[rrd-users] Re: inserting old data into an RRD problem

[Alex van den Bogaerdt]

On Fri, Jun 18, 2004 at 01:57:44PM -0700, Allan Bailey wrote:

> I'm trying to insert (import?) old values into an RRD data file.  Here's the error I get:
> 
> $ rrdtool update test.rrd 1087473652:8.38647681652  1087473667:9.72654254627  1087473697:7.60364089061
> ERROR: illegal attempt to update using time 1087473652 when last update time is 1087542000 (minimum one second step)

This is to be expected.

If you need to alter data from the past, you need to dump the database
to xml, edit, restore.  You will be editing normalized rates, not
input values.

CPDs (rows in the RRAs) are updated from one or more PDPs.  PDPs are
built from the calculated rate.  Rates are calculated from your input.

Input values are not stored, except for the current one.  There's no
way for RRDtool to "correct" previous PDPs nor CDPs.

If you need to alter historic data, you'll have to calculate the rate
that RRDtool would have calculated.  One change in input will alter
two or more PDPs, unless each update is precisely one step and its
timestamp is precisely a whole multiple of the step size.

These two altered PDPs will change one or more CDPs in each of the
RRAs.

It is not as easy as you may think!

Alex
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