[rrd-users] Re: adding many rows with rrdtool resize causing problems.... HELP!

Alex van den Bogaerdt alex at ergens.op.het.net
Thu Dec 26 23:20:06 MET 2002

On Thu, Dec 26, 2002 at 01:35:51PM -0700, Kempf, Reed wrote:

> The issue is that I am trying to resize about 2000 rrdtool databases because
> my requirements changed from keeping 3 months of data to keeping a years
> worth of data and I would really like to do this maintenance once instead of
> once per week.  The databases are continuously being written to and it would
> increase the possibilities of data loss if I had to do this every week not
> to mention the maintenance headache of adding rows to 2000 databases every
> week.
> If anyone can enlighten me on why the "yearly" graph will look odd if I add
> too many rows would be appreciated.

If you add rows to the 5-minute RRA these rows will contain NaN values.
If you add enough rows to satisfy a request for a complete year, you
will fetch the 5-minute rows and thus see unknown data.  You expect to
see known data thus RRDtool doesn't seem to match your expectations.

This can be circumvented:  If you ask for "--end hh:mm" "--start end-365days"
where "hh:mm" is midnight UTC represented in your local time, RRDtool
will use the original 1-day RRA and thus will not use the freshly added
5-minute rows.

In general: RRDtool will try to match your request as close as possible.

For MRTG-compatible RRDs this means RRDtool won't use the "daily" RRA
to graph a full year.  It cannot use the "weekly" or "monthly" RRAs
either so the only choice is to use the "yearly" RRA.

If you alter the amount of rows in the "daily" RRA to, for instance,
120000 rows (more than a year) RRDtool has to choose between the
"daily" RRA and the "yearly" RRA as both contain enough rows to
satisfy your request.  RRDtool will then look at the start and end
time of the data to fetch.  The "yearly" RRA contains rows that start
and end on 00:00 UTC.  The "daily" RRA contains rows that start and
end on multiples of 5 minutes.

If you request "now" it is highly likely the "daily" RRA will be
selected.  If you request n*86400 (for example: 1040947200) as the
end time and "--start end-400days" for the start time, RRDtool will
select the "yearly" RRA.

Much of what looks like rudeness in hacker circles is not intended to give
offence. Rather, it's the product of the direct, cut-through-the-bullshit
communications style that is natural to people who are more concerned about
solving problems than making others feel warm and fuzzy.


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