Avoid infinite loop on duplicate NaN values. (prometheus#4275)

Fixes prometheus#4254 NaNs don't equal themselves, so a duplicate NaN would always hit the break statement and never get popped. We should not be returning multiple data point for the same timestamp, so don't compare values at all. Signed-off-by: Brian Brazil <[email protected]>
LW945 · Jun 18, 2018 · 78efdc6 · 78efdc6
1 parent 8cd59da
commit 78efdc6
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Showing 2 changed files with 18 additions and 3 deletions.
diff --git a/storage/fanout.go b/storage/fanout.go
@@ -450,10 +450,10 @@ func (c *mergeIterator) Next() bool {
 		return false
 	}
 
-	currt, currv := c.At()
+	currt, _ := c.At()
 	for len(c.h) > 0 {
-		nextt, nextv := c.h[0].At()
-		if nextt != currt || nextv != currv {
+		nextt, _ := c.h[0].At()
+		if nextt != currt {
 			break
 		}
 

diff --git a/storage/fanout_test.go b/storage/fanout_test.go
@@ -15,6 +15,7 @@ package storage
 
 import (
 	"fmt"
+	"math"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -97,6 +98,16 @@ func TestMergeSeriesSet(t *testing.T) {
 				newMockSeries(labels.FromStrings("foo", "bar"), []sample{{0, 0}, {1, 1}, {2, 2}, {3, 3}}),
 			),
 		},
+		{
+			input: []SeriesSet{newMockSeriesSet(
+				newMockSeries(labels.FromStrings("foo", "bar"), []sample{{0, math.NaN()}}),
+			), newMockSeriesSet(
+				newMockSeries(labels.FromStrings("foo", "bar"), []sample{{0, math.NaN()}}),
+			)},
+			expected: newMockSeriesSet(
+				newMockSeries(labels.FromStrings("foo", "bar"), []sample{{0, math.NaN()}}),
+			),
+		},
 	} {
 		merged := NewMergeSeriesSet(tc.input)
 		for merged.Next() {
@@ -197,6 +208,10 @@ func drainSamples(iter SeriesIterator) []sample {
 	result := []sample{}
 	for iter.Next() {
 		t, v := iter.At()
+		// NaNs can't be compared normally, so substitute for another value.
+		if math.IsNaN(v) {
+			v = -42
+		}
 		result = append(result, sample{t, v})
 	}
 	return result