles.add(newV);
-
-        // keep everything sorted
-        for (int i = newVisibles.size() - 1; i >= 0; i--) {
-            if (i > 0 && newV.start < newVisibles.get(i - 1).start) {
-                newVisibles.set(i, newVisibles.get(i - 1));
-            } else {
-                newVisibles.set(i, newV);
-                break;
-            }
-        }
-
-        return newVisibles;
     }
 
     public static String parseVolumeId(String fileId) {
diff --git a/other/java/client/src/test/java/seaweedfs/client/SeaweedReadTest.java b/other/java/client/src/test/java/seaweedfs/client/SeaweedReadTest.java
index 44b833c90..6ad9edb2c 100644
--- a/other/java/client/src/test/java/seaweedfs/client/SeaweedReadTest.java
+++ b/other/java/client/src/test/java/seaweedfs/client/SeaweedReadTest.java
@@ -6,6 +6,7 @@ import org.junit.Test;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Random;
 
 public class SeaweedReadTest {
 
@@ -13,17 +14,17 @@ public class SeaweedReadTest {
     public void testNonOverlappingVisibleIntervals() throws IOException {
         List<FilerProto.FileChunk> chunks = new ArrayList<>();
         chunks.add(FilerProto.FileChunk.newBuilder()
-            .setFileId("aaa")
-            .setOffset(0)
-            .setSize(100)
-            .setMtime(1000)
-            .build());
+                .setFileId("aaa")
+                .setOffset(0)
+                .setSize(100)
+                .setMtime(1000)
+                .build());
         chunks.add(FilerProto.FileChunk.newBuilder()
-            .setFileId("bbb")
-            .setOffset(100)
-            .setSize(133)
-            .setMtime(2000)
-            .build());
+                .setFileId("bbb")
+                .setOffset(100)
+                .setSize(133)
+                .setMtime(2000)
+                .build());
 
         List<SeaweedRead.VisibleInterval> visibleIntervals = SeaweedRead.nonOverlappingVisibleIntervals(null, chunks);
         for (SeaweedRead.VisibleInterval visibleInterval : visibleIntervals) {
@@ -61,4 +62,106 @@ public class SeaweedReadTest {
 
     }
 
+
+    @Test
+    public void testReadResolvedChunks() throws IOException {
+        List<FilerProto.FileChunk> chunks = new ArrayList<>();
+        chunks.add(FilerProto.FileChunk.newBuilder()
+                .setFileId("a")
+                .setOffset(0)
+                .setSize(100)
+                .setMtime(1)
+                .build());
+        chunks.add(FilerProto.FileChunk.newBuilder()
+                .setFileId("b")
+                .setOffset(50)
+                .setSize(100)
+                .setMtime(2)
+                .build());
+        chunks.add(FilerProto.FileChunk.newBuilder()
+                .setFileId("c")
+                .setOffset(200)
+                .setSize(50)
+                .setMtime(3)
+                .build());
+        chunks.add(FilerProto.FileChunk.newBuilder()
+                .setFileId("d")
+                .setOffset(250)
+                .setSize(50)
+                .setMtime(4)
+                .build());
+        chunks.add(FilerProto.FileChunk.newBuilder()
+                .setFileId("e")
+                .setOffset(175)
+                .setSize(100)
+                .setMtime(5)
+                .build());
+
+        List<SeaweedRead.VisibleInterval> visibleIntervals = ReadChunks.readResolvedChunks(chunks);
+        for (SeaweedRead.VisibleInterval visibleInterval : visibleIntervals) {
+            System.out.println("visible:" + visibleInterval);
+        }
+
+        Assert.assertEquals(4, visibleIntervals.size());
+
+        SeaweedRead.VisibleInterval visibleInterval = visibleIntervals.get(0);
+        Assert.assertEquals(visibleInterval.start, 0);
+        Assert.assertEquals(visibleInterval.stop, 50);
+        Assert.assertEquals(visibleInterval.modifiedTime, 1);
+        Assert.assertEquals(visibleInterval.fileId, "a");
+
+        visibleInterval = visibleIntervals.get(1);
+        Assert.assertEquals(visibleInterval.start, 50);
+        Assert.assertEquals(visibleInterval.stop, 150);
+        Assert.assertEquals(visibleInterval.modifiedTime, 2);
+        Assert.assertEquals(visibleInterval.fileId, "b");
+
+        visibleInterval = visibleIntervals.get(2);
+        Assert.assertEquals(visibleInterval.start, 175);
+        Assert.assertEquals(visibleInterval.stop, 275);
+        Assert.assertEquals(visibleInterval.modifiedTime, 5);
+        Assert.assertEquals(visibleInterval.fileId, "e");
+
+        visibleInterval = visibleIntervals.get(3);
+        Assert.assertEquals(visibleInterval.start, 275);
+        Assert.assertEquals(visibleInterval.stop, 300);
+        Assert.assertEquals(visibleInterval.modifiedTime, 4);
+        Assert.assertEquals(visibleInterval.fileId, "d");
+
+    }
+
+
+    @Test
+    public void testRandomizedReadResolvedChunks() throws IOException {
+        Random random = new Random();
+        int limit = 1024*1024;
+        long[] array = new long[limit];
+        List<FilerProto.FileChunk> chunks = new ArrayList<>();
+        for (long ts=0;ts<1024;ts++){
+            int x = random.nextInt(limit);
+            int y = random.nextInt(limit);
+            int size = Math.min(Math.abs(x-y), 1024);
+            chunks.add(randomWrite(array, Math.min(x,y), size, ts));
+        }
+
+        List<SeaweedRead.VisibleInterval> visibleIntervals = ReadChunks.readResolvedChunks(chunks);
+        for (SeaweedRead.VisibleInterval visibleInterval : visibleIntervals) {
+            System.out.println("visible:" + visibleInterval);
+            for (int i = (int) visibleInterval.start; i<visibleInterval.stop; i++) {
+                Assert.assertEquals(array[i], visibleInterval.modifiedTime);
+            }
+        }
+
+    }
+    private FilerProto.FileChunk randomWrite(long[] array, int start, int size, long ts) {
+        for (int i=start;i<start+size;i++) {
+            array[i] = ts;
+        }
+        return FilerProto.FileChunk.newBuilder()
+                .setFileId("")
+                .setOffset(start)
+                .setSize(size)
+                .setMtime(ts)
+                .build();
+    }
 }
diff --git a/weed/filer/filechunks.go b/weed/filer/filechunks.go
index 0dc03f6e2..be18d45ac 100644
--- a/weed/filer/filechunks.go
+++ b/weed/filer/filechunks.go
@@ -225,6 +225,12 @@ func NonOverlappingVisibleIntervals(lookupFileIdFn wdclient.LookupFileIdFunction
 
