On Mon, Aug 8, 2016 at 7:03 PM, Bruce Momjian <bruce@momjian.us> wrote: > It seems asking users to run pg_test_timing before deploying to check > the overhead would be sufficient.
I'am not sure. Time measurement for waits is slightly more complicated than a time measurement for explain analyze: a good workload plus using gettimeofday in a straightforward manner can cause huge overhead.
What makes you think so? Both my thoughts and observations are opposite: it's way easier to get huge overhead from EXPLAIN ANALYZE than from measuring wait events. Current wait events are quite huge events itself related to syscalls, context switches and so on. In contrast EXPLAIN ANALYZE calls gettimeofday for very cheap operations like transfer tuple from one executor node to another.
Thats why a proper testing is important - if we can see a significant performance drop if we have for example large shared_buffers with the same concurrency, that shows gettimeofday is too expensive to use. Am I correct, that we do not have such accurate tests now?
Do you think that large shared buffers is a kind a stress test for wait events monitoring? If so, why?