[rrd-users] Fetching from the beginning of an RRD file

Travis Spencer travislspencer at gmail.com
Sat Mar 3 01:12:09 CET 2007

On 2/28/07, Alex van den Bogaerdt <alex at ergens.op.het.net> wrote:

Hello Again Alex,

> Find out (using rrdtool info) how much entries there are on the wheel.
> Find out how much time is stored in each entry.  Multiply those and
> you know how much data to fetch.
> If each "step" is 300 seconds, if there are 24 steps per CDP, then each
> CDP is 7200 seconds (2 hours).  If there are 600 CDPs in this RRA, then
> there is 1200 hours (300*24*600) worth of data available.
> In this example, --start now-1200h will probably do.  Perhaps add
> --end start+24h to limit the amount of rows returned.

OK.  I'm throwing out all I know (or think I know) about SQL, putting
on my RRD hat, and trying to figure this out.  From what you said
above, I need three things to find the time of the initial entry:

1. The step value
2. The number of steps per CDP
3. The number of CDPs in the RRA

Using rrd_info, I only see the first.  Does the output of
`rra[i].rows' correspond to the number of CDPs in the RRA?  Also, I
see `rra[i].pdp_per_row'.  Is that what you mean by the number of
steps per CDP?  The output of rrd_info is showing me four RRAs with a
CF of AVERAGE; they differ by `pdp_per_row' and `cdp_prep[j].value'.
If `pdp_per_row' is what you mean by the number of steps per CDP, then
which of these RRAs do I use?

Any further clarification you can offer on this matter is much appreciated.



Travis Spencer

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