Allow setting custom lookback delta for instant queries (#9946)

* Allow setting custom lookback delta for instant queries

Signed-off-by: Vilius Pranckaitis <vpranckaitis@gmail.com>

promql/engine.go

@@ -128,6 +128,8 @@ type Query interface {
 type QueryOpts struct {
 	// Enables recording per-step statistics if the engine has it enabled as well. Disabled by default.
 	EnablePerStepStats bool
+	// Lookback delta duration for this query.
+	LookbackDelta time.Duration
 }
 
 // query implements the Query interface.
@@ -437,11 +439,17 @@ func (ng *Engine) newQuery(q storage.Queryable, opts *QueryOpts, expr parser.Exp
 		opts = &QueryOpts{}
 	}
 
+	lookbackDelta := opts.LookbackDelta
+	if lookbackDelta <= 0 {
+		lookbackDelta = ng.lookbackDelta
+	}
+
 	es := &parser.EvalStmt{
-		Expr:     PreprocessExpr(expr, start, end),
-		Start:    start,
-		End:      end,
-		Interval: interval,
+		Expr:          PreprocessExpr(expr, start, end),
+		Start:         start,
+		End:           end,
+		Interval:      interval,
+		LookbackDelta: lookbackDelta,
 	}
 	qry := &query{
 		stmt:        es,
@@ -636,7 +644,7 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *parser.Eval
 			ctx:                      ctxInnerEval,
 			maxSamples:               ng.maxSamplesPerQuery,
 			logger:                   ng.logger,
-			lookbackDelta:            ng.lookbackDelta,
+			lookbackDelta:            s.LookbackDelta,
 			samplesStats:             query.sampleStats,
 			noStepSubqueryIntervalFn: ng.noStepSubqueryIntervalFn,
 		}
@@ -688,7 +696,7 @@ func (ng *Engine) execEvalStmt(ctx context.Context, query *query, s *parser.Eval
 		ctx:                      ctxInnerEval,
 		maxSamples:               ng.maxSamplesPerQuery,
 		logger:                   ng.logger,
-		lookbackDelta:            ng.lookbackDelta,
+		lookbackDelta:            s.LookbackDelta,
 		samplesStats:             query.sampleStats,
 		noStepSubqueryIntervalFn: ng.noStepSubqueryIntervalFn,
 	}
@@ -801,7 +809,7 @@ func (ng *Engine) getTimeRangesForSelector(s *parser.EvalStmt, n *parser.VectorS
 	}
 
 	if evalRange == 0 {
-		start = start - durationMilliseconds(ng.lookbackDelta)
+		start = start - durationMilliseconds(s.LookbackDelta)
 	} else {
 		// For all matrix queries we want to ensure that we have (end-start) + range selected
 		// this way we have `range` data before the start time

promql/engine_test.go

@@ -3120,3 +3120,96 @@ func TestRangeQuery(t *testing.T) {
 		})
 	}
 }
+
+func TestQueryLookbackDelta(t *testing.T) {
+	var (
+		load = `load 5m
+metric 0 1 2
+`
+		query           = "metric"
+		lastDatapointTs = time.Unix(600, 0)
+	)
+
+	cases := []struct {
+		name                          string
+		ts                            time.Time
+		engineLookback, queryLookback time.Duration
+		expectSamples                 bool
+	}{
+		{
+			name:          "default lookback delta",
+			ts:            lastDatapointTs.Add(defaultLookbackDelta),
+			expectSamples: true,
+		},
+		{
+			name:          "outside default lookback delta",
+			ts:            lastDatapointTs.Add(defaultLookbackDelta + time.Millisecond),
+			expectSamples: false,
+		},
+		{
+			name:           "custom engine lookback delta",
+			ts:             lastDatapointTs.Add(10 * time.Minute),
+			engineLookback: 10 * time.Minute,
+			expectSamples:  true,
+		},
+		{
+			name:           "outside custom engine lookback delta",
+			ts:             lastDatapointTs.Add(10*time.Minute + time.Millisecond),
+			engineLookback: 10 * time.Minute,
+			expectSamples:  false,
+		},
+		{
+			name:           "custom query lookback delta",
+			ts:             lastDatapointTs.Add(20 * time.Minute),
+			engineLookback: 10 * time.Minute,
+			queryLookback:  20 * time.Minute,
+			expectSamples:  true,
+		},
+		{
+			name:           "outside custom query lookback delta",
+			ts:             lastDatapointTs.Add(20*time.Minute + time.Millisecond),
+			engineLookback: 10 * time.Minute,
+			queryLookback:  20 * time.Minute,
+			expectSamples:  false,
+		},
+		{
+			name:           "negative custom query lookback delta",
+			ts:             lastDatapointTs.Add(20 * time.Minute),
+			engineLookback: -10 * time.Minute,
+			queryLookback:  20 * time.Minute,
+			expectSamples:  true,
+		},
+	}
+
+	for _, c := range cases {
+		c := c
+		t.Run(c.name, func(t *testing.T) {
+			test, err := NewTest(t, load)
+			require.NoError(t, err)
+			defer test.Close()
+
+			err = test.Run()
+			require.NoError(t, err)
+
+			eng := test.QueryEngine()
+			if c.engineLookback != 0 {
+				eng.lookbackDelta = c.engineLookback
+			}
+			opts := &QueryOpts{
+				LookbackDelta: c.queryLookback,
+			}
+			qry, err := eng.NewInstantQuery(test.Queryable(), opts, query, c.ts)
+			require.NoError(t, err)
+
+			res := qry.Exec(test.Context())
+			require.NoError(t, res.Err)
+			vec, ok := res.Value.(Vector)
+			require.True(t, ok)
+			if c.expectSamples {
+				require.NotEmpty(t, vec)
+			} else {
+				require.Empty(t, vec)
+			}
+		})
+	}
+}

promql/parser/ast.go

@@ -68,6 +68,8 @@ type EvalStmt struct {
 	Start, End time.Time
 	// Time between two evaluated instants for the range [Start:End].
 	Interval time.Duration
+	// Lookback delta to use for this evaluation.
+	LookbackDelta time.Duration
 }
 
 func (*EvalStmt) PromQLStmt() {}