fix: optimise write window check

coordinator/points_writer.go

@@ -121,10 +121,37 @@ func (s *ShardMapping) MapPoint(shardInfo *meta.ShardInfo, p models.Point) {
 	s.Shards[shardInfo.ID] = shardInfo
 }
 
-func withinWriteWindow(rp *meta.RetentionPolicyInfo, p models.Point) bool {
-	if (rp != nil) &&
-		(((rp.FutureWriteLimit > 0) && p.Time().After(time.Now().Add(rp.FutureWriteLimit))) ||
-			((rp.PastWriteLimit > 0) && p.Time().Before(time.Now().Add(-rp.PastWriteLimit)))) {
+type WriteWindow struct {
+	before      time.Time
+	checkBefore bool
+	after       time.Time
+	checkAfter  bool
+}
+
+func NewWriteWindow(rp *meta.RetentionPolicyInfo) *WriteWindow {
+	w := &WriteWindow{checkAfter: false, checkBefore: false}
+
+	if rp == nil {
+		// Used in tests
+		return w
+	}
+	now := time.Now()
+	if rp.FutureWriteLimit > 0 {
+		w.after = now.Add(rp.FutureWriteLimit)
+		w.checkAfter = true
+	}
+	if rp.PastWriteLimit > 0 {
+		w.before = now.Add(-rp.PastWriteLimit)
+		w.checkBefore = true
+	}
+	return w
+}
+
+func (w *WriteWindow) WithinWindow(t time.Time) bool {
+	if w.checkBefore && t.Before(w.before) {
+		return false
+	}
+	if w.checkAfter && t.After(w.after) {
 		return false
 	}
 	return true
@@ -197,11 +224,12 @@ func (w *PointsWriter) MapShards(wp *WritePointsRequest) (*ShardMapping, error)
 		min = time.Now().Add(-rp.Duration)
 	}
 
+	ww := NewWriteWindow(rp)
 	for _, p := range wp.Points {
 		// Either the point is outside the scope of the RP, we already have
 		// a suitable shard group for the point, or it is outside the write window
 		// for the RP, and we don't want to unnecessarily create a shard for it
-		if p.Time().Before(min) || list.Covers(p.Time()) || !withinWriteWindow(rp, p) {
+		if p.Time().Before(min) || list.Covers(p.Time()) || !ww.WithinWindow(p.Time()) {
 			continue
 		}
 
@@ -221,7 +249,7 @@ func (w *PointsWriter) MapShards(wp *WritePointsRequest) (*ShardMapping, error)
 	mapping := NewShardMapping(len(wp.Points))
 	for _, p := range wp.Points {
 		sg := list.ShardGroupAt(p.Time())
-		if sg == nil || !withinWriteWindow(rp, p) {
+		if sg == nil || !ww.WithinWindow(p.Time()) {
 			// We didn't create a shard group because the point was outside the
 			// scope of the RP, or the point is outside the write window for the RP.
 			mapping.Dropped = append(mapping.Dropped, p)