What is more, if the square root calculation is affecting your benchmarks, I suspect you are benchmarking the wrong thing.
I run another test that has two pgbench-clients in same time, one is select-only-query and another is executing 'SELECT * pg_stat_statement' query in every one second. I used v6 patch in this test.
The issue of concern is not the performance of pg_stat_statements, AUIU. The issue is whether this patch affects performance generally, i.e. is there a significant cost in collecting these extra stats. To test this you would compare two general pgbench runs, one with the patch applied and one without.
I showed first test result which is compared with without pg_stat_statements and without patch last day. They ran in same server and same benchmark settings(clients and scale factor) as today's result. When you merge and see the results, you can confirm not to affect of performance in my patch.
