Ensure orphaned series removed from inmem index

This commit ensures that any orphaned series (series that are to be
removed and no longer are referenced anywhere in the database) are
removed from the `inmem` index when a shard is dropped.

tsdb/store.go

@@ -678,9 +678,6 @@ func (s *Store) DeleteShard(shardID uint64) error {
 	ss := index.SeriesIDSet()
 
 	db := sh.Database()
-	if err := sh.Close(); err != nil {
-		return err
-	}
 
 	// Determine if the shard contained any series that are not present in any
 	// other shards in the database.
@@ -701,10 +698,42 @@ func (s *Store) DeleteShard(shardID uint64) error {
 	if ss.Cardinality() > 0 {
 		sfile := s.seriesFile(db)
 		if sfile != nil {
+			// If the inmem index is in use, then the series being removed from the
+			// series file will also need to be removed from the index.
+			if index.Type() == InmemIndexName {
+				var keyBuf []byte // Series key buffer.
+				var name []byte
+				var tagsBuf models.Tags // Buffer for tags container.
+				var err error
+
+				ss.ForEach(func(id uint64) {
+					skey := sfile.SeriesKey(id) // Series File series key
+					if skey == nil {
+						return
+					}
+
+					name, tagsBuf = ParseSeriesKeyInto(skey, tagsBuf)
+					keyBuf = models.AppendMakeKey(keyBuf, name, tagsBuf)
+					if err = index.DropSeriesGlobal(keyBuf); err != nil {
+						return
+					}
+				})
+
+				if err != nil {
+					return err
+				}
+			}
+
 			ss.ForEach(func(id uint64) {
 				sfile.DeleteSeriesID(id)
 			})
 		}
+
+	}
+
+	// Close the shard.
+	if err := sh.Close(); err != nil {
+		return err
 	}
 
 	// Remove the on-disk shard data.