From aa31cc85f5817d78ae41eaa2a70fdc987c71ef37 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Mon, 21 Nov 2022 16:46:02 +0200
Subject: [PATCH] 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 | 10 ++++++++++
 app/vmselect/promql/transform.go |  2 ++
 docs/CHANGELOG.md                |  1 +
 3 files changed, 13 insertions(+)

diff --git a/app/vmselect/promql/exec_test.go b/app/vmselect/promql/exec_test.go
index 8ab1ae8df..6c85d4cfb 100644
--- a/app/vmselect/promql/exec_test.go
+++ b/app/vmselect/promql/exec_test.go
@@ -2290,6 +2290,16 @@ 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
diff --git a/app/vmselect/promql/transform.go b/app/vmselect/promql/transform.go
index ea87225aa..cec3aac5a 100644
--- a/app/vmselect/promql/transform.go
+++ b/app/vmselect/promql/transform.go
@@ -1878,6 +1878,8 @@ 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]
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 4eac7246f..51464a961 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -15,6 +15,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 
 ## v1.79.x long-time support release (LTS)
 
+* 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: [vmagent](https://docs.victoriametrics.com/vmagent.html): properly discover GCE zones when `filter` option is set at [gce_sd_configs](https://docs.victoriametrics.com/sd_configs.html#gce_sd_configs). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3202).
 
 ## [v1.79.5](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.79.5)