Fixes issue with point hitting wrong shard

If a point was written that was earlier than any existing shards
it would be written to the earliest existing shard that had an
end time later than the point's time.

This ensures that when a point is written and there are no shards that
the point will fit into exactly, a new shard group will be created.

CHANGELOG.md

@@ -49,6 +49,7 @@
 - [#7436](https://github.com/influxdata/influxdb/issues/7436): Remove accidentally added string support for the stddev call.
 - [#7161](https://github.com/influxdata/influxdb/issues/7161): Drop measurement causes cache max memory exceeded error.
 - [#7334](https://github.com/influxdata/influxdb/issues/7334): Panic with unread show series iterators during drop database
+- [#7482](https://github.com/influxdata/influxdb/issues/7482): Fix issue where point would be written to wrong shard.
 
 ## v1.0.2 [2016-10-05]
 

coordinator/points_writer.go

@@ -262,7 +262,9 @@ func (l sgList) ShardGroupAt(t time.Time) *meta.ShardGroupInfo {
 	//  - (assuming identical end times) the shard group with the earliest start
 	//    time.
 	idx := sort.Search(len(l), func(i int) bool { return l[i].EndTime.After(t) })
-	if idx == len(l) {
+
+	// We couldn't find a shard group the point falls into.
+	if idx == len(l) || t.Before(l[idx].StartTime) {
 		return nil
 	}
 	return &l[idx]

coordinator/points_writer_internal_test.go

@@ -0,0 +1,46 @@
+package coordinator
+
+import (
+	"testing"
+	"time"
+)
+
+func TestSgList_ShardGroupAt(t *testing.T) {
+	base := time.Date(2016, 10, 19, 0, 0, 0, 0, time.UTC)
+	day := func(n int) time.Time {
+		return base.Add(time.Duration(24*n) * time.Hour)
+	}
+
+	list := sgList{
+		{ID: 1, StartTime: day(0), EndTime: day(1)},
+		{ID: 2, StartTime: day(1), EndTime: day(2)},
+		{ID: 3, StartTime: day(2), EndTime: day(3)},
+		// SG day 3 to day 4 missing...
+		{ID: 4, StartTime: day(4), EndTime: day(5)},
+		{ID: 5, StartTime: day(5), EndTime: day(6)},
+	}
+
+	examples := []struct {
+		T            time.Time
+		ShardGroupID uint64 // 0 will indicate we don't expect a shard group
+	}{
+		{T: base.Add(-time.Minute), ShardGroupID: 0}, // Before any SG
+		{T: day(0), ShardGroupID: 1},
+		{T: day(0).Add(time.Minute), ShardGroupID: 1},
+		{T: day(1), ShardGroupID: 2},
+		{T: day(3).Add(time.Minute), ShardGroupID: 0}, // No matching SG
+		{T: day(5).Add(time.Hour), ShardGroupID: 5},
+	}
+
+	for i, example := range examples {
+		sg := list.ShardGroupAt(example.T)
+		var id uint64
+		if sg != nil {
+			id = sg.ID
+		}
+
+		if got, exp := id, example.ShardGroupID; got != exp {
+			t.Errorf("[Example %d] got %v, expected %v", i+1, got, exp)
+		}
+	}
+}