Hello
pg_stat_statements is a great tool to track performance issue in live 
databases, especially when adding interfaces like PoWA on top of it.
But so far, tools like PoWA can not track the min_time, max_time, mean_time 
and sum_var_time of queries : these statistics are cumulated over time, 
fetching points in time would be of little to no use, especially when looking 
at the impact of a DDL change.
This patch thus introduces a simple pg_stat_statements_reset_computed_values 
function that reset the computed statistics, leaving all other information 
alive, thus allowing the aforementioned scenario.
Regards
 Pierre Ducroquet