public String getSingleDbName() {
      if (entities.size() == 1) {
        return entities.keySet().stream().findFirst().get();
      }
      return null;
    }
Request often times only contains tables/partitions of 1 DB only.
@return the single DB name, null if the count of DBs present is not exactly 1.
ql/src/java/org/apache/hadoop/hive/llap/ProactiveEviction.java