Thread

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

Hannu Krosing <hannuk@google.com> — 2025-07-07T23:39:59Z

On Mon, Jul 7, 2025 at 11:38 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>

> > Also added a flag to select number of direct values to show
>
> Hmm ... I agree with having a way to control the length of that output,
> but I don't think that specifying a count is the most useful way to
> do it.  Particularly with a default of only 10, it seems way too
> likely to cut off important information.
>
> What do you think of instead specifying the limit as the maximum
> running-percentage to print, with a default of say 99.99%?  That
> gives me results like

I agree that percentage covered is a much better metric indeed.
And I am equally ok with a default of either 99.9% or 99.99%.

I briefly thought of it but decided a simple count is simpler to
explain, especially for some potential corner cases of % .
But as pg_test_timing is not part of the server we really do not need
to worry about rare edge cases.


> Observed timing durations up to 99.9900%:
>       ns   % of total  running %      count
>       15       4.5452     4.5452    8313178
>       16      58.3785    62.9237  106773354
>       17      33.6840    96.6078   61607584
>       18       3.1151    99.7229    5697480
>       19       0.2638    99.9867     482570
>       20       0.0093    99.9960      17054
>
> In the attached I also made it print the largest observed
> duration, which seems like it might be useful information.

Yes, a useful piece of information indeed.

> As previously threatened, I also added a test case to
> improve the code coverage.

Thanks!