Merge pull request #602 from andyli029:feature_fix_lack_tag_comment

PiperOrigin-RevId: 420781095

db/memtable.cc

@@ -78,6 +78,7 @@ void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
   // Format of an entry is concatenation of:
   //  key_size     : varint32 of internal_key.size()
   //  key bytes    : char[internal_key.size()]
+  //  tag          : uint64((sequence << 8) | type)
   //  value_size   : varint32 of value.size()
   //  value bytes  : char[value.size()]
   size_t key_size = key.size();