set hive.auto.convert.join = true;
explain
 SELECT sum(hash(a.key, a.value, b.key, b.value))
 FROM 
  (
  SELECT src1.key as key, count(src1.value) AS value FROM src src1 group by src1.key
  ) a
 FULL OUTER JOIN 
 (
  SELECT src2.key as key, count(distinct(src2.value)) AS value 
  FROM src1 src2 group by src2.key
 ) b 
 ON (a.key = b.key);
 

 SELECT sum(hash(a.key, a.value, b.key, b.value))
 FROM 
  (
  SELECT src1.key as key, count(src1.value) AS value FROM src src1 group by src1.key
  ) a
 FULL OUTER JOIN 
 (
  SELECT src2.key as key, count(distinct(src2.value)) AS value 
  FROM src1 src2 group by src2.key
 ) b 
 ON (a.key = b.key);