[rrd-users] Re: Fup: About logging the REAL value

Tobias Oetiker oetiker at ee.ethz.ch
Wed Aug 23 14:31:58 MEST 2000

Today you sent me mail regarding [rrd-users] Fup: About logging the REAL value:

*> Hi,
*> At least there is some discussion now.  This is good, no matter if a
*> change is implemented or not.
*> Now for the original problem:
*> Some room, some entry, somehow you *know* in and out going traffic can
*> only happen once every minute.  However, you do not know when this can
*> happen, it can be anywhere in this minute.

if you know that there is one update every minute you must give the
data to rrdtool every minute and also tell rrdtool for which minute
the data is ... no magic there ... works fine ... but don't expect
rrdtool to figure out which minute you mean ... 

*> A database is created.  As soon as a change is detected, the RRD is
*> updated.  The current time is used, not the available workaround.
*> 12:01:20 a person enters the room.  I know, for sure, that the amount
*> of people in the room alters from 4 to 5.  What happens in the RRD?
*> The previous interval (presumably going from 12:00 to 12:01) is updated
*> and the current value is remembered for the next update.  This update
*> happens at, for instance 12:02:20.  Another person enters the room and
*> the number of people in the room is 6.  I *know* the minimum and maximum
*> without doing any guessing, without being inaccurate.  Averaging *does*
*> introduce an error here.

yes but your precieved sampling interval seems tobe 1 second here
... so alsong as you are looking at 1 minute sampling intervals you
can not know that the MAX is 6 ... 

*> If I store the number of people this way, I strongly feel that RRDtool
*> should store the value 5 at 12:02:00.000, not 5.xx  To implement this
*> without breaking current and expected behaviour, a new DST must be
*> implemented.

mrtg will store 5 at 12:02:00.000 if you tell it to store 5 at
12:02:00.000. Very simple ... if you tell it to store 5 at
12:01:45.000 it will obviously not store 5 at 12:02:00.000 ...


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