fix: prevent silently dropped writes with overlapping shards (#21946)

Co-authored-by: Geoffrey Wossum <gwossum@influxdata.com>

CHANGELOG.md

@@ -67,6 +67,7 @@ This release adds an embedded SQLite database for storing metadata required by t
 1. [21839](https://github.com/influxdata/influxdb/pull/21839): Fix display and parsing of `influxd upgrade` CLI prompts in PowerShell.
 1. [21850](https://github.com/influxdata/influxdb/pull/21850): Systemd unit should block on startup until http endpoint is ready
 1. [21925](https://github.com/influxdata/influxdb/pull/21925): Upgrade to golang-jwt 3.2.1.
+1. [21946](https://github.com/influxdata/influxdb/pull/21946): Prevent silently dropped writes when there are overlapping shards.
 
 ## v2.0.7 [2021-06-04]
 

cmd/influxd/launcher/storage_test.go

@@ -327,3 +327,45 @@ func TestLauncher_UpdateRetentionPolicy(t *testing.T) {
 		})
 	}
 }
+
+func TestLauncher_OverlappingShards(t *testing.T) {
+	l := launcher.RunAndSetupNewLauncherOrFail(ctx, t)
+	defer l.ShutdownOrFail(t, ctx)
+
+	bkt := influxdb.Bucket{Name: "test", ShardGroupDuration: time.Hour, OrgID: l.Org.ID}
+	require.NoError(t, l.BucketService(t).CreateBucket(ctx, &bkt))
+
+	req := l.MustNewHTTPRequest("POST", fmt.Sprintf("/api/v2/write?org=%s&bucket=%s", l.Org.ID, bkt.ID),
+		"m,s=0 n=0 1626416520000000000\nm,s=0 n=1 1626420120000000000\n")
+	resp, err := nethttp.DefaultClient.Do(req)
+	require.NoError(t, err)
+	require.NoError(t, resp.Body.Close())
+
+	newDur := humanize.Day
+	_, err = l.BucketService(t).UpdateBucket(ctx, bkt.ID, influxdb.BucketUpdate{ShardGroupDuration: &newDur})
+	require.NoError(t, err)
+
+	req = l.MustNewHTTPRequest("POST", fmt.Sprintf("/api/v2/write?org=%s&bucket=%s", l.Org.ID, bkt.ID),
+		// NOTE: The 3rd point's timestamp is chronologically earlier than the other two points, but it
+		// must come after the others in the request to trigger the overlapping-shard bug. If it comes
+		// first in the request, the bug is avoided because:
+		//   1. The point-writer sees there is no shard for the earlier point, and creates a new 24h shard-group
+		//   2. The new 24 group covers the timestamps of the remaining 2 points, so the writer doesn't bother looking
+		//      for existing shards that also cover the timestamp
+		//   3. With only 1 shard mapped to the 3 points, there is no overlap to trigger the bug
+		"m,s=0 n=0 1626416520000000000\nm,s=0 n=1 1626420120000000000\nm,s=1 n=1 1626412920000000000\n")
+	resp, err = nethttp.DefaultClient.Do(req)
+	require.NoError(t, err)
+	require.NoError(t, resp.Body.Close())
+
+	query := `from(bucket:"test") |> range(start:2000-01-01T00:00:00Z,stop:2050-01-01T00:00:00Z)` +
+		` |> drop(columns:["_start","_stop"])`
+	exp := `,result,table,_time,_value,_field,_measurement,s` + "\r\n" +
+		`,_result,0,2021-07-16T06:22:00Z,0,n,m,0` + "\r\n" +
+		`,_result,0,2021-07-16T07:22:00Z,1,n,m,0` + "\r\n" +
+		`,_result,1,2021-07-16T05:22:00Z,1,n,m,1` + "\r\n\r\n"
+
+	buf, err := http.SimpleQuery(l.URL(), query, l.Org.Name, l.Auth.Token)
+	require.NoError(t, err)
+	require.Equal(t, exp, string(buf))
+}

v1/coordinator/points_writer.go

@@ -197,7 +197,7 @@ func (w *PointsWriter) MapShards(wp *WritePointsRequest) (*ShardMapping, error)
 	}
 
 	// Holds all the shard groups and shards that are required for writes.
-	list := make(sgList, 0, 8)
+	list := sgList{items: make(meta.ShardGroupInfos, 0, 8)}
 	min := time.Unix(0, models.MinNanoTime)
 	if rp.Duration > 0 {
 		min = time.Now().Add(-rp.Duration)
@@ -220,7 +220,7 @@ func (w *PointsWriter) MapShards(wp *WritePointsRequest) (*ShardMapping, error)
 		if sg == nil {
 			return nil, errors.New("nil shard group")
 		}
-		list = list.Append(*sg)
+		list.Add(*sg)
 	}
 
 	mapping := NewShardMapping(len(wp.Points))
@@ -242,10 +242,21 @@ func (w *PointsWriter) MapShards(wp *WritePointsRequest) (*ShardMapping, error)
 
