[rrd-users] [rrd] Can't I turn off data smoothing for GAUGE?

[Philip Peake]

 Then for a huge class of problems, actually, IMHO, most real world
problems not involving rate of change, its useless.

Tell me how I synchronize a data source to RDD's concept of sample times?
Actually, what is RDD's concept of sample times? How does it determine
the start?
I would assume time starts with the first entry (or is it the time it is
created?).

If its based upon the first entry, I am actually sampling data on a very
regular (well, as regular as sleep() gets), so the stored values should
be pretty darn close to the entered values ... they are not.

On 8/19/2010 12:05 AM, Simon Hobson wrote:
> At 22:49 -0700 18/8/10, Philip Peake wrote:
>> Here is what I don't understand:
>>
>> <http://oss.oetiker.ch/rrdtool/tut/rrd-beginners.en.html>http://oss.oetiker.ch/rrdtool/tut/rrd-beginners.en.html
>> GAUGE does not save the rate of change. It saves the actual value 
>> itself. There are no divisions or calculations.
> That is correct, as far as it goes, in the context it is said. 
> However, that section is dealing with input data handling - ie 
> conversion from the numbers you put in, to numbers going to storage. 
> Other data types are converted to rates - ie (x-y)/t
>
> What happens internally is a 'black box' to me, all I know is that I 
> use gauge values a lot for logging temperature, and I get out what I 
> put in (after normalisation and consolidation).
>
> I agree it is misleading by not pointing out that the value will 
> still be normalised and consolidated just like everything else.
>
>> Looking at the source:
>>
>>             case DST_GAUGE:
>>                 old_locale = setlocale(LC_NUMERIC, "C");
>>                 errno = 0;
>>                 pdp_new[ds_idx] =
>>                     strtod(updvals[ds_idx + 1], &endptr) * interval;
>>                 if (errno) {
>>                     rrd_set_error("converting '%s' to float: %s",
>>                                   updvals[ds_idx + 1], rrd_strerror(errno));
>>                     return -1;
>>                 };
>>                 setlocale(LC_NUMERIC, old_locale);
>>                 if (endptr[0] != '\0') {
>>                     rrd_set_error
>>                         ("conversion of '%s' to float not complete: 
>> tail '%s'",
>>                          updvals[ds_idx + 1], endptr);
>>                     return -1;
>>                 }
>>                 rate = pdp_new[ds_idx] / interval;
>>                 break;
>>
>> If this line is removed, it will behave as documented.
>> I can not really see any point in this, a gauge is a gauge, its not a rate.
> No it won't - except under special circumstances that you can use 
> anyway. If you do not feed in an update **exactly** on every step 
> boundary then normalisation will occur - as per the tutorial I 
> previously posted a link to, you have read it I assume ? This is how 
> rrd works, it would require massive changes to make it work otherwise.
>