If you set DataPageSize to All for a group level, and that group level is the only group level on the page or the highest group level on the page, all the records will be displayed when you open the page in Page view or in Microsoft Internet Explorer. If a page contains many records, it might take longer to load the page.
Note If a group level doesn't have a record navigation section or a record navigation control, you must set DataPageSize to All in order to see all the records for that group level.