fix: double buffer was invalid when put entry which size larger than max size (#31549)

relate: https://github.com/milvus-io/milvus/issues/31548

---------

Signed-off-by: aoiasd <zhicheng.yue@zilliz.com>

internal/querynodev2/delegator/deletebuffer/delete_buffer.go

@@ -64,8 +64,7 @@ func (c *doubleCacheBuffer[T]) Put(entry T) {
 
 	err := c.head.Put(entry)
 	if errors.Is(err, errBufferFull) {
-		c.evict(entry.Timestamp())
-		c.head.Put(entry)
+		c.evict(entry.Timestamp(), entry)
 	}
 }
 
@@ -84,9 +83,14 @@ func (c *doubleCacheBuffer[T]) ListAfter(ts uint64) []T {
 }
 
 // evict sets head as tail and evicts tail.
-func (c *doubleCacheBuffer[T]) evict(newTs uint64) {
+func (c *doubleCacheBuffer[T]) evict(newTs uint64, entry T) {
 	c.tail = c.head
-	c.head = newDoubleCacheItem[T](newTs, c.maxSize/2)
+	c.head = &doubleCacheItem[T]{
+		headTs:  newTs,
+		maxSize: c.maxSize / 2,
+		size:    entry.Size(),
+		data:    []T{entry},
+	}
 	c.ts = c.tail.headTs
 }
 

internal/querynodev2/delegator/deletebuffer/delete_buffer_test.go

@@ -78,6 +78,58 @@ func (s *DoubleCacheBufferSuite) TestCache() {
 	s.Equal(1, len(buffer.ListAfter(12)))
 }
 
+func (s *DoubleCacheBufferSuite) TestPut() {
+	buffer := NewDoubleCacheDeleteBuffer[*Item](10, 1)
+	buffer.Put(&Item{
+		Ts: 11,
+		Data: []BufferItem{
+			{
+				PartitionID: 200,
+				DeleteData: storage.DeleteData{
+					Pks:      []storage.PrimaryKey{storage.NewVarCharPrimaryKey("test1")},
+					Tss:      []uint64{11},
+					RowCount: 1,
+				},
+			},
+		},
+	})
+
+	buffer.Put(&Item{
+		Ts: 12,
+		Data: []BufferItem{
+			{
+				PartitionID: 200,
+				DeleteData: storage.DeleteData{
+					Pks:      []storage.PrimaryKey{storage.NewVarCharPrimaryKey("test2")},
+					Tss:      []uint64{12},
+					RowCount: 1,
+				},
+			},
+		},
+	})
+
+	s.Equal(2, len(buffer.ListAfter(11)))
+	s.Equal(1, len(buffer.ListAfter(12)))
+
+	buffer.Put(&Item{
+		Ts: 13,
+		Data: []BufferItem{
+			{
+				PartitionID: 200,
+				DeleteData: storage.DeleteData{
+					Pks:      []storage.PrimaryKey{storage.NewVarCharPrimaryKey("test3")},
+					Tss:      []uint64{13},
+					RowCount: 1,
+				},
+			},
+		},
+	})
+
+	s.Equal(2, len(buffer.ListAfter(11)))
+	s.Equal(2, len(buffer.ListAfter(12)))
+	s.Equal(1, len(buffer.ListAfter(13)))
+}
+
 func TestDoubleCacheDeleteBuffer(t *testing.T) {
 	suite.Run(t, new(DoubleCacheBufferSuite))
 }