On 6/11/24 13:13, Robert Haas wrote:
On Tue, Jun 11, 2024 at 5:49 AM Bertrand Drouvot
<bertranddrouvot...@gmail.com> wrote:
As we can see the actual wait time is 30ms less than the intended wait time with
this simple test. So I still think we should go with 1) actual wait time and 2)
report the number of waits (as mentioned in [1]). Does that make sense to you?
I like the idea of reporting the actual wait time better, provided
that we verify that doing so isn't too expensive. I think it probably
isn't, because in a long-running VACUUM there is likely to be disk
I/O, so the CPU overhead of a few extra gettimeofday() calls should be
fairly low by comparison. I wonder if there's a noticeable hit when
everything is in-memory. I guess probably not, because with any sort
of normal configuration, we shouldn't be delaying after every block we
process, so the cost of those gettimeofday() calls should still be
getting spread across quite a bit of real work.
Does it even require a call to gettimeofday()? The code in vacuum
calculates an msec value and calls pg_usleep(msec * 1000). I don't think
it is necessary to measure how long that nap was.
Regards, Jan
