* @param partition
* @return
*/
public long estimate(Table catalog_tbl, Column partition_col, int partition) {
TableStatistics table_stats = this.stats.getTableStatistics(catalog_tbl);
ColumnStatistics col_stats = table_stats.getColumnStatistics(partition_col);
String col_key = CatalogKey.createKey(partition_col);
ObjectHistogram<Integer> h = this.cache_table_partition.get(col_key);
if (h == null) {
h = new ObjectHistogram<Integer>();