Re: Timing overhead and Linux clock sources

On Sat, Aug 25, 2012 at 10:48 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> On Mon, Aug 20, 2012 at 03:11:51PM -0400, Robert Haas wrote:
>> On Thu, Aug 16, 2012 at 10:28 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> > FYI, I am planning to go ahead and package this tool in /contrib for PG
>> > 9.3.
>>
>> Isn't this exactly what we already did, in 9.2, in the form of
>> contrib/pg_test_timing?
>
> Sorry, not sure how I missed that commit. Anyway, I am attaching a
> patch for 9.3 that I think improves the output of the tool, plus adds
> some C comments.
>
> The new output has the lowest duration times first:
>
> Testing timing overhead for 3 seconds.
> Per loop time including overhead: 41.31 nsec
> Histogram of timing durations:
> < usec % of total count
> 1 95.87135 69627856
> 2 4.12759 2997719
> 4 0.00086 628
> 8 0.00018 133
> 16 0.00001 5
> 32 0.00000 1
>
> This should make the output clearer to eyeball for problems --- a good
> timing has a high percentage on the first line, rather than on the last
> line.

I guess I'm not sure the output format is an improvement. I wouldn't
care much one way or the other if we had made this change at the time
in AS92, but I'm not sure it's really worth breaking compatibility for
a format that may or may not be any better. The person who wrote the
original code presumably preferred it way it already is.

--
Robert Haas
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