Remove inmem lastModified time

This was added for preventing concurrent writes and deletes to the
same series.  This is not handled by the bitsets for both tsi and
inmme.  The time.Now() calls shows up in profiles and is not needed.

tsdb/index/inmem/inmem.go

@@ -752,11 +752,6 @@ func (i *Index) DropSeriesGlobal(key []byte, ts int64) error {
 		return nil
 	}
 
-	// Series was recently created, we can't drop it.
-	if series.LastModified() >= ts {
-		return nil
-	}
-
 	// Update the tombstone sketch.
 	i.seriesTSSketch.Add([]byte(k))
 
@@ -766,7 +761,7 @@ func (i *Index) DropSeriesGlobal(key []byte, ts int64) error {
 	// Remove the measurement's reference.
 	series.Measurement.DropSeries(series)
 	// Mark the series as deleted.
-	series.Delete(ts)
+	series.Delete()
 
 	// If the measurement no longer has any series, remove it as well.
 	if !series.Measurement.HasSeries() {

tsdb/index/inmem/meta.go

@@ -6,8 +6,6 @@ import (
 	"regexp"
 	"sort"
 	"sync"
-	"sync/atomic"
-	"time"
 
 	"github.com/influxdata/influxdb/models"
 	"github.com/influxdata/influxdb/pkg/bytesutil"
@@ -1052,12 +1050,8 @@ func (a measurements) Union(other measurements) measurements {
 
 // series belong to a Measurement and represent unique time series in a database.
 type series struct {
-	mu sync.RWMutex
-	// lastModified tracks the last time the series was created.  If the series
-	// already exists and a request to create is received (a no-op), lastModified
-	// is increased to track that it is still in use.
-	lastModified int64
-	deleted      bool
+	mu      sync.RWMutex
+	deleted bool
 
 	// immutable
 	ID          uint64
@@ -1069,24 +1063,17 @@ type series struct {
 // newSeries returns an initialized series struct
 func newSeries(id uint64, m *measurement, key string, tags models.Tags) *series {
 	return &series{
-		ID:           id,
-		Measurement:  m,
-		Key:          key,
-		Tags:         tags,
-		lastModified: time.Now().UTC().UnixNano(),
+		ID:          id,
+		Measurement: m,
+		Key:         key,
+		Tags:        tags,
 	}
 }
 
-func (s *series) LastModified() int64 {
-	return atomic.LoadInt64(&s.lastModified)
-}
-
 // Delete marks this series as deleted.  A deleted series should not be returned for queries.
-func (s *series) Delete(ts int64) {
+func (s *series) Delete() {
 	s.mu.Lock()
-	if s.LastModified() < ts {
-		s.deleted = true
-	}
+	s.deleted = true
 	s.mu.Unlock()
 }