Re: Timing overhead and Linux clock sources

On Mon, Aug 27, 2012 at 04:42:34PM -0400, Robert Haas wrote:
> On Mon, Aug 27, 2012 at 1:18 PM, Bruce Momjian <bruce@momjian.us> wrote:
> > He wrote it that way to allow for simpler C code --- he could just start
> > from 31 and keeping skipping entries until he hit a non-zero.
> >
> > My format makes it easy to see which line should have the majority of
> > the entries, e.g. first line should be > 90%.  I doubt there are enough
> > people running this cross-version that consistency in output makes any
> > difference between major PG versions.
> 
> I don't see why it's better for the first line to have a big number
> than the last line.  What difference does it make?

When you are looking at that output, the <1 usec is where you want to
see most of the percentage, and it trails off after that.

Here is an example from the current output format:
Histogram of timing durations:   < usec:      count   percent       16:          3  0.00007%        8:        563
0.01357%       4:       3241  0.07810%        2:    2990371 72.05956%        1:    1155682 27.84870%
 

That first line is pretty meaningless.  You have to look at the last
line, see that only 27% of <1, then look up to see that 72% is 1<2,
which isn't good.  My format shows:
< usec   % of total      count     1     27.84870    1155682     2     72.05956    2990371     4      0.07810
3241    8      0.01357        563    16      0.00007          3
 

First line, 27%, that's a problem, look down for more details.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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