fix disk blk_read_bytes being negative due to diffps

Author: chengjoey

internal/tools/monitor/core/metric/query/es-tsql/influxql/ckFunctions.go

@@ -210,6 +210,11 @@ var CkAggFunctions = map[string]*SQlAggFuncDefine{
 							}
 							seconds := float64(ctx.interval*int64(ctx.targetTimeUnit)) / float64(tsql.Second)
 							nextValue := nextV[id].(float64)
+							// diffps return value should not be negative
+							// erda issue: https://erda.cloud/erda/dop/projects/387/issues/all?id=581160&iterationID=12783&tab=BUG&type=BUG
+							if nextValue < currentV {
+								return 0, true
+							}
 							return (nextValue - currentV) / seconds, true
 						}
 					}

internal/tools/monitor/core/metric/query/es-tsql/influxql/ckFunctions_test.go

@@ -283,7 +283,7 @@ func TestAggregationHandlerFunction(t *testing.T) {
 			nextRow: map[string]interface{}{
 				"0e4b5b1082a11703": float64(111),
 			},
-			want: (111.0 - 222.0) / 60.0,
+			want: 0,
 		},
 
 		{