[rrd-users] Re: RRDs::fetch perl methode

[Tobias Oetiker]

Yesterday steve rader wrote:

 |  > From: "Daniel J McDonald"
 |  > So, either the -r flag doesn't work, or I've misinterpreted what it does..
 |
 | "man rrdfetch" for -r reads
 |
 |  [...] will return data even if no absolute match is possible
 |
 | I think "absolute match" does not refer to the specified
 | resolution like you'd think but rather the start/end times.
 |
 | In other words, the fetch start and end have to exactly align
 | on a daily boundry.  For example, I find that (with MRTG-ish
 | RRAs) using
 |
 |  -r 86400 -s -2days -e -1day
 |
 | will fetch 86400 second resolution data
 |
 | But
 |
 |  -r 86400 -s -25hours -e -1hour
 |
 | fetches 7200 second resolution data.
 |
 |
 | Having said that, I can't explain why I find that
 |
 |  -r 86400 -s -86400 -e now
 |
 | returns 300 second interval resolution data?!

the prime focus of the fetch algorithm is to fetch
'Full Coverage' data. The RRA which keeps 1 day interval data does
not contain any data for the last hour or the last 5 minutes in
general because it only gets updated once a day. This means that
when you ask fetch to provide up to the minute data it has to
resort to the higest resolution RRA in order to find any relevant
information ...

As to the 'dayly average' question from above, I guess you want to
use a RRA with 1hour interval because this will allow you to fetch
data covering the 'local' day and not the GMT day. Obviously with 1
hour interval data you have to build the average yourself or you
have to get rrdgraph to build it for you using DEF and PRINT
arguments.

cheers
tobi

 | steve
 | - - -
 | systems & network guy
 | high energy physics
 | university of wisconsin
 |
 |
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