Re: What is a typical precision of gettimeofday()?

BTW, returning to the original topic of this thread:

The new exact-delays table from pg_test_timing is really quite
informative.  For example, on my M4 Macbook:

Observed timing durations up to 99.9900%:
      ns   % of total  running %      count
       0      62.2124    62.2124  118127987
      41      12.5826    74.7951   23891661
      42      25.1653    99.9604   47783489
      83       0.0194    99.9797      36744
      84       0.0096    99.9893      18193
     125       0.0020    99.9913       3784
...
   31042       0.0000   100.0000          1

The fact that the clock tick is about 40ns is extremely 
obvious in this presentation.

Even more interesting is what I got from an ancient PPC Macbook
(mamba's host, running NetBSD):

Testing timing overhead for 3 seconds.
Per loop time including overhead: 731.26 ns
...
Observed timing durations up to 99.9900%:
      ns   % of total  running %      count
     705      39.9162    39.9162    1637570
     706      17.6040    57.5203     722208
     759      18.6797    76.2000     766337
     760      23.7851    99.9851     975787
     813       0.0002    99.9853          9
     814       0.0004    99.9857         17
     868       0.0001    99.9858          4
     922       0.0001    99.9859          3
...
  564950       0.0000   100.0000          1

I had previously reported that that machine had microsecond
timing precision, but this shows that the real problem is that
it takes most of a microsecond to go 'round the timing loop.
It seems clear that the system clock ticks about every 50ns,
even on this decades-old hardware.

            regards, tom lane