public static Statistics collectStatistics(HiveConf conf, PrunedPartitionList partList,
      Table table, List<ColumnInfo> schema, List<String> neededColumns, ColumnStatsList colStatsCache,
      List<String> referencedColumns, boolean needColStats)
      throws HiveException {
    return collectStatistics(conf, partList, table, schema, neededColumns, colStatsCache,
        referencedColumns, needColStats, false);
  }
Returns number of rows if it exists. Otherwise it estimates number of rows
based on estimated data size for both partition and non-partitioned table
RelOptHiveTable's getRowCount uses this.
ql/src/java/org/apache/hadoop/hive/ql/stats/StatsUtils.java