 	chunks, _, err = ResolveChunkManifest(lookupFileIdFn, chunks, startOffset, stopOffset)
 
+	visibles2 := readResolvedChunks(chunks)
+
+	if true {
+		return visibles2, err
+	}
+
 	sort.Slice(chunks, func(i, j int) bool {
 		if chunks[i].Mtime == chunks[j].Mtime {
 			filer_pb.EnsureFid(chunks[i])
@@ -246,9 +252,26 @@ func NonOverlappingVisibleIntervals(lookupFileIdFn wdclient.LookupFileIdFunction
 
 	}
 
+	if len(visibles) != len(visibles2) {
+		fmt.Printf("different visibles size %d : %d\n", len(visibles), len(visibles2))
+	} else {
+		for i := 0; i < len(visibles); i++ {
+			checkDifference(visibles[i], visibles2[i])
+		}
+	}
+
 	return
 }
 
+func checkDifference(x, y VisibleInterval) {
+	if x.start != y.start ||
+		x.stop != y.stop ||
+		x.fileId != y.fileId ||
+		x.modifiedTime != y.modifiedTime {
+		fmt.Printf("different visible %+v : %+v\n", x, y)
+	}
+}
+
 // find non-overlapping visible intervals
 // visible interval map to one file chunk
 
diff --git a/weed/filer/filechunks_read.go b/weed/filer/filechunks_read.go
new file mode 100644
index 000000000..b39f6a35c
--- /dev/null
+++ b/weed/filer/filechunks_read.go
@@ -0,0 +1,119 @@
+package filer
+
+import (
+	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
+	"sort"
+)
+
+func readResolvedChunks(chunks []*filer_pb.FileChunk) (visibles []VisibleInterval) {
+
+	var points []*Point
+	for _, chunk := range chunks {
+		points = append(points, &Point{
+			x:       chunk.Offset,
+			ts:      chunk.Mtime,
+			chunk:   chunk,
+			isStart: true,
+		})
+		points = append(points, &Point{
+			x:       chunk.Offset + int64(chunk.Size),
+			ts:      chunk.Mtime,
+			chunk:   chunk,
+			isStart: false,
+		})
+	}
+	sort.Slice(points, func(i, j int) bool {
+		if points[i].x != points[j].x {
+			return points[i].x < points[j].x
+		}
+		if points[i].ts != points[j].ts {
+			return points[i].ts < points[j].ts
+		}
+		if !points[i].isStart {
+			return true
+		}
+		return false
+	})
+
+	var prevX int64
+	var queue []*Point
+	for _, point := range points {
+		if point.isStart {
+			if len(queue) > 0 {
+				lastIndex := len(queue) -1
+				lastPoint := queue[lastIndex]
+				if point.x != prevX && lastPoint.ts < point.ts {
+					visibles = addToVisibles(visibles, prevX, lastPoint, point)
+					prevX = point.x
+				}
+			}
+			// insert into queue
+			for i := len(queue); i >= 0; i-- {
+				if i == 0 || queue[i-1].ts <= point.ts {
+					if i == len(queue) {
+						prevX = point.x
+					}
+					queue = addToQueue(queue, i, point)
+					break
+				}
+			}
+		} else {
+			lastIndex := len(queue) - 1
+			index := lastIndex
+			var startPoint *Point
+			for ; index >= 0; index-- {
+				startPoint = queue[index]
+				if startPoint.ts == point.ts {
+					queue = removeFromQueue(queue, index)
+					break
+				}
+			}
+			if index == lastIndex && startPoint != nil {
+				visibles = addToVisibles(visibles, prevX, startPoint, point)
+				prevX = point.x
+			}
+		}
+	}
+
+	return
+}
+
+func removeFromQueue(queue []*Point, index int) []*Point {
+	for i := index; i < len(queue)-1; i++ {
+		queue[i] = queue[i+1]
+	}
+	queue = queue[:len(queue)-1]
+	return queue
+}
+
+func addToQueue(queue []*Point, index int, point *Point) []*Point {
+	queue = append(queue, point)