 // sgList is a wrapper around a meta.ShardGroupInfos where we can also check
 // if a given time is covered by any of the shard groups in the list.
-type sgList meta.ShardGroupInfos
+type sgList struct {
+	items meta.ShardGroupInfos
+
+	// needsSort indicates if items has been modified without a sort operation.
+	needsSort bool
+
+	// earliest is the last begin time of any item in items.
+	earliest time.Time
+
+	// latest is the greatest end time of any item in items.
+	latest time.Time
+}
 
 func (l sgList) Covers(t time.Time) bool {
-	if len(l) == 0 {
+	if len(l.items) == 0 {
 		return false
 	}
 	return l.ShardGroupAt(t) != nil
@@ -261,20 +272,61 @@ func (l sgList) Covers(t time.Time) bool {
 //  - a shard group with the earliest end time;
 //  - (assuming identical end times) the shard group with the earliest start time.
 func (l sgList) ShardGroupAt(t time.Time) *meta.ShardGroupInfo {
-	idx := sort.Search(len(l), func(i int) bool { return l[i].EndTime.After(t) })
-
-	// We couldn't find a shard group the point falls into.
-	if idx == len(l) || t.Before(l[idx].StartTime) {
+	if l.items.Len() == 0 {
 		return nil
 	}
-	return &l[idx]
+
+	// find the earliest shardgroup that could contain this point using binary search.
+	if l.needsSort {
+		sort.Sort(l.items)
+		l.needsSort = false
+	}
+	idx := sort.Search(l.items.Len(), func(i int) bool { return l.items[i].EndTime.After(t) })
+
+	// Check if sort.Search actually found the proper shard. It feels like we should also
+	// be checking l.items[idx].EndTime, but sort.Search was looking at that field for us.
+	if idx == l.items.Len() || t.Before(l.items[idx].StartTime) {
+		// This could mean we are looking for a time not in the list, or we have
+		// overlaping shards. Overlapping shards do not work with binary searches
+		// on 1d arrays. You have to use an interval tree, but that's a lot of
+		// work for what is hopefully a rare event. Instead, we'll check if t
+		// should be in l, and perform a linear search if it is. This way we'll
+		// do the correct thing, it may just take a little longer. If we don't
+		// do this, then we may non-silently drop writes we should have accepted.
+
+		if t.Before(l.earliest) || t.After(l.latest) {
+			// t is not in range, we can avoid going through the linear search.
+			return nil
+		}
+
+		// Oh no, we've probably got overlapping shards. Perform a linear search.
+		for idx = 0; idx < l.items.Len(); idx++ {
+			if l.items[idx].Contains(t) {
+				// Found it!
+				break
+			}
+		}
+		if idx == l.items.Len() {
+			// We did not find a shard which contained t. This is very strange.
+			return nil
+		}
+	}
+
+	return &l.items[idx]
 }
 
-// Append appends a shard group to the list, and returns a sorted list.
-func (l sgList) Append(sgi meta.ShardGroupInfo) sgList {
-	next := append(l, sgi)
-	sort.Sort(meta.ShardGroupInfos(next))
-	return next
+// Add appends a shard group to the list, updating the earliest/latest times of the list if needed.
+func (l *sgList) Add(sgi meta.ShardGroupInfo) {
+	l.items = append(l.items, sgi)
+	l.needsSort = true
+
+	// Update our earliest and latest times for l.items
+	if l.earliest.IsZero() || l.earliest.After(sgi.StartTime) {
+		l.earliest = sgi.StartTime
+	}
+	if l.latest.IsZero() || l.latest.Before(sgi.EndTime) {
+		l.latest = sgi.EndTime
+	}
 }
 
 // WritePoints writes the data to the underlying storage. consistencyLevel and user are only used for clustered scenarios

v1/coordinator/points_writer_internal_test.go

@@ -3,6 +3,9 @@ package coordinator
 import (
 	"testing"
 	"time"
+
+	"github.com/influxdata/influxdb/v2/v1/services/meta"
+	"github.com/stretchr/testify/require"
 )
 
 func TestSgList_ShardGroupAt(t *testing.T) {
@@ -11,7 +14,7 @@ func TestSgList_ShardGroupAt(t *testing.T) {
 		return base.Add(time.Duration(24*n) * time.Hour)
 	}
 
-	list := sgList{
+	items := meta.ShardGroupInfos{
 		{ID: 1, StartTime: day(0), EndTime: day(1)},
 		{ID: 2, StartTime: day(1), EndTime: day(2)},
 		{ID: 3, StartTime: day(2), EndTime: day(3)},
@@ -19,6 +22,10 @@ func TestSgList_ShardGroupAt(t *testing.T) {
 		{ID: 4, StartTime: day(4), EndTime: day(5)},
 		{ID: 5, StartTime: day(5), EndTime: day(6)},
 	}
+	var list sgList
+	for _, i := range items {
+		list.Add(i)
+	}
 
 	examples := []struct {
 		T            time.Time
@@ -44,3 +51,47 @@ func TestSgList_ShardGroupAt(t *testing.T) {
 		}
 	}
 }
+
+func TestSgList_ShardGroupAtOverlapping(t *testing.T) {
+	base := time.Date(2016, 10, 19, 0, 0, 0, 0, time.UTC)
+	hour := func(n int) time.Time {
+		return base.Add(time.Duration(n) * time.Hour)
+	}
+	day := func(n int) time.Time {
+		return base.Add(time.Duration(24*n) * time.Hour)
+	}
+
+	items := meta.ShardGroupInfos{
+		{ID: 1, StartTime: hour(5), EndTime: hour(6)},
+		{ID: 2, StartTime: hour(6), EndTime: hour(7)},
+		// Day-long shard overlaps with the two hour-long shards.
+		{ID: 3, StartTime: base, EndTime: day(1)},
+	}
+	var list sgList
+	for _, i := range items {
+		list.Add(i)
+	}
+
+	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: base, ShardGroupID: 3},
+		{T: hour(5), ShardGroupID: 1},
+		{T: hour(7).Add(-time.Minute), ShardGroupID: 2},
+		{T: hour(8), ShardGroupID: 3},
+		{T: day(2), ShardGroupID: 0}, // No matching SG
+	}
+
+	for _, example := range examples {
+		t.Run(example.T.String(), func(t *testing.T) {
+			sg := list.ShardGroupAt(example.T)
+			var id uint64
+			if sg != nil {
+				id = sg.ID
+			}
+			require.Equal(t, example.ShardGroupID, id)
+		})
+	}
+}