public long computeOnlineDataSizeFastCompositeKeyed(Statistics statistics) {
    return computeOnlineDataSizeGeneric(statistics,
        5 + 4, // list header ; value length stored as vint
        8 // maintenance structure consists of 1 long
    );
  }
ConvertJoinMapJoin is an optimization that replaces a common join
(aka shuffle join) with a map join (aka broadcast or fragment replicate
join when possible. Map joins have restrictions on which joins can be
converted (e.g.: full outer joins cannot be handled as map joins) as well
as memory restrictions (one side of the join has to fit into memory).
ql/src/java/org/apache/hadoop/hive/ql/optimizer/ConvertJoinMapJoin.java