Stablize the sorting of meta.ShardGroupInfos

services/meta/data.go

@@ -1012,9 +1012,25 @@ type ShardGroupInfo struct {
 // on the StartTime field.
 type ShardGroupInfos []ShardGroupInfo
 
-func (a ShardGroupInfos) Len() int           { return len(a) }
-func (a ShardGroupInfos) Less(i, j int) bool { return a[i].StartTime.Before(a[j].StartTime) }
-func (a ShardGroupInfos) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a ShardGroupInfos) Len() int      { return len(a) }
+func (a ShardGroupInfos) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a ShardGroupInfos) Less(i, j int) bool {
+	iEnd := a[i].EndTime
+	if a[i].Truncated() {
+		iEnd = a[i].TruncatedAt
+	}
+
+	jEnd := a[j].EndTime
+	if a[j].Truncated() {
+		jEnd = a[j].TruncatedAt
+	}
+
+	if iEnd.Equal(jEnd) {
+		return a[i].StartTime.Before(a[j].StartTime)
+	}
+
+	return iEnd.Before(jEnd)
+}
 
 // Contains return true if the shard group contains data for the timestamp.
 func (sgi *ShardGroupInfo) Contains(timestamp time.Time) bool {

services/meta/data_test.go

@@ -2,6 +2,8 @@ package meta
 
 import (
 	"reflect"
+	"sort"
+	"time"
 
 	"testing"
 )
@@ -29,3 +31,26 @@ func TestnewShardOwner(t *testing.T) {
 		t.Errorf("got owner frequencies %v, expected %v", got, exp)
 	}
 }
+
+func TestShardGroupSort(t *testing.T) {
+	sg1 := ShardGroupInfo{
+		ID:          1,
+		StartTime:   time.Unix(1000, 0),
+		EndTime:     time.Unix(1100, 0),
+		TruncatedAt: time.Unix(1050, 0),
+	}
+
+	sg2 := ShardGroupInfo{
+		ID:        2,
+		StartTime: time.Unix(1000, 0),
+		EndTime:   time.Unix(1100, 0),
+	}
+
+	sgs := ShardGroupInfos{sg2, sg1}
+
+	sort.Sort(sgs)
+
+	if sgs[len(sgs)-1].ID != 2 {
+		t.Fatal("unstable sort for ShardGroupInfos")
+	}
+}