If you have large reports where the SQL query executed can take 10+ seconds then currently reportbuilder will execute this query twice as it has to count the number of total rows in the report for the paging bar:

https://github.com/moodle/moodle/blob/master/reportbuilder/classes/table/base_report_table.php#L177

This results in the loading of the report to take 20+ seconds as it executes the slow query twice.

We could halve the loading time by counting the number of total rows from the query which fetches the data