app/vmselect/promql: properly return an empty result from limit_offset() if offset exceeds the number of inner time series

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3312

app/vmselect/promql/exec_test.go

@@ -2291,6 +2291,16 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{r}
 		f(q, resultExpected)
 	})
+	t.Run(`limit_offset(too-big-offset)`, func(t *testing.T) {
+		t.Parallel()
+		q := `limit_offset(1, 10, sort_by_label((
+			label_set(time()*1, "foo", "y"),
+			label_set(time()*2, "foo", "a"),
+			label_set(time()*3, "foo", "x"),
+		), "foo"))`
+		resultExpected := []netstorage.Result{}
+		f(q, resultExpected)
+	})
 	t.Run(`limit_offset NaN`, func(t *testing.T) {
 		t.Parallel()
 		// q returns 3 time series, where foo=3 contains only NaN values

app/vmselect/promql/transform.go

@@ -1943,6 +1943,8 @@ func transformLimitOffset(tfa *transformFuncArg) ([]*timeseries, error) {
 	rvs := removeEmptySeries(args[2])
 	if len(rvs) >= offset {
 		rvs = rvs[offset:]
+	} else {
+		rvs = nil
 	}
 	if len(rvs) > limit {
 		rvs = rvs[:limit]

docs/CHANGELOG.md

@@ -24,6 +24,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 * FEATURE: [vmui](https://docs.victoriametrics.com/#vmui): add the ability to hide results of a particular query by clicking the `eye` icon. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/3359).
 * FEATURE: [vmalert](https://docs.victoriametrics.com/vmalert.html): add default alert list for vmalert's metrics. See [alerts-vmalert.yml](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/deployment/docker/alerts-vmalert.yml).
 
+* BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly return an empty result from [limit_offset](https://docs.victoriametrics.com/MetricsQL.html#limit_offset) if the `offset` arg exceeds the number of inner time series. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3312).
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): properly display the requested graph on the requested time range when navigating from Prometheus URL in Grafana.
 * BUGFIX: reduce CPU usage spikes and memory usage spikes under high data ingestion rate introduced in [v1.83.0](https://docs.victoriametrics.com/CHANGELOG.html#v1830). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3343).