+	for i := len(queue) - 1; i > index; i-- {
+		queue[i], queue[i-1] = queue[i-1], queue[i]
+	}
+	return queue
+}
+
+func addToVisibles(visibles []VisibleInterval, prevX int64, startPoint *Point, point *Point) []VisibleInterval {
+	if prevX < point.x {
+		chunk := startPoint.chunk
+		visibles = append(visibles, VisibleInterval{
+			start:        prevX,
+			stop:         point.x,
+			fileId:       chunk.FileId,
+			modifiedTime: chunk.Mtime,
+			chunkOffset:  prevX - chunk.Offset,
+			chunkSize:    chunk.Size,
+			cipherKey:    chunk.CipherKey,
+			isGzipped:    chunk.IsCompressed,
+		})
+	}
+	return visibles
+}
+
+type Point struct {
+	x       int64
+	ts      int64
+	chunk   *filer_pb.FileChunk
+	isStart bool
+}
diff --git a/weed/filer/filechunks_read_test.go b/weed/filer/filechunks_read_test.go
new file mode 100644
index 000000000..1920f5185
--- /dev/null
+++ b/weed/filer/filechunks_read_test.go
@@ -0,0 +1,119 @@
+package filer
+
+import (
+	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
+	"math/rand"
+	"testing"
+)
+
+func TestReadResolvedChunks(t *testing.T) {
+
+	chunks := []*filer_pb.FileChunk{
+		{
+			FileId: "a",
+			Offset: 0,
+			Size:   100,
+			Mtime:  1,
+		},
+		{
+			FileId: "b",
+			Offset: 50,
+			Size:   100,
+			Mtime:  2,
+		},
+		{
+			FileId: "c",
+			Offset: 200,
+			Size:   50,
+			Mtime:  3,
+		},
+		{
+			FileId: "d",
+			Offset: 250,
+			Size:   50,
+			Mtime:  4,
+		},
+		{
+			FileId: "e",
+			Offset: 175,
+			Size:   100,
+			Mtime:  5,
+		},
+	}
+
+	visibles := readResolvedChunks(chunks)
+
+	for _, visible := range visibles {
+		fmt.Printf("[%d,%d) %s %d\n", visible.start, visible.stop, visible.fileId, visible.modifiedTime)
+	}
+
+}
+
+func TestRandomizedReadResolvedChunks(t *testing.T) {
+
+	var limit int64 = 1024*1024
+	array := make([]int64, limit)
+	var chunks []*filer_pb.FileChunk
+	for ts := int64(0); ts < 1024; ts++ {
+		x := rand.Int63n(limit)
+		y := rand.Int63n(limit)
+		size := x - y
+		if size < 0 {
+			size = -size
+		}
+		if size > 1024 {
+			size = 1024
+		}
+		start := x
+		if start > y {
+			start = y
+		}
+		chunks = append(chunks, randomWrite(array, start, size, ts))
+	}
+
+	visibles := readResolvedChunks(chunks)
+
+	for _, visible := range visibles {
+		for i := visible.start; i<visible.stop;i++{
+			if array[i] != visible.modifiedTime {
+				t.Errorf("position %d expected ts %d actual ts %d", i, array[i], visible.modifiedTime)
+			}
+		}
+	}
+
+	// fmt.Printf("visibles %d", len(visibles))
+
+}
+
+func randomWrite(array []int64, start int64, size int64, ts int64) *filer_pb.FileChunk {
+	for i := start; i < start+size; i++ {
+		array[i] = ts
+	}
+	// fmt.Printf("write [%d,%d) %d\n", start, start+size, ts)
+	return &filer_pb.FileChunk{
+		FileId: "",
+		Offset: start,
+		Size:   uint64(size),
+		Mtime:  ts,
+	}
+}
+
+func TestSequentialReadResolvedChunks(t *testing.T) {
+
+	var chunkSize int64 = 1024*1024*2
+	var chunks []*filer_pb.FileChunk
+	for ts := int64(0); ts < 13; ts++ {
+		chunks = append(chunks, &filer_pb.FileChunk{
+			FileId: "",
+			Offset: chunkSize*ts,
+			Size:   uint64(chunkSize),
+			Mtime:  1,
+		})
+	}
+
+	visibles := readResolvedChunks(chunks)
+
+	fmt.Printf("visibles %d", len(visibles))
+
+}