[rrd-users] Re: newbie help

[Alex van den Bogaerdt]

On Tue, Sep 23, 2003 at 01:09:08PM -0700, Sean Perry wrote:

> I am trying to graph some trouble ticket stats.  Usual stuff like number 
> of new tickets per day, closed per day, etc.  Anyone know of a good 
> example for daily queried statistics like this?

" On Tue, Sep 23, 2003 at 01:09:08PM -0700, Sean Perry wrote: "
                         ^^^^^^^^^^^^^^^^^^^

This is important.  "Per day" usually means you have to do the work
per hour, unless you happen to live in a place where time zones are
not used.

RRDtool works in UTC.  Great for doing stuff in multiple countries
but for you it means you have to take care.

You define one day to be from your midnight to the next.  This is
seven hours behind UTC; this means that you want your stuff to be
happening from 17:00 to 17:00.  This will change when daylight
saving time changes.  Luckily you can give your local time to,
for instance, perl when you are generating the time stamp for
RRDtool.

Doing the work from 17:00 UTC to 17:00 UTC, and from 16:00 UTC
to 16:00 UTC when DST is not applied, means you will have to be
able to enter data at both 16:00 and 17:00 --> largest step size
you can have is one hour.


"do the work per hour" is not as bad as it seems.  You can
update 24 rows at a time, no problem.

So, you create a database that has a resolution of one hour and
start updating each midnight (local time).  Make sure you tell
RRDtool that it is OK to get updates this far apart.  As a start:
use "--step 3600" and "DS:whatever:GAUGE:90000:0:500".

90000 is the lowest heartbeat value I can think of, it allows for
updates to be 25 hours apart: one day plus one hour because of DST.

min and max are set, in this example, to 0 and 500.

The RRA should also have rows of one hour per CDP or else you will
still end up with (normalized) values from 17:00 to 17:00 !

When you update the database, DO NOT use "rrdtool update ... N:123".
Work with explicit time stamps.

> I am also concerned about the need to specify a maximum value.  Today we 
> only have 250 tickets but who knows how many will handle next year or in 
> 3 years.

If you are sure, absolutely sure, you will never ever give wrong
input to RRDtool, you can set "U" (unlimited) as the maximum value.
By doing so you're losing the right to send mail to this list (kidding).

It is possible to change this maximum.  See "rrdtool tune".

Maybe you can trigger yourself from the front end.  Whenever it would
be sending a number that is too large, stop and cry for help.  Now you
will have to find out if you really want to enter this large number
(for values of "large" ranging from as low as 501 to maybe absurd
high numbers such as 12345678987654321).  If you need to do so, change
the setting in both the rrd and the front end.

DO NOT automate this.  It makes no sense to alter the fail safe value
from within the program that RRDtool is protecting you from.

Once you have approved the "large" amount of tickets and once you have
altered both your front end and RRDtool, send the update command.

HTH
Alex
-- 
http://www.googlism.com/index.htm?ism=alex+van+den+bogaerdt&type=1

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