diff --git a/internal/datanode/buffer.go b/internal/datanode/buffer.go
index f1b0a4e160..8d88a9afa1 100644
--- a/internal/datanode/buffer.go
+++ b/internal/datanode/buffer.go
@@ -296,6 +296,7 @@ func (ddb *DelDataBuf) mergeDelDataBuf(buf *DelDataBuf) {
 
 	tr := TimeRange{timestampMax: buf.TimestampTo, timestampMin: buf.TimestampFrom}
 	ddb.updateTimeRange(tr)
+	ddb.updateStartAndEndPosition(buf.startPos, buf.endPos)
 
 	ddb.delData.Pks = append(ddb.delData.Pks, buf.delData.Pks...)
 	ddb.delData.Tss = append(ddb.delData.Tss, buf.delData.Tss...)
diff --git a/internal/datanode/buffer_test.go b/internal/datanode/buffer_test.go
index 7971e30470..102277f114 100644
--- a/internal/datanode/buffer_test.go
+++ b/internal/datanode/buffer_test.go
@@ -27,6 +27,7 @@ import (
 
 	"github.com/milvus-io/milvus-proto/go-api/commonpb"
 	"github.com/milvus-io/milvus-proto/go-api/schemapb"
+	"github.com/milvus-io/milvus/internal/proto/internalpb"
 )
 
 func genTestCollectionSchema(dim int64) *schemapb.CollectionSchema {
@@ -162,10 +163,12 @@ func Test_CompactSegBuff(t *testing.T) {
 	//2. set up deleteDataBuf for seg1 and seg2
 	delDataBuf1 := newDelDataBuf()
 	delDataBuf1.EntriesNum++
+	delDataBuf1.updateStartAndEndPosition(nil, &internalpb.MsgPosition{Timestamp: 50})
 	delBufferManager.Store(segID1, delDataBuf1)
 	heap.Push(delBufferManager.delBufHeap, delDataBuf1.item)
 	delDataBuf2 := newDelDataBuf()
 	delDataBuf2.EntriesNum++
+	delDataBuf2.updateStartAndEndPosition(nil, &internalpb.MsgPosition{Timestamp: 50})
 	delBufferManager.Store(segID2, delDataBuf2)
 	heap.Push(delBufferManager.delBufHeap, delDataBuf2.item)
 
@@ -180,4 +183,16 @@ func Test_CompactSegBuff(t *testing.T) {
 	assert.False(t, seg1Exist)
 	assert.False(t, seg2Exist)
 	assert.Equal(t, int64(2), delBufferManager.GetEntriesNum(compactedToSegID))
+
+	//5. test roll and evict (https://github.com/milvus-io/milvus/issues/20501)
+	delBufferManager.channel.rollDeleteBuffer(compactedToSegID)
+	_, segCompactedToExist := delBufferManager.Load(compactedToSegID)
+	assert.False(t, segCompactedToExist)
+	delBufferManager.channel.evictHistoryDeleteBuffer(compactedToSegID, &internalpb.MsgPosition{
+		Timestamp: 100,
+	})
+	cp := delBufferManager.channel.getChannelCheckpoint(&internalpb.MsgPosition{
+		Timestamp: 200,
+	})
+	assert.Equal(t, Timestamp(200), cp.Timestamp) // evict all buffer, use ttPos as cp
 }