[time-nuts] Thunderbolt Data Plotting

Hal Murray hmurray at megapathdsl.net
Fri Jul 11 14:41:39 EDT 2008

> Well - I have lots and lots of raw numbers, and no really good way of
> plottinng it. I'm hardly a linux guru, but would gnuplot be a suitable
> tool for graphing data like the snipper below? 

It's what I use.

gnuplot has zillions of options.  You will probably have to read (or at least 
skim) the whoie manual to get a feel for how to do things.  Once you know 
what you are looking for, the online help works pretty well.

An important question is how to organize your raw data.  I copied the setup 
from ntpd's "day" mode.  It uses 1 file per day with filenames like 
loopstats.20080628.  The first two columns of the file are the modified 
julian day and seconds within the current day.  For example:
  54658 64083.850 -0.000002000 118.700 0.000016330 0.009421 9
  54658 64149.858 -0.000022000 118.700 0.000016849 0.008813 9
  54658 64215.865 -0.000040000 118.699 0.000016956 0.008251 9
  54658 64280.873 -0.000049000 118.698 0.000016187 0.007726 9
  54658 64346.881 -0.000064000 118.697 0.000015979 0.007236 9
You can also link loopstats (no date) to the latest one so tail loopstats 
gets you the latest/current one without bothering to figure out what the date 

I generally set things up so I can easily plot the last two files.  That 
gives somewhere between 24 and 48 hours so I always have some context if an 
interesting quirk happens at the start of a day.

I have a handful of scripts that grab log files from several machines and 
setup links to the latest two.  For example, foo-loop goes to 
foo/loopstats.20080711 and foo-loop-1 goes to foo/loopstats.20080710  Then 
the gnuplot include files just refer to foo-loop and foo-oop-1  When making 
graphs, I ignore the first column and add a 24 hour offset on one file to the 
plot command.

That generally works OK for looking at events with a time scale of hours.  I 
haven't tried looking for long term (days, months) trends.  If/when I want to 
do that, I'll probably do some pre-processing and make a new file with one 
line per day or hour.

These are my opinions, not necessarily my employer's.  I hate spam.

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