When the GROUP BY clause of the SQL is specified for grouping, grouping is performed after sorting. Rapid grouping is accomplished by combining hashing with grouping. The rapid grouping facility reduces the time required for grouping as the number of groups to be grouped gets smaller and as the number of rows gets larger.

In HiRDB/Parallel Server, you must also consider the grouping processing method, because how the floatable servers are used affects performance. For details about grouping processing methods, see 4.5.5 Grouping processing methods (HiRDB/Parallel Server only).