On 2/13/26 3:42 PM, Hannu Krosing wrote:
> I haven't looked at the code here yet, but when using plain rdtsc on
> modern CPUs one sees much more overhead from just the fact that the
> code is there than from calling the rdtsc instruction, and the
> overhead can vary by orders of magnitude based on how complex the work
> is that is timed.
>
> I discovered this when I timed the (then-)new dead tid lookups in the
> Vacuum in Pg 17 and saw significantly larger overhead per lookup when
> the lookups themselves were slower, i.e. a case where the lookups were
> done in random order (inded was on created on a column filled with
> random())
>
> So while just a tight loop of N million rtdsc calls will give you the
> lower limit, it is likely not very representative of actual overhead.
Isn't the same issue still there if you call clock_gettime() but that it
is just less noticeable due to the high cost of clock_gettime()?
Andreas
