From 919dc0cbc603db274c1351f97848f91edde5f3ab Mon Sep 17 00:00:00 2001
From: Harry John <johrry@amazon.com>
Date: Mon, 16 Sep 2024 23:55:02 -0700
Subject: [PATCH] storage: Update LabelQuerier interface to return sorted label
 values (#14849)
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* Change LabelQuerier.LabelValues() to return sorted values

---------

Signed-off-by: 🌲 Harry 🌊 John 🏔 <johrry@amazon.com>
---
 storage/interface.go |  2 +-
 tsdb/block_test.go   | 28 ++++++++++++++++++++++++++++
 tsdb/head_test.go    | 31 +++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/storage/interface.go b/storage/interface.go
index 2f125e590..a4608e08c 100644
--- a/storage/interface.go
+++ b/storage/interface.go
@@ -157,7 +157,7 @@ type ChunkQuerier interface {
 
 // LabelQuerier provides querying access over labels.
 type LabelQuerier interface {
-	// LabelValues returns all potential values for a label name.
+	// LabelValues returns all potential values for a label name in sorted order.
 	// It is not safe to use the strings beyond the lifetime of the querier.
 	// If matchers are specified the returned result set is reduced
 	// to label values of metrics matching the matchers.
diff --git a/tsdb/block_test.go b/tsdb/block_test.go
index f2569e35b..2273b812a 100644
--- a/tsdb/block_test.go
+++ b/tsdb/block_test.go
@@ -22,6 +22,7 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
+	"slices"
 	"sort"
 	"strconv"
 	"testing"
@@ -310,6 +311,33 @@ func TestLabelValuesWithMatchers(t *testing.T) {
 	}
 }
 
+func TestBlockQuerierReturnsSortedLabelValues(t *testing.T) {
+	tmpdir := t.TempDir()
+	ctx := context.Background()
+
+	var seriesEntries []storage.Series
+	for i := 100; i > 0; i-- {
+		seriesEntries = append(seriesEntries, storage.NewListSeries(labels.FromStrings(
+			"__name__", fmt.Sprintf("value%d", i),
+		), []chunks.Sample{sample{100, 0, nil, nil}}))
+	}
+
+	blockDir := createBlock(t, tmpdir, seriesEntries)
+
+	// Check open err.
+	block, err := OpenBlock(nil, blockDir, nil)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, block.Close()) })
+
+	q, err := newBlockBaseQuerier(block, 0, 100)
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, q.Close()) })
+
+	res, _, err := q.LabelValues(ctx, "__name__", nil)
+	require.NoError(t, err)
+	require.True(t, slices.IsSorted(res))
+}
+
 // TestBlockSize ensures that the block size is calculated correctly.
 func TestBlockSize(t *testing.T) {
 	tmpdir := t.TempDir()
diff --git a/tsdb/head_test.go b/tsdb/head_test.go
index c4e16ae65..ffe3c0494 100644
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@@ -23,6 +23,7 @@ import (
 	"path"
 	"path/filepath"
 	"reflect"
+	"slices"
 	"sort"
 	"strconv"
 	"strings"
@@ -2101,6 +2102,36 @@ func TestHead_LogRollback(t *testing.T) {
 	}
 }
 
+func TestHead_ReturnsSortedLabelValues(t *testing.T) {
+	h, _ := newTestHead(t, 1000, wlog.CompressionNone, false)
+	defer func() {
+		require.NoError(t, h.Close())
+	}()
+
+	h.initTime(0)
+
+	app := h.appender()
+	for i := 100; i > 0; i-- {
+		for j := 0; j < 10; j++ {
+			lset := labels.FromStrings(
+				"__name__", fmt.Sprintf("metric_%d", i),
+				"label", fmt.Sprintf("value_%d", j),
+			)
+			_, err := app.Append(0, lset, 2100, 1)
+			require.NoError(t, err)
+		}
+	}
+
+	q, err := NewBlockQuerier(h, 1500, 2500)
+	require.NoError(t, err)
+
+	res, _, err := q.LabelValues(context.Background(), "__name__", nil)
+	require.NoError(t, err)
+
+	require.True(t, slices.IsSorted(res))
+	require.NoError(t, q.Close())
+}
+
 // TestWalRepair_DecodingError ensures that a repair is run for an error
 // when decoding a record.
 func TestWalRepair_DecodingError(t *testing.T) {