An order by clause specifies that a select
statement returns a result set with the rows being sorted by the values of the key
columns.
DA server requires source and target table rows to be sorted before they can be compared.
For very large tables, this sorting may have a large negative impact on the Adaptive
Server temporary database space. To reduce the impact of processing
order
by clause in the databases, use the external sort option, which:
- Omits the order by clause and receives unsorted rows from the
database.
- Sorts rows as they are written to flat files on your system.
- Reads simultaneously from all flat files and returns the sorted rows for
comparison.
You can control and configure the external sort option by tuning the associated
configuration parameters for best possible results.
To use this option, set external_sort to true.