Merge remote-tracking branch 'origin/master'

db/db_impl.h

@@ -120,7 +120,7 @@ class DBImpl : public DB {
   };
 
   Status get_slot_num(const ReadOptions& options, const Slice& key,
-                      size_t *slot_num);
+                      size_t *slot_num) override;
 
   Iterator* NewInternalIterator(const ReadOptions&,
                                 SequenceNumber* latest_snapshot,