Hello, hackers. Today I was doing some aggregates over pg_stat_statements in order to find types of queries consuming most of the CPU. Aggregates were made on two pg_state_statement snapshots within 30 sec delay.
The sum(total_time) had the biggest value for a very frequent query with about 10ms execution. I was thinking it is the biggest CPU consumer. But after reducing the frequency of queries a lot I was unable to see any significant difference in server CPU usage... So, looks like clock_gettime is not so accurate to measure real CPU usage for some OLTP workloads. I suppose it is caused by the wall time vs CPU time difference (IO, thread switch, etc). But what do you think about adding cpu_time (by calling getrusage) to pg_stat_statements? Seems it could be very useful for CPU profiling. I am probably able to prepare the patch, but it is always better to get some feedback on the idea first :) Best regards, Michail.
